root/coders/gif.c

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DEFINITIONS

This source file includes following definitions.
  1. RelinquishLZWInfo
  2. ResetLZWInfo
  3. AcquireLZWInfo
  4. GetNextLZWCode
  5. PopLZWStack
  6. PushLZWStack
  7. ReadBlobLZWByte
  8. DecodeImage
  9. EncodeImage
  10. IsGIF
  11. ReadBlobBlock
  12. PingGIFImage
  13. ReadGIFImage
  14. RegisterGIFImage
  15. UnregisterGIFImage
  16. WriteGIFImage
/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%                             GGGG  IIIII  FFFFF                              %
%                            G        I    F                                  %
%                            G  GG    I    FFF                                %
%                            G   G    I    F                                  %
%                             GGG   IIIII  F                                  %
%                                                                             %
%                                                                             %
%            Read/Write Compuserv Graphics Interchange Format                 %
%                                                                             %
%                              Software Design                                %
%                                   Cristy                                    %
%                                 July 1992                                   %
%                                                                             %
%                                                                             %
%  Copyright 1999-2016 ImageMagick Studio LLC, a non-profit organization      %
%  dedicated to making software imaging solutions freely available.           %
%                                                                             %
%  You may not use this file except in compliance with the License.  You may  %
%  obtain a copy of the License at                                            %
%                                                                             %
%    http://www.imagemagick.org/script/license.php                            %
%                                                                             %
%  Unless required by applicable law or agreed to in writing, software        %
%  distributed under the License is distributed on an "AS IS" BASIS,          %
%  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   %
%  See the License for the specific language governing permissions and        %
%  limitations under the License.                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%
*/

/*
  Include declarations.
*/
#include "magick/studio.h"
#include "magick/attribute.h"
#include "magick/blob.h"
#include "magick/blob-private.h"
#include "magick/cache.h"
#include "magick/color.h"
#include "magick/color-private.h"
#include "magick/colormap.h"
#include "magick/colormap-private.h"
#include "magick/colorspace.h"
#include "magick/colorspace-private.h"
#include "magick/exception.h"
#include "magick/exception-private.h"
#include "magick/image.h"
#include "magick/image-private.h"
#include "magick/list.h"
#include "magick/profile.h"
#include "magick/magick.h"
#include "magick/memory_.h"
#include "magick/monitor.h"
#include "magick/monitor-private.h"
#include "magick/option.h"
#include "magick/pixel-private.h"
#include "magick/property.h"
#include "magick/quantize.h"
#include "magick/quantum-private.h"
#include "magick/static.h"
#include "magick/string_.h"
#include "magick/string-private.h"
#include "magick/module.h"

/*
  Define declarations.
*/
#define MaximumLZWBits  12
#define MaximumLZWCode  (1UL << MaximumLZWBits)

/*
  Typdef declarations.
*/
typedef struct _LZWCodeInfo
{
  unsigned char
    buffer[280];

  size_t
    count,
    bit;

  MagickBooleanType
    eof;
} LZWCodeInfo;

typedef struct _LZWStack
{
  size_t
    *codes,
    *index,
    *top;
} LZWStack;

typedef struct _LZWInfo
{
  Image
    *image;

  LZWStack
    *stack;

  MagickBooleanType
    genesis;

  size_t
    data_size,
    maximum_data_value,
    clear_code,
    end_code,
    bits,
    first_code,
    last_code,
    maximum_code,
    slot,
    *table[2];

  LZWCodeInfo
    code_info;
} LZWInfo;

/*
  Forward declarations.
*/
static inline int
  GetNextLZWCode(LZWInfo *,const size_t);

static MagickBooleanType
  WriteGIFImage(const ImageInfo *,Image *);

static ssize_t
  ReadBlobBlock(Image *,unsigned char *);

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   D e c o d e I m a g e                                                     %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  DecodeImage uncompresses an image via GIF-coding.
%
%  The format of the DecodeImage method is:
%
%      MagickBooleanType DecodeImage(Image *image,const ssize_t opacity)
%
%  A description of each parameter follows:
%
%    o image: the address of a structure of type Image.
%
%    o opacity:  The colormap index associated with the transparent color.
%
*/

static LZWInfo *RelinquishLZWInfo(LZWInfo *lzw_info)
{
  if (lzw_info->table[0] != (size_t *) NULL)
    lzw_info->table[0]=(size_t *) RelinquishMagickMemory(
      lzw_info->table[0]);
  if (lzw_info->table[1] != (size_t *) NULL)
    lzw_info->table[1]=(size_t *) RelinquishMagickMemory(
      lzw_info->table[1]);
  if (lzw_info->stack != (LZWStack *) NULL)
    {
      if (lzw_info->stack->codes != (size_t *) NULL)
        lzw_info->stack->codes=(size_t *) RelinquishMagickMemory(
          lzw_info->stack->codes);
      lzw_info->stack=(LZWStack *) RelinquishMagickMemory(lzw_info->stack);
    }
  lzw_info=(LZWInfo *) RelinquishMagickMemory(lzw_info);
  return((LZWInfo *) NULL);
}

static inline void ResetLZWInfo(LZWInfo *lzw_info)
{
  size_t
    one;

  lzw_info->bits=lzw_info->data_size+1;
  one=1;
  lzw_info->maximum_code=one << lzw_info->bits;
  lzw_info->slot=lzw_info->maximum_data_value+3;
  lzw_info->genesis=MagickTrue;
}

static LZWInfo *AcquireLZWInfo(Image *image,const size_t data_size)
{
  LZWInfo
    *lzw_info;

  register ssize_t
    i;

  size_t
    one;

  lzw_info=(LZWInfo *) AcquireMagickMemory(sizeof(*lzw_info));
  if (lzw_info == (LZWInfo *) NULL)
    return((LZWInfo *) NULL);
  (void) ResetMagickMemory(lzw_info,0,sizeof(*lzw_info));
  lzw_info->image=image;
  lzw_info->data_size=data_size;
  one=1;
  lzw_info->maximum_data_value=(one << data_size)-1;
  lzw_info->clear_code=lzw_info->maximum_data_value+1;
  lzw_info->end_code=lzw_info->maximum_data_value+2;
  lzw_info->table[0]=(size_t *) AcquireQuantumMemory(MaximumLZWCode,
    sizeof(**lzw_info->table));
  lzw_info->table[1]=(size_t *) AcquireQuantumMemory(MaximumLZWCode,
    sizeof(**lzw_info->table));
  if ((lzw_info->table[0] == (size_t *) NULL) ||
      (lzw_info->table[1] == (size_t *) NULL))
    {
      lzw_info=RelinquishLZWInfo(lzw_info);
      return((LZWInfo *) NULL);
    }
  for (i=0; i <= (ssize_t) lzw_info->maximum_data_value; i++)
  {
    lzw_info->table[0][i]=0;
    lzw_info->table[1][i]=(size_t) i;
  }
  ResetLZWInfo(lzw_info);
  lzw_info->code_info.buffer[0]='\0';
  lzw_info->code_info.buffer[1]='\0';
  lzw_info->code_info.count=2;
  lzw_info->code_info.bit=8*lzw_info->code_info.count;
  lzw_info->code_info.eof=MagickFalse;
  lzw_info->genesis=MagickTrue;
  lzw_info->stack=(LZWStack *) AcquireMagickMemory(sizeof(*lzw_info->stack));
  if (lzw_info->stack == (LZWStack *) NULL)
    {
      lzw_info=RelinquishLZWInfo(lzw_info);
      return((LZWInfo *) NULL);
    }
  lzw_info->stack->codes=(size_t *) AcquireQuantumMemory(2UL*
    MaximumLZWCode,sizeof(*lzw_info->stack->codes));
  if (lzw_info->stack->codes == (size_t *) NULL)
    {
      lzw_info=RelinquishLZWInfo(lzw_info);
      return((LZWInfo *) NULL);
    }
  lzw_info->stack->index=lzw_info->stack->codes;
  lzw_info->stack->top=lzw_info->stack->codes+2*MaximumLZWCode;
  return(lzw_info);
}

static inline int GetNextLZWCode(LZWInfo *lzw_info,const size_t bits)
{
  int
    code;

  register ssize_t
    i;

  size_t
    one;

  while (((lzw_info->code_info.bit+bits) > (8*lzw_info->code_info.count)) &&
         (lzw_info->code_info.eof == MagickFalse))
  {
    ssize_t
      count;

    lzw_info->code_info.buffer[0]=lzw_info->code_info.buffer[
      lzw_info->code_info.count-2];
    lzw_info->code_info.buffer[1]=lzw_info->code_info.buffer[
      lzw_info->code_info.count-1];
    lzw_info->code_info.bit-=8*(lzw_info->code_info.count-2);
    lzw_info->code_info.count=2;
    count=ReadBlobBlock(lzw_info->image,&lzw_info->code_info.buffer[
      lzw_info->code_info.count]);
    if (count > 0)
      lzw_info->code_info.count+=count;
    else
      lzw_info->code_info.eof=MagickTrue;
  }
  if ((lzw_info->code_info.bit+bits) > (8*lzw_info->code_info.count))
    return(-1);
  code=0;
  one=1;
  for (i=0; i < (ssize_t) bits; i++)
  {
    code|=((lzw_info->code_info.buffer[lzw_info->code_info.bit/8] &
      (one << (lzw_info->code_info.bit % 8))) != 0) << i;
    lzw_info->code_info.bit++;
  }
  return(code);
}

static inline int PopLZWStack(LZWStack *stack_info)
{
  if (stack_info->index <= stack_info->codes)
    return(-1);
  stack_info->index--;
  return((int) *stack_info->index);
}

static inline void PushLZWStack(LZWStack *stack_info,const size_t value)
{
  if (stack_info->index >= stack_info->top)
    return;
  *stack_info->index=value;
  stack_info->index++;
}

static int ReadBlobLZWByte(LZWInfo *lzw_info)
{
  int
    code;

  size_t
    one,
    value;

  ssize_t
    count;

  if (lzw_info->stack->index != lzw_info->stack->codes)
    return(PopLZWStack(lzw_info->stack));
  if (lzw_info->genesis != MagickFalse)
    {
      lzw_info->genesis=MagickFalse;
      do
      {
        lzw_info->first_code=(size_t) GetNextLZWCode(lzw_info,lzw_info->bits);
        lzw_info->last_code=lzw_info->first_code;
      } while (lzw_info->first_code == lzw_info->clear_code);
      return((int) lzw_info->first_code);
    }
  code=GetNextLZWCode(lzw_info,lzw_info->bits);
  if (code < 0)
    return(code);
  if ((size_t) code == lzw_info->clear_code)
    {
      ResetLZWInfo(lzw_info);
      return(ReadBlobLZWByte(lzw_info));
    }
  if ((size_t) code == lzw_info->end_code)
    return(-1);
  if ((size_t) code < lzw_info->slot)
    value=(size_t) code;
  else
    {
      PushLZWStack(lzw_info->stack,lzw_info->first_code);
      value=lzw_info->last_code;
    }
  count=0;
  while (value > lzw_info->maximum_data_value)
  {
    if ((size_t) count > MaximumLZWCode)
      return(-1);
    count++;
    if ((size_t) value > MaximumLZWCode)
      return(-1);
    PushLZWStack(lzw_info->stack,lzw_info->table[1][value]);
    value=lzw_info->table[0][value];
  }
  lzw_info->first_code=lzw_info->table[1][value];
  PushLZWStack(lzw_info->stack,lzw_info->first_code);
  one=1;
  if (lzw_info->slot < MaximumLZWCode)
    {
      lzw_info->table[0][lzw_info->slot]=lzw_info->last_code;
      lzw_info->table[1][lzw_info->slot]=lzw_info->first_code;
      lzw_info->slot++;
      if ((lzw_info->slot >= lzw_info->maximum_code) &&
          (lzw_info->bits < MaximumLZWBits))
        {
          lzw_info->bits++;
          lzw_info->maximum_code=one << lzw_info->bits;
        }
    }
  lzw_info->last_code=(size_t) code;
  return(PopLZWStack(lzw_info->stack));
}

static MagickBooleanType DecodeImage(Image *image,const ssize_t opacity)
{
  ExceptionInfo
    *exception;

  IndexPacket
    index;

  int
    c;

  LZWInfo
    *lzw_info;

  ssize_t
    offset,
    y;

  unsigned char
    data_size;

  size_t
    pass;

  /*
    Allocate decoder tables.
  */
  assert(image != (Image *) NULL);
  assert(image->signature == MagickSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  data_size=(unsigned char) ReadBlobByte(image);
  if (data_size > MaximumLZWBits)
    ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
  lzw_info=AcquireLZWInfo(image,data_size);
  if (lzw_info == (LZWInfo *) NULL)
    ThrowBinaryException(ResourceLimitError,"MemoryAllocationFailed",
      image->filename);
  exception=(&image->exception);
  pass=0;
  offset=0;
  for (y=0; y < (ssize_t) image->rows; y++)
  {
    register IndexPacket
      *magick_restrict indexes;

    register ssize_t
      x;

    register PixelPacket
      *magick_restrict q;

    q=QueueAuthenticPixels(image,0,offset,image->columns,1,exception);
    if (q == (PixelPacket *) NULL)
      break;
    indexes=GetAuthenticIndexQueue(image);
    for (x=0; x < (ssize_t) image->columns; )
    {
      c=ReadBlobLZWByte(lzw_info);
      if (c < 0)
        break;
      index=ConstrainColormapIndex(image,(size_t) c);
      SetPixelIndex(indexes+x,index);
      SetPixelRGBO(q,image->colormap+(ssize_t) index);
      SetPixelOpacity(q,(ssize_t) index == opacity ? TransparentOpacity :
        OpaqueOpacity);
      x++;
      q++;
    }
    if (SyncAuthenticPixels(image,exception) == MagickFalse)
      break;
    if (x < (ssize_t) image->columns)
      break;
    if (image->interlace == NoInterlace)
      offset++;
    else
      {
        switch (pass)
        {
          case 0:
          default:
          {
            offset+=8;
            break;
          }
          case 1:
          {
            offset+=8;
            break;
          }
          case 2:
          {
            offset+=4;
            break;
          }
          case 3:
          {
            offset+=2;
            break;
          }
        }
      if ((pass == 0) && (offset >= (ssize_t) image->rows))
        {
          pass++;
          offset=4;
        }
      if ((pass == 1) && (offset >= (ssize_t) image->rows))
        {
          pass++;
          offset=2;
        }
      if ((pass == 2) && (offset >= (ssize_t) image->rows))
        {
          pass++;
          offset=1;
        }
    }
  }
  lzw_info=RelinquishLZWInfo(lzw_info);
  if (y < (ssize_t) image->rows)
    ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
  return(MagickTrue);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   E n c o d e I m a g e                                                     %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  EncodeImage compresses an image via GIF-coding.
%
%  The format of the EncodeImage method is:
%
%      MagickBooleanType EncodeImage(const ImageInfo *image_info,Image *image,
%        const size_t data_size)
%
%  A description of each parameter follows:
%
%    o image_info: the image info.
%
%    o image: the address of a structure of type Image.
%
%    o data_size:  The number of bits in the compressed packet.
%
*/
static MagickBooleanType EncodeImage(const ImageInfo *image_info,Image *image,
  const size_t data_size)
{
#define MaxCode(number_bits)  ((one << (number_bits))-1)
#define MaxHashTable  5003
#define MaxGIFBits  12UL
#define MaxGIFTable  (1UL << MaxGIFBits)
#define GIFOutputCode(code) \
{ \
  /*  \
    Emit a code. \
  */ \
  if (bits > 0) \
    datum|=(code) << bits; \
  else \
    datum=code; \
  bits+=number_bits; \
  while (bits >= 8) \
  { \
    /*  \
      Add a character to current packet. \
    */ \
    packet[length++]=(unsigned char) (datum & 0xff); \
    if (length >= 254) \
      { \
        (void) WriteBlobByte(image,(unsigned char) length); \
        (void) WriteBlob(image,length,packet); \
        length=0; \
      } \
    datum>>=8; \
    bits-=8; \
  } \
  if (free_code > max_code)  \
    { \
      number_bits++; \
      if (number_bits == MaxGIFBits) \
        max_code=MaxGIFTable; \
      else \
        max_code=MaxCode(number_bits); \
    } \
}

  IndexPacket
    index;

  short
    *hash_code,
    *hash_prefix,
    waiting_code;

  size_t
    bits,
    clear_code,
    datum,
    end_of_information_code,
    free_code,
    length,
    max_code,
    next_pixel,
    number_bits,
    one,
    pass;

  ssize_t
    displacement,
    offset,
    k,
    y;

  unsigned char
    *packet,
    *hash_suffix;

  /*
    Allocate encoder tables.
  */
  assert(image != (Image *) NULL);
  one=1;
  packet=(unsigned char *) AcquireQuantumMemory(256,sizeof(*packet));
  hash_code=(short *) AcquireQuantumMemory(MaxHashTable,sizeof(*hash_code));
  hash_prefix=(short *) AcquireQuantumMemory(MaxHashTable,sizeof(*hash_prefix));
  hash_suffix=(unsigned char *) AcquireQuantumMemory(MaxHashTable,
    sizeof(*hash_suffix));
  if ((packet == (unsigned char *) NULL) || (hash_code == (short *) NULL) ||
      (hash_prefix == (short *) NULL) ||
      (hash_suffix == (unsigned char *) NULL))
    {
      if (packet != (unsigned char *) NULL)
        packet=(unsigned char *) RelinquishMagickMemory(packet);
      if (hash_code != (short *) NULL)
        hash_code=(short *) RelinquishMagickMemory(hash_code);
      if (hash_prefix != (short *) NULL)
        hash_prefix=(short *) RelinquishMagickMemory(hash_prefix);
      if (hash_suffix != (unsigned char *) NULL)
        hash_suffix=(unsigned char *) RelinquishMagickMemory(hash_suffix);
      return(MagickFalse);
    }
  /*
    Initialize GIF encoder.
  */
  (void) ResetMagickMemory(hash_code,0,MaxHashTable*sizeof(*hash_code));
  (void) ResetMagickMemory(hash_prefix,0,MaxHashTable*sizeof(*hash_prefix));
  (void) ResetMagickMemory(hash_suffix,0,MaxHashTable*sizeof(*hash_suffix));
  number_bits=data_size;
  max_code=MaxCode(number_bits);
  clear_code=((short) one << (data_size-1));
  end_of_information_code=clear_code+1;
  free_code=clear_code+2;
  length=0;
  datum=0;
  bits=0;
  GIFOutputCode(clear_code);
  /*
    Encode pixels.
  */
  offset=0;
  pass=0;
  waiting_code=0;
  for (y=0; y < (ssize_t) image->rows; y++)
  {
    register const IndexPacket
      *magick_restrict indexes;

    register const PixelPacket
      *magick_restrict p;

    register ssize_t
      x;

    p=GetVirtualPixels(image,0,offset,image->columns,1,&image->exception);
    if (p == (const PixelPacket *) NULL)
      break;
    indexes=GetVirtualIndexQueue(image);
    if (y == 0)
      waiting_code=(short) (*indexes);
    for (x=(ssize_t) (y == 0 ? 1 : 0); x < (ssize_t) image->columns; x++)
    {
      /*
        Probe hash table.
      */
      index=(IndexPacket) ((size_t) GetPixelIndex(indexes+x) & 0xff);
      p++;
      k=(ssize_t) (((size_t) index << (MaxGIFBits-8))+waiting_code);
      if (k >= MaxHashTable)
        k-=MaxHashTable;
      next_pixel=MagickFalse;
      displacement=1;
      if (hash_code[k] > 0)
        {
          if ((hash_prefix[k] == waiting_code) &&
              (hash_suffix[k] == (unsigned char) index))
            {
              waiting_code=hash_code[k];
              continue;
            }
          if (k != 0)
            displacement=MaxHashTable-k;
          for ( ; ; )
          {
            k-=displacement;
            if (k < 0)
              k+=MaxHashTable;
            if (hash_code[k] == 0)
              break;
            if ((hash_prefix[k] == waiting_code) &&
                (hash_suffix[k] == (unsigned char) index))
              {
                waiting_code=hash_code[k];
                next_pixel=MagickTrue;
                break;
              }
          }
          if (next_pixel != MagickFalse)
            continue;
        }
      GIFOutputCode((size_t) waiting_code);
      if (free_code < MaxGIFTable)
        {
          hash_code[k]=(short) free_code++;
          hash_prefix[k]=waiting_code;
          hash_suffix[k]=(unsigned char) index;
        }
      else
        {
          /*
            Fill the hash table with empty entries.
          */
          for (k=0; k < MaxHashTable; k++)
            hash_code[k]=0;
          /*
            Reset compressor and issue a clear code.
          */
          free_code=clear_code+2;
          GIFOutputCode(clear_code);
          number_bits=data_size;
          max_code=MaxCode(number_bits);
        }
      waiting_code=(short) index;
    }
    if (image_info->interlace == NoInterlace)
      offset++;
    else
      switch (pass)
      {
        case 0:
        default:
        {
          offset+=8;
          if (offset >= (ssize_t) image->rows)
            {
              pass++;
              offset=4;
            }
          break;
        }
        case 1:
        {
          offset+=8;
          if (offset >= (ssize_t) image->rows)
            {
              pass++;
              offset=2;
            }
          break;
        }
        case 2:
        {
          offset+=4;
          if (offset >= (ssize_t) image->rows)
            {
              pass++;
              offset=1;
            }
          break;
        }
        case 3:
        {
          offset+=2;
          break;
        }
      }
  }
  /*
    Flush out the buffered code.
  */
  GIFOutputCode((size_t) waiting_code);
  GIFOutputCode(end_of_information_code);
  if (bits > 0)
    {
      /*
        Add a character to current packet.
      */
      packet[length++]=(unsigned char) (datum & 0xff);
      if (length >= 254)
        {
          (void) WriteBlobByte(image,(unsigned char) length);
          (void) WriteBlob(image,length,packet);
          length=0;
        }
    }
  /*
    Flush accumulated data.
  */
  if (length > 0)
    {
      (void) WriteBlobByte(image,(unsigned char) length);
      (void) WriteBlob(image,length,packet);
    }
  /*
    Free encoder memory.
  */
  hash_suffix=(unsigned char *) RelinquishMagickMemory(hash_suffix);
  hash_prefix=(short *) RelinquishMagickMemory(hash_prefix);
  hash_code=(short *) RelinquishMagickMemory(hash_code);
  packet=(unsigned char *) RelinquishMagickMemory(packet);
  return(MagickTrue);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   I s G I F                                                                 %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  IsGIF() returns MagickTrue if the image format type, identified by the
%  magick string, is GIF.
%
%  The format of the IsGIF method is:
%
%      MagickBooleanType IsGIF(const unsigned char *magick,const size_t length)
%
%  A description of each parameter follows:
%
%    o magick: compare image format pattern against these bytes.
%
%    o length: Specifies the length of the magick string.
%
*/
static MagickBooleanType IsGIF(const unsigned char *magick,const size_t length)
{
  if (length < 4)
    return(MagickFalse);
  if (LocaleNCompare((char *) magick,"GIF8",4) == 0)
    return(MagickTrue);
  return(MagickFalse);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+  R e a d B l o b B l o c k                                                  %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  ReadBlobBlock() reads data from the image file and returns it.  The
%  amount of data is determined by first reading a count byte.  The number
%  of bytes read is returned.
%
%  The format of the ReadBlobBlock method is:
%
%      size_t ReadBlobBlock(Image *image,unsigned char *data)
%
%  A description of each parameter follows:
%
%    o image: the image.
%
%    o data:  Specifies an area to place the information requested from
%      the file.
%
*/
static ssize_t ReadBlobBlock(Image *image,unsigned char *data)
{
  ssize_t
    count;

  unsigned char
    block_count;

  assert(image != (Image *) NULL);
  assert(image->signature == MagickSignature);
  assert(data != (unsigned char *) NULL);
  count=ReadBlob(image,1,&block_count);
  if (count != 1)
    return(0);
  count=ReadBlob(image,(size_t) block_count,data);
  if (count != (ssize_t) block_count)
    return(0);
  return(count);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   R e a d G I F I m a g e                                                   %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  ReadGIFImage() reads a Compuserve Graphics image file and returns it.
%  It allocates the memory necessary for the new Image structure and returns a
%  pointer to the new image.
%
%  The format of the ReadGIFImage method is:
%
%      Image *ReadGIFImage(const ImageInfo *image_info,ExceptionInfo *exception)
%
%  A description of each parameter follows:
%
%    o image_info: the image info.
%
%    o exception: return any errors or warnings in this structure.
%
*/
static MagickBooleanType PingGIFImage(Image *image)
{
  unsigned char
    buffer[256],
    length,
    data_size;

  assert(image != (Image *) NULL);
  assert(image->signature == MagickSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  if (ReadBlob(image,1,&data_size) != 1)
    ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
  if (data_size > MaximumLZWBits)
    ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
  if (ReadBlob(image,1,&length) != 1)
    ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
  while (length != 0)
  {
    if (ReadBlob(image,length,buffer) != (ssize_t) length)
      ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
    if (ReadBlob(image,1,&length) != 1)
      ThrowBinaryException(CorruptImageError,"CorruptImage",image->filename);
  }
  return(MagickTrue);
}

static Image *ReadGIFImage(const ImageInfo *image_info,ExceptionInfo *exception)
{
#define BitSet(byte,bit)  (((byte) & (bit)) == (bit))
#define LSBFirstOrder(x,y)  (((y) << 8) | (x))

  Image
    *image,
    *meta_image;

  int
    number_extensionss=0;

  MagickBooleanType
    status;

  RectangleInfo
    page;

  register ssize_t
    i;

  register unsigned char
    *p;

  size_t
    delay,
    dispose,
    duration,
    global_colors,
    image_count,
    iterations,
    one;

  ssize_t
    count,
    opacity;

  unsigned char
    background,
    c,
    flag,
    *global_colormap,
    header[MaxTextExtent],
    magick[12];

  /*
    Open image file.
  */
  assert(image_info != (const ImageInfo *) NULL);
  assert(image_info->signature == MagickSignature);
  if (image_info->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",
      image_info->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickSignature);
  image=AcquireImage(image_info);
  status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
  if (status == MagickFalse)
    {
      image=DestroyImageList(image);
      return((Image *) NULL);
    }
  /*
    Determine if this a GIF file.
  */
  count=ReadBlob(image,6,magick);
  if ((count != 6) || ((LocaleNCompare((char *) magick,"GIF87",5) != 0) &&
      (LocaleNCompare((char *) magick,"GIF89",5) != 0)))
    ThrowReaderException(CorruptImageError,"ImproperImageHeader");
  page.width=ReadBlobLSBShort(image);
  page.height=ReadBlobLSBShort(image);
  flag=(unsigned char) ReadBlobByte(image);
  background=(unsigned char) ReadBlobByte(image);
  c=(unsigned char) ReadBlobByte(image);  /* reserved */
  one=1;
  global_colors=one << (((size_t) flag & 0x07)+1);
  global_colormap=(unsigned char *) AcquireQuantumMemory((size_t)
    MagickMax(global_colors,256),3UL*sizeof(*global_colormap));
  if (global_colormap == (unsigned char *) NULL)
    ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
  if (BitSet((int) flag,0x80) != 0)
    {
      count=ReadBlob(image,(size_t) (3*global_colors),global_colormap);
      if (count != (ssize_t) (3*global_colors))
        {
          global_colormap=(unsigned char *) RelinquishMagickMemory(
            global_colormap);
          ThrowReaderException(CorruptImageError,"InsufficientImageDataInFile");
        }
    }
  delay=0;
  dispose=0;
  duration=0;
  iterations=1;
  opacity=(-1);
  image_count=0;
  meta_image=AcquireImage(image_info);  /* metadata container */
  for ( ; ; )
  {
    count=ReadBlob(image,1,&c);
    if (count != 1)
      break;
    if (c == (unsigned char) ';')
      break;  /* terminator */
    if (c == (unsigned char) '!')
      {
        /*
          GIF Extension block.
        */

        count=ReadBlob(image,1,&c);
        if (count != 1)
          {
            global_colormap=(unsigned char *) RelinquishMagickMemory(
              global_colormap);
            ThrowReaderException(CorruptImageError,
              "UnableToReadExtensionBlock");
          }
        switch (c)
        {
          case 0xf9:
          {
            /*
              Read graphics control extension.
            */
            while (ReadBlobBlock(image,header) != 0) ;
            dispose=(size_t) (header[0] >> 2);
            delay=(size_t) ((header[2] << 8) | header[1]);
            if ((ssize_t) (header[0] & 0x01) == 0x01)
              opacity=(ssize_t) header[3];
            break;
          }
          case 0xfe:
          {
            char
              *comments;

            size_t
              length;

            /*
              Read comment extension.
            */
            comments=AcquireString((char *) NULL);
            for (length=0; ; length+=count)
            {
              count=(ssize_t) ReadBlobBlock(image,header);
              if (count == 0)
                break;
              header[count]='\0';
              (void) ConcatenateString(&comments,(const char *) header);
            }
            (void) SetImageProperty(meta_image,"comment",comments);
            comments=DestroyString(comments);
            break;
          }
          case 0xff:
          {
            MagickBooleanType
              loop;

            /*
              Read Netscape Loop extension.
            */
            loop=MagickFalse;
            if (ReadBlobBlock(image,header) != 0)
              loop=LocaleNCompare((char *) header,"NETSCAPE2.0",11) == 0 ?
                MagickTrue : MagickFalse;
            if (loop != MagickFalse)
              {
                while (ReadBlobBlock(image,header) != 0)
                  iterations=(size_t) ((header[2] << 8) | header[1]);
                break;
              }
            else
              {
                char
                  name[MaxTextExtent];

                int
                  block_length,
                  info_length,
                  reserved_length;

                MagickBooleanType
                  i8bim,
                  icc,
                  iptc,
                  magick;

                StringInfo
                  *profile;

                unsigned char
                  *info;

                /*
                  Store GIF application extension as a generic profile.
                */
                icc=LocaleNCompare((char *) header,"ICCRGBG1012",11) == 0 ?
                  MagickTrue : MagickFalse;
                magick=LocaleNCompare((char *) header,"ImageMagick",11) == 0 ?
                  MagickTrue : MagickFalse;
                i8bim=LocaleNCompare((char *) header,"MGK8BIM0000",11) == 0 ?
                  MagickTrue : MagickFalse;
                iptc=LocaleNCompare((char *) header,"MGKIPTC0000",11) == 0 ?
                  MagickTrue : MagickFalse;
                number_extensionss++;
                (void) LogMagickEvent(CoderEvent,GetMagickModule(),
                  "    Reading GIF application extension");
                info=(unsigned char *) AcquireQuantumMemory(255UL,
                  sizeof(*info));
                if (info == (unsigned char *) NULL)
                  ThrowReaderException(ResourceLimitError,
                    "MemoryAllocationFailed");
                reserved_length=255;
                for (info_length=0; ; )
                {
                  block_length=(int) ReadBlobBlock(image,&info[info_length]);
                  if (block_length == 0)
                    break;
                  info_length+=block_length;
                  if (info_length > (reserved_length-255))
                    {
                      reserved_length+=4096;
                      info=(unsigned char *) ResizeQuantumMemory(info,(size_t)
                        reserved_length,sizeof(*info));
                      if (info == (unsigned char *) NULL)
                        ThrowReaderException(ResourceLimitError,
                          "MemoryAllocationFailed");
                    }
                }
                profile=BlobToStringInfo(info,(size_t) info_length);
                if (profile == (StringInfo *) NULL)
                  ThrowReaderException(ResourceLimitError,
                    "MemoryAllocationFailed");
                if (i8bim != MagickFalse)
                  (void) CopyMagickString(name,"8bim",sizeof(name));
                else if (icc != MagickFalse)
                  (void) CopyMagickString(name,"icc",sizeof(name));
                else if (iptc != MagickFalse)
                  (void) CopyMagickString(name,"iptc",sizeof(name));
                else if (magick != MagickFalse)
                  {
                    (void) CopyMagickString(name,"magick",sizeof(name));
                    meta_image->gamma=StringToDouble((char *) info+6,
                      (char **) NULL);
                  }
                else
                  (void) FormatLocaleString(name,sizeof(name),"gif:%.11s",
                    header);
                info=(unsigned char *) RelinquishMagickMemory(info);
                if (magick == MagickFalse)
                  (void) SetImageProfile(meta_image,name,profile);
                profile=DestroyStringInfo(profile);
                (void) LogMagickEvent(CoderEvent,GetMagickModule(),
                  "      profile name=%s",name);
              }
            break;
          }
          default:
          {
            while (ReadBlobBlock(image,header) != 0) ;
            break;
          }
        }
      }
    if (c != (unsigned char) ',')
      continue;
    if (image_count != 0)
      {
        /*
          Allocate next image structure.
        */
        AcquireNextImage(image_info,image);
        if (GetNextImageInList(image) == (Image *) NULL)
          {
            image=DestroyImageList(image);
            global_colormap=(unsigned char *) RelinquishMagickMemory(
              global_colormap);
            return((Image *) NULL);
          }
        image=SyncNextImageInList(image);
      }
    image_count++;
    /*
      Read image attributes.
    */
    meta_image->scene=image->scene;
    (void) CloneImageProperties(image,meta_image);
    DestroyImageProperties(meta_image);
    (void) CloneImageProfiles(image,meta_image);
    DestroyImageProfiles(meta_image);
    image->storage_class=PseudoClass;
    image->compression=LZWCompression;
    page.x=(ssize_t) ReadBlobLSBShort(image);
    page.y=(ssize_t) ReadBlobLSBShort(image);
    image->columns=ReadBlobLSBShort(image);
    image->rows=ReadBlobLSBShort(image);
    image->depth=8;
    flag=(unsigned char) ReadBlobByte(image);
    image->interlace=BitSet((int) flag,0x40) != 0 ? GIFInterlace : NoInterlace;
    image->colors=BitSet((int) flag,0x80) == 0 ? global_colors : one <<
      ((size_t) (flag & 0x07)+1);
    if (opacity >= (ssize_t) image->colors)
      opacity=(-1);
    image->page.width=page.width;
    image->page.height=page.height;
    image->page.y=page.y;
    image->page.x=page.x;
    image->delay=delay;
    image->iterations=iterations;
    image->ticks_per_second=100;
    image->dispose=(DisposeType) dispose;
    image->matte=opacity >= 0 ? MagickTrue : MagickFalse;
    delay=0;
    dispose=0;
    if ((image->columns == 0) || (image->rows == 0))
      {
        global_colormap=(unsigned char *) RelinquishMagickMemory(
          global_colormap);
        ThrowReaderException(CorruptImageError,"NegativeOrZeroImageSize");
      }
    /*
      Inititialize colormap.
    */
    if (AcquireImageColormap(image,image->colors) == MagickFalse)
      {
        global_colormap=(unsigned char *) RelinquishMagickMemory(
          global_colormap);
        ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
      }
    if (BitSet((int) flag,0x80) == 0)
      {
        /*
          Use global colormap.
        */
        p=global_colormap;
        for (i=0; i < (ssize_t) image->colors; i++)
        {
          image->colormap[i].red=ScaleCharToQuantum(*p++);
          image->colormap[i].green=ScaleCharToQuantum(*p++);
          image->colormap[i].blue=ScaleCharToQuantum(*p++);
          if (i == opacity)
            {
              image->colormap[i].opacity=(Quantum) TransparentOpacity;
              image->transparent_color=image->colormap[opacity];
            }
        }
        image->background_color=image->colormap[MagickMin((ssize_t) background,
          (ssize_t) image->colors-1)];
      }
    else
      {
        unsigned char
          *colormap;

        /*
          Read local colormap.
        */
        colormap=(unsigned char *) AcquireQuantumMemory(image->colors,3*
          sizeof(*colormap));
        if (colormap == (unsigned char *) NULL)
          {
            global_colormap=(unsigned char *) RelinquishMagickMemory(
              global_colormap);
            ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
          }
        count=ReadBlob(image,(3*image->colors)*sizeof(*colormap),colormap);
        if (count != (ssize_t) (3*image->colors))
          {
            global_colormap=(unsigned char *) RelinquishMagickMemory(
              global_colormap);
            colormap=(unsigned char *) RelinquishMagickMemory(colormap);
            ThrowReaderException(CorruptImageError,
              "InsufficientImageDataInFile");
          }
        p=colormap;
        for (i=0; i < (ssize_t) image->colors; i++)
        {
          image->colormap[i].red=ScaleCharToQuantum(*p++);
          image->colormap[i].green=ScaleCharToQuantum(*p++);
          image->colormap[i].blue=ScaleCharToQuantum(*p++);
          if (i == opacity)
            image->colormap[i].opacity=(Quantum) TransparentOpacity;
        }
        colormap=(unsigned char *) RelinquishMagickMemory(colormap);
      }
    if (image->gamma == 1.0)
      {
        for (i=0; i < (ssize_t) image->colors; i++)
          if (IsGrayPixel(image->colormap+i) == MagickFalse)
            break;
        (void) SetImageColorspace(image,i == (ssize_t) image->colors ?
          GRAYColorspace : RGBColorspace);
      }
    if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0))
      if (image->scene >= (image_info->scene+image_info->number_scenes-1))
        break;
    status=SetImageExtent(image,image->columns,image->rows);
    if (status == MagickFalse)
      {
        InheritException(exception,&image->exception);
        return(DestroyImageList(image));
      }
    /*
      Decode image.
    */
    if (image_info->ping != MagickFalse)
      status=PingGIFImage(image);
    else
      status=DecodeImage(image,opacity);
    if ((image_info->ping == MagickFalse) && (status == MagickFalse))
      {
        global_colormap=(unsigned char *) RelinquishMagickMemory(
          global_colormap);
        ThrowReaderException(CorruptImageError,"CorruptImage");
      }
    duration+=image->delay*image->iterations;
    if (image_info->number_scenes != 0)
      if (image->scene >= (image_info->scene+image_info->number_scenes-1))
        break;
    opacity=(-1);
    status=SetImageProgress(image,LoadImageTag,(MagickOffsetType) image->scene-
      1,image->scene);
    if (status == MagickFalse)
      break;
  }
  image->duration=duration;
  meta_image=DestroyImage(meta_image);
  global_colormap=(unsigned char *) RelinquishMagickMemory(global_colormap);
  if ((image->columns == 0) || (image->rows == 0))
    ThrowReaderException(CorruptImageError,"NegativeOrZeroImageSize");
  (void) CloseBlob(image);
  return(GetFirstImageInList(image));
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   R e g i s t e r G I F I m a g e                                           %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  RegisterGIFImage() adds properties for the GIF image format to
%  the list of supported formats.  The properties include the image format
%  tag, a method to read and/or write the format, whether the format
%  supports the saving of more than one frame to the same file or blob,
%  whether the format supports native in-memory I/O, and a brief
%  description of the format.
%
%  The format of the RegisterGIFImage method is:
%
%      size_t RegisterGIFImage(void)
%
*/
ModuleExport size_t RegisterGIFImage(void)
{
  MagickInfo
    *entry;

  entry=SetMagickInfo("GIF");
  entry->decoder=(DecodeImageHandler *) ReadGIFImage;
  entry->encoder=(EncodeImageHandler *) WriteGIFImage;
  entry->magick=(IsImageFormatHandler *) IsGIF;
  entry->description=ConstantString("CompuServe graphics interchange format");
  entry->mime_type=ConstantString("image/gif");
  entry->module=ConstantString("GIF");
  (void) RegisterMagickInfo(entry);
  entry=SetMagickInfo("GIF87");
  entry->decoder=(DecodeImageHandler *) ReadGIFImage;
  entry->encoder=(EncodeImageHandler *) WriteGIFImage;
  entry->magick=(IsImageFormatHandler *) IsGIF;
  entry->adjoin=MagickFalse;
  entry->description=ConstantString("CompuServe graphics interchange format");
  entry->version=ConstantString("version 87a");
  entry->mime_type=ConstantString("image/gif");
  entry->module=ConstantString("GIF");
  (void) RegisterMagickInfo(entry);
  return(MagickImageCoderSignature);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   U n r e g i s t e r G I F I m a g e                                       %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  UnregisterGIFImage() removes format registrations made by the
%  GIF module from the list of supported formats.
%
%  The format of the UnregisterGIFImage method is:
%
%      UnregisterGIFImage(void)
%
*/
ModuleExport void UnregisterGIFImage(void)
{
  (void) UnregisterMagickInfo("GIF");
  (void) UnregisterMagickInfo("GIF87");
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
%   W r i t e G I F I m a g e                                                 %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  WriteGIFImage() writes an image to a file in the Compuserve Graphics
%  image format.
%
%  The format of the WriteGIFImage method is:
%
%      MagickBooleanType WriteGIFImage(const ImageInfo *image_info,
%        Image *image)
%
%  A description of each parameter follows.
%
%    o image_info: the image info.
%
%    o image:  The image.
%
*/
static MagickBooleanType WriteGIFImage(const ImageInfo *image_info,Image *image)
{
  int
    c;

  ImageInfo
    *write_info;

  InterlaceType
    interlace;

  MagickBooleanType
    status;

  MagickOffsetType
    scene;

  RectangleInfo
    page;

  register ssize_t
    i;

  register unsigned char
    *q;

  size_t
    bits_per_pixel,
    delay,
    length,
    one;

  ssize_t
    j,
    opacity;

  unsigned char
    *colormap,
    *global_colormap;

  /*
    Open output image file.
  */
  assert(image_info != (const ImageInfo *) NULL);
  assert(image_info->signature == MagickSignature);
  assert(image != (Image *) NULL);
  assert(image->signature == MagickSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  status=OpenBlob(image_info,image,WriteBinaryBlobMode,&image->exception);
  if (status == MagickFalse)
    return(status);
  /*
    Allocate colormap.
  */
  global_colormap=(unsigned char *) AcquireQuantumMemory(768UL,
    sizeof(*global_colormap));
  colormap=(unsigned char *) AcquireQuantumMemory(768UL,sizeof(*colormap));
  if ((global_colormap == (unsigned char *) NULL) ||
      (colormap == (unsigned char *) NULL))
    ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
  for (i=0; i < 768; i++)
    colormap[i]=(unsigned char) 0;
  /*
    Write GIF header.
  */
  write_info=CloneImageInfo(image_info);
  if (LocaleCompare(write_info->magick,"GIF87") != 0)
    (void) WriteBlob(image,6,(unsigned char *) "GIF89a");
  else
    {
      (void) WriteBlob(image,6,(unsigned char *) "GIF87a");
      write_info->adjoin=MagickFalse;
    }
  /*
    Determine image bounding box.
  */
  page.width=image->columns;
  if (image->page.width > page.width)
    page.width=image->page.width;
  page.height=image->rows;
  if (image->page.height > page.height)
    page.height=image->page.height;
  page.x=image->page.x;
  page.y=image->page.y;
  (void) WriteBlobLSBShort(image,(unsigned short) page.width);
  (void) WriteBlobLSBShort(image,(unsigned short) page.height);
  /*
    Write images to file.
  */
  interlace=write_info->interlace;
  if ((write_info->adjoin != MagickFalse) &&
      (GetNextImageInList(image) != (Image *) NULL))
    interlace=NoInterlace;
  scene=0;
  one=1;
  do
  {
    (void) TransformImageColorspace(image,sRGBColorspace);
    opacity=(-1);
    if (IsOpaqueImage(image,&image->exception) != MagickFalse)
      {
        if ((image->storage_class == DirectClass) || (image->colors > 256))
          (void) SetImageType(image,PaletteType);
      }
    else
      {
        double
          alpha,
          beta;

        /*
          Identify transparent colormap index.
        */
        if ((image->storage_class == DirectClass) || (image->colors > 256))
          (void) SetImageType(image,PaletteBilevelMatteType);
        for (i=0; i < (ssize_t) image->colors; i++)
          if (image->colormap[i].opacity != OpaqueOpacity)
            {
              if (opacity < 0)
                {
                  opacity=i;
                  continue;
                }
              alpha=fabs((double) image->colormap[i].opacity-
                TransparentOpacity);
              beta=fabs((double) image->colormap[opacity].opacity-
                TransparentOpacity);
              if (alpha < beta)
                opacity=i;
            }
        if (opacity == -1)
          {
            (void) SetImageType(image,PaletteBilevelMatteType);
            for (i=0; i < (ssize_t) image->colors; i++)
              if (image->colormap[i].opacity != OpaqueOpacity)
                {
                  if (opacity < 0)
                    {
                      opacity=i;
                      continue;
                    }
                  alpha=fabs((double) image->colormap[i].opacity-
                    TransparentOpacity);
                  beta=fabs((double) image->colormap[opacity].opacity-
                    TransparentOpacity);
                  if (alpha < beta)
                    opacity=i;
                }
          }
        if (opacity >= 0)
          {
            image->colormap[opacity].red=image->transparent_color.red;
            image->colormap[opacity].green=image->transparent_color.green;
            image->colormap[opacity].blue=image->transparent_color.blue;
          }
      }
    if ((image->storage_class == DirectClass) || (image->colors > 256))
      ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
    for (bits_per_pixel=1; bits_per_pixel < 8; bits_per_pixel++)
      if ((one << bits_per_pixel) >= image->colors)
        break;
    q=colormap;
    for (i=0; i < (ssize_t) image->colors; i++)
    {
      *q++=ScaleQuantumToChar(image->colormap[i].red);
      *q++=ScaleQuantumToChar(image->colormap[i].green);
      *q++=ScaleQuantumToChar(image->colormap[i].blue);
    }
    for ( ; i < (ssize_t) (one << bits_per_pixel); i++)
    {
      *q++=(unsigned char) 0x0;
      *q++=(unsigned char) 0x0;
      *q++=(unsigned char) 0x0;
    }
    if ((GetPreviousImageInList(image) == (Image *) NULL) ||
        (write_info->adjoin == MagickFalse))
      {
        /*
          Write global colormap.
        */
        c=0x80;
        c|=(8-1) << 4;  /* color resolution */
        c|=(bits_per_pixel-1);   /* size of global colormap */
        (void) WriteBlobByte(image,(unsigned char) c);
        for (j=0; j < (ssize_t) image->colors; j++)
          if (IsColorEqual(&image->background_color,image->colormap+j))
            break;
        (void) WriteBlobByte(image,(unsigned char)
          (j == (ssize_t) image->colors ? 0 : j));  /* background color */
        (void) WriteBlobByte(image,(unsigned char) 0x00);  /* reserved */
        length=(size_t) (3*(one << bits_per_pixel));
        (void) WriteBlob(image,length,colormap);
        for (j=0; j < 768; j++)
          global_colormap[j]=colormap[j];
      }
    if (LocaleCompare(write_info->magick,"GIF87") != 0)
      {
        const char
          *value;

        /*
          Write graphics control extension.
        */
        (void) WriteBlobByte(image,(unsigned char) 0x21);
        (void) WriteBlobByte(image,(unsigned char) 0xf9);
        (void) WriteBlobByte(image,(unsigned char) 0x04);
        c=image->dispose << 2;
        if (opacity >= 0)
          c|=0x01;
        (void) WriteBlobByte(image,(unsigned char) c);
        delay=(size_t) (100*image->delay/MagickMax((size_t)
          image->ticks_per_second,1));
        (void) WriteBlobLSBShort(image,(unsigned short) delay);
        (void) WriteBlobByte(image,(unsigned char) (opacity >= 0 ? opacity :
          0));
        (void) WriteBlobByte(image,(unsigned char) 0x00);
        value=GetImageProperty(image,"comment");
        if ((LocaleCompare(write_info->magick,"GIF87") != 0) &&
            (value != (const char *) NULL))
          {
            register const char
              *p;

            size_t
              count;

            /*
              Write comment extension.
            */
            (void) WriteBlobByte(image,(unsigned char) 0x21);
            (void) WriteBlobByte(image,(unsigned char) 0xfe);
            for (p=value; *p != '\0'; )
            {
              count=MagickMin(strlen(p),255);
              (void) WriteBlobByte(image,(unsigned char) count);
              for (i=0; i < (ssize_t) count; i++)
                (void) WriteBlobByte(image,(unsigned char) *p++);
            }
            (void) WriteBlobByte(image,(unsigned char) 0x00);
          }
        if ((GetPreviousImageInList(image) == (Image *) NULL) &&
            (GetNextImageInList(image) != (Image *) NULL) &&
            (image->iterations != 1))
          {
            /*
              Write Netscape Loop extension.
            */
            (void) LogMagickEvent(CoderEvent,GetMagickModule(),
               "  Writing GIF Extension %s","NETSCAPE2.0");
            (void) WriteBlobByte(image,(unsigned char) 0x21);
            (void) WriteBlobByte(image,(unsigned char) 0xff);
            (void) WriteBlobByte(image,(unsigned char) 0x0b);
            (void) WriteBlob(image,11,(unsigned char *) "NETSCAPE2.0");
            (void) WriteBlobByte(image,(unsigned char) 0x03);
            (void) WriteBlobByte(image,(unsigned char) 0x01);
            (void) WriteBlobLSBShort(image,(unsigned short) image->iterations);
            (void) WriteBlobByte(image,(unsigned char) 0x00);
          }
        if ((image->gamma != 1.0f/2.2f))
          {
            char
              attributes[MaxTextExtent];

            ssize_t
              count;

            /*
              Write ImageMagick extension.
            */
            (void) LogMagickEvent(CoderEvent,GetMagickModule(),
               "  Writing GIF Extension %s","ImageMagick");
            (void) WriteBlobByte(image,(unsigned char) 0x21);
            (void) WriteBlobByte(image,(unsigned char) 0xff);
            (void) WriteBlobByte(image,(unsigned char) 0x0b);
            (void) WriteBlob(image,11,(unsigned char *) "ImageMagick");
            count=FormatLocaleString(attributes,MaxTextExtent,"gamma=%g",
              image->gamma);
            (void) WriteBlobByte(image,(unsigned char) count);
            (void) WriteBlob(image,(size_t) count,(unsigned char *) attributes);
            (void) WriteBlobByte(image,(unsigned char) 0x00);
          }
        ResetImageProfileIterator(image);
        for ( ; ; )
        {
          char
            *name;

          const StringInfo
            *profile;

          name=GetNextImageProfile(image);
          if (name == (const char *) NULL)
            break;
          profile=GetImageProfile(image,name);
          if (profile != (StringInfo *) NULL)
          {
            if ((LocaleCompare(name,"ICC") == 0) ||
                (LocaleCompare(name,"ICM") == 0) ||
                (LocaleCompare(name,"IPTC") == 0) ||
                (LocaleCompare(name,"8BIM") == 0) ||
                (LocaleNCompare(name,"gif:",4) == 0))
            {
               size_t
                 length;

               ssize_t
                 offset;

               unsigned char
                 *datum;

               datum=GetStringInfoDatum(profile);
               length=GetStringInfoLength(profile);
               (void) WriteBlobByte(image,(unsigned char) 0x21);
               (void) WriteBlobByte(image,(unsigned char) 0xff);
               (void) WriteBlobByte(image,(unsigned char) 0x0b);
               if ((LocaleCompare(name,"ICC") == 0) ||
                   (LocaleCompare(name,"ICM") == 0))
                 {
                   /*
                     Write ICC extension.
                   */
                   (void) WriteBlob(image,11,(unsigned char *) "ICCRGBG1012");
                   (void) LogMagickEvent(CoderEvent,GetMagickModule(),
                     "  Writing GIF Extension %s","ICCRGBG1012");
                 }
               else
                 if ((LocaleCompare(name,"IPTC") == 0))
                   {
                     /*
                       Write IPTC extension.
                     */
                     (void) WriteBlob(image,11,(unsigned char *) "MGKIPTC0000");
                     (void) LogMagickEvent(CoderEvent,GetMagickModule(),
                       "  Writing GIF Extension %s","MGKIPTC0000");
                   }
                 else
                   if ((LocaleCompare(name,"8BIM") == 0))
                     {
                       /*
                         Write 8BIM extension.
                       */
                        (void) WriteBlob(image,11,(unsigned char *)
                          "MGK8BIM0000");
                        (void) LogMagickEvent(CoderEvent,GetMagickModule(),
                          "  Writing GIF Extension %s","MGK8BIM0000");
                     }
                   else
                     {
                       char
                         extension[MaxTextExtent];

                       /*
                         Write generic extension.
                       */
                       (void) CopyMagickString(extension,name+4,
                         sizeof(extension));
                       (void) WriteBlob(image,11,(unsigned char *) extension);
                       (void) LogMagickEvent(CoderEvent,GetMagickModule(),
                         "  Writing GIF Extension %s",name);
                     }
               offset=0;
               while ((ssize_t) length > offset)
               {
                 size_t
                   block_length;

                 if ((length-offset) < 255)
                   block_length=length-offset;
                 else
                   block_length=255;
                 (void) WriteBlobByte(image,(unsigned char) block_length);
                 (void) WriteBlob(image,(size_t) block_length,datum+offset);
                 offset+=(ssize_t) block_length;
               }
               (void) WriteBlobByte(image,(unsigned char) 0x00);
            }
          }
        }
      }
    (void) WriteBlobByte(image,',');  /* image separator */
    /*
      Write the image header.
    */
    page.x=image->page.x;
    page.y=image->page.y;
    if ((image->page.width != 0) && (image->page.height != 0))
      page=image->page;
    (void) WriteBlobLSBShort(image,(unsigned short) (page.x < 0 ? 0 : page.x));
    (void) WriteBlobLSBShort(image,(unsigned short) (page.y < 0 ? 0 : page.y));
    (void) WriteBlobLSBShort(image,(unsigned short) image->columns);
    (void) WriteBlobLSBShort(image,(unsigned short) image->rows);
    c=0x00;
    if (interlace != NoInterlace)
      c|=0x40;  /* pixel data is interlaced */
    for (j=0; j < (ssize_t) (3*image->colors); j++)
      if (colormap[j] != global_colormap[j])
        break;
    if (j == (ssize_t) (3*image->colors))
      (void) WriteBlobByte(image,(unsigned char) c);
    else
      {
        c|=0x80;
        c|=(bits_per_pixel-1);   /* size of local colormap */
        (void) WriteBlobByte(image,(unsigned char) c);
        length=(size_t) (3*(one << bits_per_pixel));
        (void) WriteBlob(image,length,colormap);
      }
    /*
      Write the image data.
    */
    c=(int) MagickMax(bits_per_pixel,2);
    (void) WriteBlobByte(image,(unsigned char) c);
    status=EncodeImage(write_info,image,(size_t) MagickMax(bits_per_pixel,2)+1);
    if (status == MagickFalse)
      {
        global_colormap=(unsigned char *) RelinquishMagickMemory(
          global_colormap);
        colormap=(unsigned char *) RelinquishMagickMemory(colormap);
        write_info=DestroyImageInfo(write_info);
        ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
      }
    (void) WriteBlobByte(image,(unsigned char) 0x00);
    if (GetNextImageInList(image) == (Image *) NULL)
      break;
    image=SyncNextImageInList(image);
    scene++;
    status=SetImageProgress(image,SaveImagesTag,scene,
      GetImageListLength(image));
    if (status == MagickFalse)
      break;
  } while (write_info->adjoin != MagickFalse);
  (void) WriteBlobByte(image,';'); /* terminator */
  global_colormap=(unsigned char *) RelinquishMagickMemory(global_colormap);
  colormap=(unsigned char *) RelinquishMagickMemory(colormap);
  write_info=DestroyImageInfo(write_info);
  (void) CloseBlob(image);
  return(MagickTrue);
}
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