Commit message: There is a Division by Zero in function OptimizeLayerFrames (#2743)

in file MagickCore/layer.c. cur->ticks_per_seconds can be zero
with a crafted input argument *image. This is similar to
CVE-2019-13454.
CVE: CVE-2020-27560
CWE: CWE-399
Vulnerability description: ImageMagick 7.0.10-34 allows Division by Zero in OptimizeLayerFrames in MagickCore/layer.c, which may cause a denial of service.

Project: ImageMagick
File: layer.c

MagickExport Image *DisposeImages(const Image *images,ExceptionInfo *exception)
{
  Image
    *dispose_image,
    *dispose_images;

  RectangleInfo
    bounds;

  register Image
    *image,
    *next;

  /*
    Run the image through the animation sequence
  */
  assert(images != (Image *) NULL);
  assert(images->signature == MagickCoreSignature);
  if (images->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",images->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  image=GetFirstImageInList(images);
  dispose_image=CloneImage(image,image->page.width,image->page.height,
    MagickTrue,exception);
  if (dispose_image == (Image *) NULL)
    return((Image *) NULL);
  dispose_image->page=image->page;
  dispose_image->page.x=0;
  dispose_image->page.y=0;
  dispose_image->dispose=NoneDispose;
  dispose_image->background_color.alpha_trait=BlendPixelTrait;
  dispose_image->background_color.alpha=(MagickRealType) TransparentAlpha;
  (void) SetImageBackgroundColor(dispose_image,exception);
  dispose_images=NewImageList();
  for (next=image; image != (Image *) NULL; image=GetNextImageInList(image))
  {
    Image
      *current_image;

    /*
      Overlay this frame's image over the previous disposal image.
    */
    current_image=CloneImage(dispose_image,0,0,MagickTrue,exception);
    if (current_image == (Image *) NULL)
      {
        dispose_images=DestroyImageList(dispose_images);
        dispose_image=DestroyImage(dispose_image);
        return((Image *) NULL);
      }
    current_image->background_color.alpha_trait=BlendPixelTrait;
    (void) CompositeImage(current_image,next,
      next->alpha_trait != UndefinedPixelTrait ? OverCompositeOp : CopyCompositeOp,
      MagickTrue,next->page.x,next->page.y,exception);
    /*
      Handle Background dispose: image is displayed for the delay period.
    */
    if (next->dispose == BackgroundDispose)
      {
        bounds=next->page;
        bounds.width=next->columns;
        bounds.height=next->rows;
        if (bounds.x < 0)
          {
            bounds.width+=bounds.x;
            bounds.x=0;
          }
        if ((ssize_t) (bounds.x+bounds.width) > (ssize_t) current_image->columns)
          bounds.width=current_image->columns-bounds.x;
        if (bounds.y < 0)
          {
            bounds.height+=bounds.y;
            bounds.y=0;
          }
        if ((ssize_t) (bounds.y+bounds.height) > (ssize_t) current_image->rows)
          bounds.height=current_image->rows-bounds.y;
        ClearBounds(current_image,&bounds,exception);
      }
    /*
      Select the appropriate previous/disposed image.
    */
    if (next->dispose == PreviousDispose)
      current_image=DestroyImage(current_image);
    else
      {
        dispose_image=DestroyImage(dispose_image);
        dispose_image=current_image;
        current_image=(Image *) NULL;
      }
    /*
      Save the dispose image just calculated for return.
    */
    {
      Image
        *dispose;

      dispose=CloneImage(dispose_image,0,0,MagickTrue,exception);
      if (dispose == (Image *) NULL)
        {
          dispose_images=DestroyImageList(dispose_images);
          dispose_image=DestroyImage(dispose_image);
          return((Image *) NULL);
        }
      dispose_image->background_color.alpha_trait=BlendPixelTrait;
      (void) CloneImageProfiles(dispose,next);
      (void) CloneImageProperties(dispose,next);
      (void) CloneImageArtifacts(dispose,next);
      dispose->page.x=0;
      dispose->page.y=0;
      dispose->dispose=next->dispose;
      AppendImageToList(&dispose_images,dispose);
    }
  }
  dispose_image=DestroyImage(dispose_image);
  return(GetFirstImageInList(dispose_images));
}

Project: ImageMagick
File: layer.c

MagickExport Image *CompareImagesLayers(const Image *image,
  const LayerMethod method,ExceptionInfo *exception)
{
  Image
    *image_a,
    *image_b,
    *layers;

  RectangleInfo
    *bounds;

  register const Image
    *next;

  register ssize_t
    i;

  assert(image != (const Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  assert((method == CompareAnyLayer) ||
         (method == CompareClearLayer) ||
         (method == CompareOverlayLayer));
  /*
    Allocate bounds memory.
  */
  next=GetFirstImageInList(image);
  bounds=(RectangleInfo *) AcquireQuantumMemory((size_t)
    GetImageListLength(next),sizeof(*bounds));
  if (bounds == (RectangleInfo *) NULL)
    ThrowImageException(ResourceLimitError,"MemoryAllocationFailed");
  /*
    Set up first comparision images.
  */
  image_a=CloneImage(next,next->page.width,next->page.height,
    MagickTrue,exception);
  if (image_a == (Image *) NULL)
    {
      bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
      return((Image *) NULL);
    }
  image_a->background_color.alpha_trait=BlendPixelTrait;
  image_a->background_color.alpha=(MagickRealType) TransparentAlpha;
  (void) SetImageBackgroundColor(image_a,exception);
  image_a->page=next->page;
  image_a->page.x=0;
  image_a->page.y=0;
  (void) CompositeImage(image_a,next,CopyCompositeOp,MagickTrue,next->page.x,
    next->page.y,exception);
  /*
    Compute the bounding box of changes for the later images
  */
  i=0;
  next=GetNextImageInList(next);
  for ( ; next != (const Image *) NULL; next=GetNextImageInList(next))
  {
    image_b=CloneImage(image_a,0,0,MagickTrue,exception);
    if (image_b == (Image *) NULL)
      {
        image_a=DestroyImage(image_a);
        bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
        return((Image *) NULL);
      }
    image_b->background_color.alpha_trait=BlendPixelTrait;
    (void) CompositeImage(image_a,next,CopyCompositeOp,MagickTrue,next->page.x,
      next->page.y,exception);
    bounds[i]=CompareImagesBounds(image_b,image_a,method,exception);
    image_b=DestroyImage(image_b);
    i++;
  }
  image_a=DestroyImage(image_a);
  /*
    Clone first image in sequence.
  */
  next=GetFirstImageInList(image);
  layers=CloneImage(next,0,0,MagickTrue,exception);
  if (layers == (Image *) NULL)
    {
      bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
      return((Image *) NULL);
    }
  layers->background_color.alpha_trait=BlendPixelTrait;
  /*
    Deconstruct the image sequence.
  */
  i=0;
  next=GetNextImageInList(next);
  for ( ; next != (const Image *) NULL; next=GetNextImageInList(next))
  {
    if ((bounds[i].x == -1) && (bounds[i].y == -1) &&
        (bounds[i].width == 1) && (bounds[i].height == 1))
      {
        /*
          An empty frame is returned from CompareImageBounds(), which means the
          current frame is identical to the previous frame.
        */
        i++;
        continue;
      }
    image_a=CloneImage(next,0,0,MagickTrue,exception);
    if (image_a == (Image *) NULL)
      break;
    image_a->background_color.alpha_trait=BlendPixelTrait;
    image_b=CropImage(image_a,&bounds[i],exception);
    image_a=DestroyImage(image_a);
    if (image_b == (Image *) NULL)
      break;
    AppendImageToList(&layers,image_b);
    i++;
  }
  bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
  if (next != (Image *) NULL)
    {
      layers=DestroyImageList(layers);
      return((Image *) NULL);
    }
  return(GetFirstImageInList(layers));
}

Project: ImageMagick
File: layer.c

MagickExport Image *MergeImageLayers(Image *image,const LayerMethod method,
  ExceptionInfo *exception)
{
#define MergeLayersTag  "Merge/Layers"

  Image
    *canvas;

  MagickBooleanType
    proceed;

  RectangleInfo
    page;

  register const Image
    *next;

  size_t
    number_images,
    height,
    width;

  ssize_t
    scene;

  assert(image != (Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  /*
    Determine canvas image size, and its virtual canvas size and offset
  */
  page=image->page;
  width=image->columns;
  height=image->rows;
  switch (method)
  {
    case TrimBoundsLayer:
    case MergeLayer:
    default:
    {
      next=GetNextImageInList(image);
      for ( ; next != (Image *) NULL;  next=GetNextImageInList(next))
      {
        if (page.x > next->page.x)
          {
            width+=page.x-next->page.x;
            page.x=next->page.x;
          }
        if (page.y > next->page.y)
          {
            height+=page.y-next->page.y;
            page.y=next->page.y;
          }
        if ((ssize_t) width < (next->page.x+(ssize_t) next->columns-page.x))
          width=(size_t) next->page.x+(ssize_t) next->columns-page.x;
        if ((ssize_t) height < (next->page.y+(ssize_t) next->rows-page.y))
          height=(size_t) next->page.y+(ssize_t) next->rows-page.y;
      }
      break;
    }
    case FlattenLayer:
    {
      if (page.width > 0)
        width=page.width;
      if (page.height > 0)
        height=page.height;
      page.x=0;
      page.y=0;
      break;
    }
    case MosaicLayer:
    {
      if (page.width > 0)
        width=page.width;
      if (page.height > 0)
        height=page.height;
      for (next=image; next != (Image *) NULL; next=GetNextImageInList(next))
      {
        if (method == MosaicLayer)
          {
            page.x=next->page.x;
            page.y=next->page.y;
            if ((ssize_t) width < (next->page.x+(ssize_t) next->columns))
              width=(size_t) next->page.x+next->columns;
            if ((ssize_t) height < (next->page.y+(ssize_t) next->rows))
              height=(size_t) next->page.y+next->rows;
          }
      }
      page.width=width;
      page.height=height;
      page.x=0;
      page.y=0;
    }
    break;
  }
  /*
    Set virtual canvas size if not defined.
  */
  if (page.width == 0)
    page.width=page.x < 0 ? width : width+page.x;
  if (page.height == 0)
    page.height=page.y < 0 ? height : height+page.y;
  /*
    Handle "TrimBoundsLayer" method separately to normal 'layer merge'.
  */
  if (method == TrimBoundsLayer)
    {
      number_images=GetImageListLength(image);
      for (scene=0; scene < (ssize_t) number_images; scene++)
      {
        image->page.x-=page.x;
        image->page.y-=page.y;
        image->page.width=width;
        image->page.height=height;
        proceed=SetImageProgress(image,MergeLayersTag,(MagickOffsetType) scene,
          number_images);
        if (proceed == MagickFalse)
          break;
        image=GetNextImageInList(image);
        if (image == (Image *) NULL)
          break;
      }
      return((Image *) NULL);
    }
  /*
    Create canvas size of width and height, and background color.
  */
  canvas=CloneImage(image,width,height,MagickTrue,exception);
  if (canvas == (Image *) NULL)
    return((Image *) NULL);
  canvas->background_color.alpha_trait=BlendPixelTrait;
  (void) SetImageBackgroundColor(canvas,exception);
  canvas->page=page;
  canvas->dispose=UndefinedDispose;
  /*
    Compose images onto canvas, with progress monitor
  */
  number_images=GetImageListLength(image);
  for (scene=0; scene < (ssize_t) number_images; scene++)
  {
    (void) CompositeImage(canvas,image,image->compose,MagickTrue,image->page.x-
      canvas->page.x,image->page.y-canvas->page.y,exception);
    proceed=SetImageProgress(image,MergeLayersTag,(MagickOffsetType) scene,
      number_images);
    if (proceed == MagickFalse)
      break;
    image=GetNextImageInList(image);
    if (image == (Image *) NULL)
      break;
  }
  return(canvas);
}

Project: ImageMagick
File: layer.c

static Image *OptimizeLayerFrames(const Image *image,const LayerMethod method,
  ExceptionInfo *exception)
{
  ExceptionInfo
    *sans_exception;

  Image
    *prev_image,
    *dup_image,
    *bgnd_image,
    *optimized_image;

  RectangleInfo
    try_bounds,
    bgnd_bounds,
    dup_bounds,
    *bounds;

  MagickBooleanType
    add_frames,
    try_cleared,
    cleared;

  DisposeType
    *disposals;

  register const Image
    *curr;

  register ssize_t
    i;

  assert(image != (const Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  assert(method == OptimizeLayer ||
         method == OptimizeImageLayer ||
         method == OptimizePlusLayer);
  /*
    Are we allowed to add/remove frames from animation?
  */
  add_frames=method == OptimizePlusLayer ? MagickTrue : MagickFalse;
  /*
    Ensure  all the images are the same size.
  */
  curr=GetFirstImageInList(image);
  for (; curr != (Image *) NULL; curr=GetNextImageInList(curr))
  {
    if ((curr->columns != image->columns) || (curr->rows != image->rows))
      ThrowImageException(OptionError,"ImagesAreNotTheSameSize");

    if ((curr->page.x != 0) || (curr->page.y != 0) ||
        (curr->page.width != image->page.width) ||
        (curr->page.height != image->page.height))
      ThrowImageException(OptionError,"ImagePagesAreNotCoalesced");
  }
  /*
    Allocate memory (times 2 if we allow the use of frame duplications)
  */
  curr=GetFirstImageInList(image);
  bounds=(RectangleInfo *) AcquireQuantumMemory((size_t)
    GetImageListLength(curr),(add_frames != MagickFalse ? 2UL : 1UL)*
    sizeof(*bounds));
  if (bounds == (RectangleInfo *) NULL)
    ThrowImageException(ResourceLimitError,"MemoryAllocationFailed");
  disposals=(DisposeType *) AcquireQuantumMemory((size_t)
    GetImageListLength(image),(add_frames != MagickFalse ? 2UL : 1UL)*
    sizeof(*disposals));
  if (disposals == (DisposeType *) NULL)
    {
      bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
      ThrowImageException(ResourceLimitError,"MemoryAllocationFailed");
    }
  /*
    Initialise Previous Image as fully transparent
  */
  prev_image=CloneImage(curr,curr->columns,curr->rows,MagickTrue,exception);
  if (prev_image == (Image *) NULL)
    {
      bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
      disposals=(DisposeType *) RelinquishMagickMemory(disposals);
      return((Image *) NULL);
    }
  prev_image->page=curr->page;  /* ERROR: <-- should not be need, but is! */
  prev_image->page.x=0;
  prev_image->page.y=0;
  prev_image->dispose=NoneDispose;
  prev_image->background_color.alpha_trait=BlendPixelTrait;
  prev_image->background_color.alpha=(MagickRealType) TransparentAlpha;
  (void) SetImageBackgroundColor(prev_image,exception);
  /*
    Figure out the area of overlay of the first frame
    No pixel could be cleared as all pixels are already cleared.
  */
#if DEBUG_OPT_FRAME
  i=0;
  (void) FormatLocaleFile(stderr,"frame %.20g :-\n",(double) i);
#endif
  disposals[0]=NoneDispose;
  bounds[0]=CompareImagesBounds(prev_image,curr,CompareAnyLayer,exception);
#if DEBUG_OPT_FRAME
  (void) FormatLocaleFile(stderr, "overlay: %.20gx%.20g%+.20g%+.20g\n\n",
    (double) bounds[i].width,(double) bounds[i].height,
    (double) bounds[i].x,(double) bounds[i].y );
#endif
  /*
    Compute the bounding box of changes for each pair of images.
  */
  i=1;
  bgnd_image=(Image *) NULL;
  dup_image=(Image *) NULL;
  dup_bounds.width=0;
  dup_bounds.height=0;
  dup_bounds.x=0;
  dup_bounds.y=0;
  curr=GetNextImageInList(curr);
  for ( ; curr != (const Image *) NULL; curr=GetNextImageInList(curr))
  {
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr,"frame %.20g :-\n",(double) i);
#endif
    /*
      Assume none disposal is the best
    */
    bounds[i]=CompareImagesBounds(curr->previous,curr,CompareAnyLayer,exception);
    cleared=IsBoundsCleared(curr->previous,curr,&bounds[i],exception);
    disposals[i-1]=NoneDispose;
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr, "overlay: %.20gx%.20g%+.20g%+.20g%s%s\n",
         (double) bounds[i].width,(double) bounds[i].height,
         (double) bounds[i].x,(double) bounds[i].y,
         bounds[i].x < 0?"  (unchanged)":"",
         cleared?"  (pixels cleared)":"");
#endif
    if ( bounds[i].x < 0 ) {
      /*
        Image frame is exactly the same as the previous frame!
        If not adding frames leave it to be cropped down to a null image.
        Otherwise mark previous image for deleted, transfering its crop bounds
        to the current image.
      */
      if ( add_frames && i>=2 ) {
        disposals[i-1]=DelDispose;
        disposals[i]=NoneDispose;
        bounds[i]=bounds[i-1];
        i++;
        continue;
      }
    }
    else
      {
        /*
          Compare a none disposal against a previous disposal
        */
        try_bounds=CompareImagesBounds(prev_image,curr,CompareAnyLayer,exception);
        try_cleared=IsBoundsCleared(prev_image,curr,&try_bounds,exception);
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr, "test_prev: %.20gx%.20g%+.20g%+.20g%s\n",
         (double) try_bounds.width,(double) try_bounds.height,
         (double) try_bounds.x,(double) try_bounds.y,
         try_cleared?"  (pixels were cleared)":"");
#endif
        if ( (!try_cleared && cleared ) ||
                try_bounds.width * try_bounds.height
                    <  bounds[i].width * bounds[i].height )
          {
            cleared=try_cleared;
            bounds[i]=try_bounds;
            disposals[i-1]=PreviousDispose;
#if DEBUG_OPT_FRAME
            (void) FormatLocaleFile(stderr,"previous: accepted\n");
          } else {
            (void) FormatLocaleFile(stderr,"previous: rejected\n");
#endif
          }

        /*
          If we are allowed lets try a complex frame duplication.
          It is useless if the previous image already clears pixels correctly.
          This method will always clear all the pixels that need to be cleared.
        */
        dup_bounds.width=dup_bounds.height=0; /* no dup, no pixel added */
        if ( add_frames )
          {
            dup_image=CloneImage(curr->previous,0,0,MagickTrue,exception);
            if (dup_image == (Image *) NULL)
              {
                bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
                disposals=(DisposeType *) RelinquishMagickMemory(disposals);
                prev_image=DestroyImage(prev_image);
                return((Image *) NULL);
              }
            dup_image->background_color.alpha_trait=BlendPixelTrait;
            dup_bounds=CompareImagesBounds(dup_image,curr,CompareClearLayer,exception);
            ClearBounds(dup_image,&dup_bounds,exception);
            try_bounds=CompareImagesBounds(dup_image,curr,CompareAnyLayer,exception);
            if ( cleared ||
                   dup_bounds.width*dup_bounds.height
                      +try_bounds.width*try_bounds.height
                   < bounds[i].width * bounds[i].height )
              {
                cleared=MagickFalse;
                bounds[i]=try_bounds;
                disposals[i-1]=DupDispose;
                /* to be finalised later, if found to be optimial */
              }
            else
              dup_bounds.width=dup_bounds.height=0;
          }
        /*
          Now compare against a simple background disposal
        */
        bgnd_image=CloneImage(curr->previous,0,0,MagickTrue,exception);
        if (bgnd_image == (Image *) NULL)
          {
            bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
            disposals=(DisposeType *) RelinquishMagickMemory(disposals);
            prev_image=DestroyImage(prev_image);
            if ( dup_image != (Image *) NULL)
              dup_image=DestroyImage(dup_image);
            return((Image *) NULL);
          }
        bgnd_image->background_color.alpha_trait=BlendPixelTrait;
        bgnd_bounds=bounds[i-1]; /* interum bounds of the previous image */
        ClearBounds(bgnd_image,&bgnd_bounds,exception);
        try_bounds=CompareImagesBounds(bgnd_image,curr,CompareAnyLayer,exception);
        try_cleared=IsBoundsCleared(bgnd_image,curr,&try_bounds,exception);
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr, "background: %s\n",
         try_cleared?"(pixels cleared)":"");
#endif
        if ( try_cleared )
          {
            /*
              Straight background disposal failed to clear pixels needed!
              Lets try expanding the disposal area of the previous frame, to
              include the pixels that are cleared.  This guaranteed
              to work, though may not be the most optimized solution.
            */
            try_bounds=CompareImagesBounds(curr->previous,curr,CompareClearLayer,exception);
#if DEBUG_OPT_FRAME
            (void) FormatLocaleFile(stderr, "expand_clear: %.20gx%.20g%+.20g%+.20g%s\n",
                (double) try_bounds.width,(double) try_bounds.height,
                (double) try_bounds.x,(double) try_bounds.y,
                try_bounds.x<0?"  (no expand nessary)":"");
#endif
            if ( bgnd_bounds.x < 0 )
              bgnd_bounds = try_bounds;
            else
              {
#if DEBUG_OPT_FRAME
                (void) FormatLocaleFile(stderr, "expand_bgnd: %.20gx%.20g%+.20g%+.20g\n",
                    (double) bgnd_bounds.width,(double) bgnd_bounds.height,
                    (double) bgnd_bounds.x,(double) bgnd_bounds.y );
#endif
                if ( try_bounds.x < bgnd_bounds.x )
                  {
                     bgnd_bounds.width+= bgnd_bounds.x-try_bounds.x;
                     if ( bgnd_bounds.width < try_bounds.width )
                       bgnd_bounds.width = try_bounds.width;
                     bgnd_bounds.x = try_bounds.x;
                  }
                else
                  {
                     try_bounds.width += try_bounds.x - bgnd_bounds.x;
                     if ( bgnd_bounds.width < try_bounds.width )
                       bgnd_bounds.width = try_bounds.width;
                  }
                if ( try_bounds.y < bgnd_bounds.y )
                  {
                     bgnd_bounds.height += bgnd_bounds.y - try_bounds.y;
                     if ( bgnd_bounds.height < try_bounds.height )
                       bgnd_bounds.height = try_bounds.height;
                     bgnd_bounds.y = try_bounds.y;
                  }
                else
                  {
                    try_bounds.height += try_bounds.y - bgnd_bounds.y;
                     if ( bgnd_bounds.height < try_bounds.height )
                       bgnd_bounds.height = try_bounds.height;
                  }
#if DEBUG_OPT_FRAME
                (void) FormatLocaleFile(stderr, "        to : %.20gx%.20g%+.20g%+.20g\n",
                    (double) bgnd_bounds.width,(double) bgnd_bounds.height,
                    (double) bgnd_bounds.x,(double) bgnd_bounds.y );
#endif
              }
            ClearBounds(bgnd_image,&bgnd_bounds,exception);
#if DEBUG_OPT_FRAME
/* Something strange is happening with a specific animation
 * CompareAnyLayers (normal method) and CompareClearLayers returns the whole
 * image, which is not posibly correct!  As verified by previous tests.
 * Something changed beyond the bgnd_bounds clearing.  But without being able
 * to see, or writet he image at this point it is hard to tell what is wrong!
 * Only CompareOverlay seemed to return something sensible.
 */
            try_bounds=CompareImagesBounds(bgnd_image,curr,CompareClearLayer,exception);
            (void) FormatLocaleFile(stderr, "expand_ctst: %.20gx%.20g%+.20g%+.20g\n",
                (double) try_bounds.width,(double) try_bounds.height,
                (double) try_bounds.x,(double) try_bounds.y );
            try_bounds=CompareImagesBounds(bgnd_image,curr,CompareAnyLayer,exception);
            try_cleared=IsBoundsCleared(bgnd_image,curr,&try_bounds,exception);
            (void) FormatLocaleFile(stderr, "expand_any : %.20gx%.20g%+.20g%+.20g%s\n",
                (double) try_bounds.width,(double) try_bounds.height,
                (double) try_bounds.x,(double) try_bounds.y,
                try_cleared?"   (pixels cleared)":"");
#endif
            try_bounds=CompareImagesBounds(bgnd_image,curr,CompareOverlayLayer,exception);
#if DEBUG_OPT_FRAME
            try_cleared=IsBoundsCleared(bgnd_image,curr,&try_bounds,exception);
            (void) FormatLocaleFile(stderr, "expand_test: %.20gx%.20g%+.20g%+.20g%s\n",
                (double) try_bounds.width,(double) try_bounds.height,
                (double) try_bounds.x,(double) try_bounds.y,
                try_cleared?"   (pixels cleared)":"");
#endif
          }
        /*
          Test if this background dispose is smaller than any of the
          other methods we tryed before this (including duplicated frame)
        */
        if ( cleared ||
              bgnd_bounds.width*bgnd_bounds.height
                +try_bounds.width*try_bounds.height
              < bounds[i-1].width*bounds[i-1].height
                  +dup_bounds.width*dup_bounds.height
                  +bounds[i].width*bounds[i].height )
          {
            cleared=MagickFalse;
            bounds[i-1]=bgnd_bounds;
            bounds[i]=try_bounds;
            if ( disposals[i-1] == DupDispose )
              dup_image=DestroyImage(dup_image);
            disposals[i-1]=BackgroundDispose;
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr,"expand_bgnd: accepted\n");
          } else {
    (void) FormatLocaleFile(stderr,"expand_bgnd: reject\n");
#endif
          }
      }
    /*
       Finalise choice of dispose, set new prev_image,
       and junk any extra images as appropriate,
    */
    if ( disposals[i-1] == DupDispose )
      {
         if (bgnd_image != (Image *) NULL)
           bgnd_image=DestroyImage(bgnd_image);
         prev_image=DestroyImage(prev_image);
         prev_image=dup_image, dup_image=(Image *) NULL;
         bounds[i+1]=bounds[i];
         bounds[i]=dup_bounds;
         disposals[i-1]=DupDispose;
         disposals[i]=BackgroundDispose;
         i++;
      }
    else
      {
        if ( dup_image != (Image *) NULL)
          dup_image=DestroyImage(dup_image);
        if ( disposals[i-1] != PreviousDispose )
          prev_image=DestroyImage(prev_image);
        if ( disposals[i-1] == BackgroundDispose )
          prev_image=bgnd_image, bgnd_image=(Image *) NULL;
        if (bgnd_image != (Image *) NULL)
          bgnd_image=DestroyImage(bgnd_image);
        if ( disposals[i-1] == NoneDispose )
          {
            prev_image=ReferenceImage(curr->previous);
            if (prev_image == (Image *) NULL)
              {
                bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
                disposals=(DisposeType *) RelinquishMagickMemory(disposals);
                return((Image *) NULL);
              }
          }

      }
    assert(prev_image != (Image *) NULL);
    disposals[i]=disposals[i-1];
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr, "final   %.20g : %s  %.20gx%.20g%+.20g%+.20g\n",
         (double) i-1,
         CommandOptionToMnemonic(MagickDisposeOptions,disposals[i-1]),
         (double) bounds[i-1].width,(double) bounds[i-1].height,
         (double) bounds[i-1].x,(double) bounds[i-1].y );
#endif
#if DEBUG_OPT_FRAME
    (void) FormatLocaleFile(stderr, "interum %.20g : %s  %.20gx%.20g%+.20g%+.20g\n",
         (double) i,
         CommandOptionToMnemonic(MagickDisposeOptions,disposals[i]),
         (double) bounds[i].width,(double) bounds[i].height,
         (double) bounds[i].x,(double) bounds[i].y );
    (void) FormatLocaleFile(stderr,"\n");
#endif
    i++;
  }
  prev_image=DestroyImage(prev_image);
  /*
    Optimize all images in sequence.
  */
  sans_exception=AcquireExceptionInfo();
  i=0;
  curr=GetFirstImageInList(image);
  optimized_image=NewImageList();
  while ( curr != (const Image *) NULL )
  {
    prev_image=CloneImage(curr,0,0,MagickTrue,exception);
    if (prev_image == (Image *) NULL)
      break;
    prev_image->background_color.alpha_trait=BlendPixelTrait;
    if ( disposals[i] == DelDispose ) {
      size_t time = 0;
      while ( disposals[i] == DelDispose ) {
        time +=(size_t) (curr->delay*1000*
          PerceptibleReciprocal((double) curr->ticks_per_second));
        curr=GetNextImageInList(curr);
        i++;
      }
      time += (size_t)(curr->delay*1000*
        PerceptibleReciprocal((double) curr->ticks_per_second));
      prev_image->ticks_per_second = 100L;
      prev_image->delay = time*prev_image->ticks_per_second/1000;
    }
    bgnd_image=CropImage(prev_image,&bounds[i],sans_exception);
    prev_image=DestroyImage(prev_image);
    if (bgnd_image == (Image *) NULL)
      break;
    bgnd_image->dispose=disposals[i];
    if ( disposals[i] == DupDispose ) {
      bgnd_image->delay=0;
      bgnd_image->dispose=NoneDispose;
    }
    else
      curr=GetNextImageInList(curr);
    AppendImageToList(&optimized_image,bgnd_image);
    i++;
  }
  sans_exception=DestroyExceptionInfo(sans_exception);
  bounds=(RectangleInfo *) RelinquishMagickMemory(bounds);
  disposals=(DisposeType *) RelinquishMagickMemory(disposals);
  if (curr != (Image *) NULL)
    {
      optimized_image=DestroyImageList(optimized_image);
      return((Image *) NULL);
    }
  return(GetFirstImageInList(optimized_image));
}

Project: ImageMagick
File: layer.c

static MagickBooleanType IsBoundsCleared(const Image *image1,
  const Image *image2,RectangleInfo *bounds,ExceptionInfo *exception)
{
  register const Quantum
    *p,
    *q;

  register ssize_t
    x;

  ssize_t
    y;

  if (bounds->x < 0)
    return(MagickFalse);
  for (y=0; y < (ssize_t) bounds->height; y++)
  {
    p=GetVirtualPixels(image1,bounds->x,bounds->y+y,bounds->width,1,exception);
    q=GetVirtualPixels(image2,bounds->x,bounds->y+y,bounds->width,1,exception);
    if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL))
      break;
    for (x=0; x < (ssize_t) bounds->width; x++)
    {
      if ((GetPixelAlpha(image1,p) >= (Quantum) (QuantumRange/2)) &&
          (GetPixelAlpha(image2,q) < (Quantum) (QuantumRange/2)))
        break;
      p+=GetPixelChannels(image1);
      q+=GetPixelChannels(image2);
    }
    if (x < (ssize_t) bounds->width)
      break;
  }
  return(y < (ssize_t) bounds->height ? MagickTrue : MagickFalse);
}

Project: ImageMagick
File: layer.c

static MagickBooleanType ComparePixels(const LayerMethod method,
  const PixelInfo *p,const PixelInfo *q)
{
  double
    o1,
    o2;

  /*
    Any change in pixel values
  */
  if (method == CompareAnyLayer)
    return(IsFuzzyEquivalencePixelInfo(p,q) == MagickFalse ? MagickTrue : MagickFalse);
  o1 = (p->alpha_trait != UndefinedPixelTrait) ? p->alpha : OpaqueAlpha;
  o2 = (q->alpha_trait != UndefinedPixelTrait) ? q->alpha : OpaqueAlpha;
  /*
    Pixel goes from opaque to transprency.
  */
  if (method == CompareClearLayer)
    return((MagickBooleanType) ( (o1 >= ((double) QuantumRange/2.0)) &&
      (o2 < ((double) QuantumRange/2.0)) ) );
  /*
    Overlay would change first pixel by second.
  */
  if (method == CompareOverlayLayer)
    {
      if (o2 < ((double) QuantumRange/2.0))
        return MagickFalse;
      return(IsFuzzyEquivalencePixelInfo(p,q) == MagickFalse ? MagickTrue :
        MagickFalse);
    }
  return(MagickFalse);
}

Project: ImageMagick
File: layer.c

static RectangleInfo CompareImagesBounds(const Image *image1,
  const Image *image2,const LayerMethod method,ExceptionInfo *exception)
{
  RectangleInfo
    bounds;

  PixelInfo
    pixel1,
    pixel2;

  register const Quantum
    *p,
    *q;

  register ssize_t
    x;

  ssize_t
    y;

  /*
    Set bounding box of the differences between images.
  */
  GetPixelInfo(image1,&pixel1);
  GetPixelInfo(image2,&pixel2);
  for (x=0; x < (ssize_t) image1->columns; x++)
  {
    p=GetVirtualPixels(image1,x,0,1,image1->rows,exception);
    q=GetVirtualPixels(image2,x,0,1,image2->rows,exception);
    if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL))
      break;
    for (y=0; y < (ssize_t) image1->rows; y++)
    {
      GetPixelInfoPixel(image1,p,&pixel1);
      GetPixelInfoPixel(image2,q,&pixel2);
      if (ComparePixels(method,&pixel1,&pixel2) != MagickFalse)
        break;
      p+=GetPixelChannels(image1);
      q+=GetPixelChannels(image2);
    }
    if (y < (ssize_t) image1->rows)
      break;
  }
  if (x >= (ssize_t) image1->columns)
    {
      /*
        Images are identical, return a null image.
      */
      bounds.x=-1;
      bounds.y=-1;
      bounds.width=1;
      bounds.height=1;
      return(bounds);
    }
  bounds.x=x;
  for (x=(ssize_t) image1->columns-1; x >= 0; x--)
  {
    p=GetVirtualPixels(image1,x,0,1,image1->rows,exception);
    q=GetVirtualPixels(image2,x,0,1,image2->rows,exception);
    if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL))
      break;
    for (y=0; y < (ssize_t) image1->rows; y++)
    {
      GetPixelInfoPixel(image1,p,&pixel1);
      GetPixelInfoPixel(image2,q,&pixel2);
      if (ComparePixels(method,&pixel1,&pixel2) != MagickFalse)
        break;
      p+=GetPixelChannels(image1);
      q+=GetPixelChannels(image2);
    }
    if (y < (ssize_t) image1->rows)
      break;
  }
  bounds.width=(size_t) (x-bounds.x+1);
  for (y=0; y < (ssize_t) image1->rows; y++)
  {
    p=GetVirtualPixels(image1,0,y,image1->columns,1,exception);
    q=GetVirtualPixels(image2,0,y,image2->columns,1,exception);
    if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL))
      break;
    for (x=0; x < (ssize_t) image1->columns; x++)
    {
      GetPixelInfoPixel(image1,p,&pixel1);
      GetPixelInfoPixel(image2,q,&pixel2);
      if (ComparePixels(method,&pixel1,&pixel2) != MagickFalse)
        break;
      p+=GetPixelChannels(image1);
      q+=GetPixelChannels(image2);
    }
    if (x < (ssize_t) image1->columns)
      break;
  }
  bounds.y=y;
  for (y=(ssize_t) image1->rows-1; y >= 0; y--)
  {
    p=GetVirtualPixels(image1,0,y,image1->columns,1,exception);
    q=GetVirtualPixels(image2,0,y,image2->columns,1,exception);
    if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL))
      break;
    for (x=0; x < (ssize_t) image1->columns; x++)
    {
      GetPixelInfoPixel(image1,p,&pixel1);
      GetPixelInfoPixel(image2,q,&pixel2);
      if (ComparePixels(method,&pixel1,&pixel2) != MagickFalse)
        break;
      p+=GetPixelChannels(image1);
      q+=GetPixelChannels(image2);
    }
    if (x < (ssize_t) image1->columns)
      break;
  }
  bounds.height=(size_t) (y-bounds.y+1);
  return(bounds);
}

Project: ImageMagick
File: layer.c

MagickExport void OptimizeImageTransparency(const Image *image,
     ExceptionInfo *exception)
{
  Image
    *dispose_image;

  register Image
    *next;

  /*
    Run the image through the animation sequence
  */
  assert(image != (Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  next=GetFirstImageInList(image);
  dispose_image=CloneImage(next,next->page.width,next->page.height,
    MagickTrue,exception);
  if (dispose_image == (Image *) NULL)
    return;
  dispose_image->page=next->page;
  dispose_image->page.x=0;
  dispose_image->page.y=0;
  dispose_image->dispose=NoneDispose;
  dispose_image->background_color.alpha_trait=BlendPixelTrait;
  dispose_image->background_color.alpha=(MagickRealType) TransparentAlpha;
  (void) SetImageBackgroundColor(dispose_image,exception);

  while ( next != (Image *) NULL )
  {
    Image
      *current_image;

    /*
      Overlay this frame's image over the previous disposal image
    */
    current_image=CloneImage(dispose_image,0,0,MagickTrue,exception);
    if (current_image == (Image *) NULL)
      {
        dispose_image=DestroyImage(dispose_image);
        return;
      }
    current_image->background_color.alpha_trait=BlendPixelTrait;
    (void) CompositeImage(current_image,next,next->alpha_trait != UndefinedPixelTrait ?
      OverCompositeOp : CopyCompositeOp,MagickTrue,next->page.x,next->page.y,
      exception);
    /*
      At this point the image would be displayed, for the delay period
    **
      Work out the disposal of the previous image
    */
    if (next->dispose == BackgroundDispose)
      {
        RectangleInfo
          bounds=next->page;

        bounds.width=next->columns;
        bounds.height=next->rows;
        if (bounds.x < 0)
          {
            bounds.width+=bounds.x;
            bounds.x=0;
          }
        if ((ssize_t) (bounds.x+bounds.width) > (ssize_t) current_image->columns)
          bounds.width=current_image->columns-bounds.x;
        if (bounds.y < 0)
          {
            bounds.height+=bounds.y;
            bounds.y=0;
          }
        if ((ssize_t) (bounds.y+bounds.height) > (ssize_t) current_image->rows)
          bounds.height=current_image->rows-bounds.y;
        ClearBounds(current_image,&bounds,exception);
      }
    if (next->dispose != PreviousDispose)
      {
        dispose_image=DestroyImage(dispose_image);
        dispose_image=current_image;
      }
    else
      current_image=DestroyImage(current_image);

    /*
      Optimize Transparency of the next frame (if present)
    */
    next=GetNextImageInList(next);
    if (next != (Image *) NULL) {
      (void) CompositeImage(next,dispose_image,ChangeMaskCompositeOp,
        MagickTrue,-(next->page.x),-(next->page.y),exception);
    }
  }
  dispose_image=DestroyImage(dispose_image);
  return;
}

Project: ImageMagick
File: layer.c

static inline void CompositeCanvas(Image *destination,
  const CompositeOperator compose,Image *source,ssize_t x_offset,
  ssize_t y_offset,ExceptionInfo *exception)
{
  const char
    *value;

  x_offset+=source->page.x-destination->page.x;
  y_offset+=source->page.y-destination->page.y;
  value=GetImageArtifact(source,"compose:outside-overlay");
  (void) CompositeImage(destination,source,compose,
    (value != (const char *) NULL) && (IsStringTrue(value) != MagickFalse) ?
    MagickFalse : MagickTrue,x_offset,y_offset,exception);
}

Project: ImageMagick
File: layer.c

MagickExport void CompositeLayers(Image *destination,
  const CompositeOperator compose, Image *source,const ssize_t x_offset,
  const ssize_t y_offset,ExceptionInfo *exception)
{
  assert(destination != (Image *) NULL);
  assert(destination->signature == MagickCoreSignature);
  assert(source != (Image *) NULL);
  assert(source->signature == MagickCoreSignature);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  if (source->debug != MagickFalse || destination->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s - %s",
      source->filename,destination->filename);

  /*
    Overlay single source image over destation image/list
  */
  if ( source->next == (Image *) NULL )
    while ( destination != (Image *) NULL )
    {
      CompositeCanvas(destination, compose, source, x_offset, y_offset,
        exception);
      destination=GetNextImageInList(destination);
    }

  /*
    Overlay source image list over single destination.
    Multiple clones of destination image are created to match source list.
    Original Destination image becomes first image of generated list.
    As such the image list pointer does not require any change in caller.
    Some animation attributes however also needs coping in this case.
  */
  else if ( destination->next == (Image *) NULL )
  {
    Image *dest = CloneImage(destination,0,0,MagickTrue,exception);

    if (dest != (Image *) NULL)
      {
        dest->background_color.alpha_trait=BlendPixelTrait;
        CompositeCanvas(destination, compose, source, x_offset, y_offset,
          exception);
        /* copy source image attributes ? */
        if ( source->next != (Image *) NULL )
          {
            destination->delay=source->delay;
            destination->iterations=source->iterations;
          }
        source=GetNextImageInList(source);
        while (source != (Image *) NULL)
        {
          AppendImageToList(&destination,
            CloneImage(dest,0,0,MagickTrue,exception));
          destination->background_color.alpha_trait=BlendPixelTrait;
          destination=GetLastImageInList(destination);
          CompositeCanvas(destination,compose,source,x_offset,y_offset,
            exception);
          destination->delay=source->delay;
          destination->iterations=source->iterations;
          source=GetNextImageInList(source);
        }
        dest=DestroyImage(dest);
      }
  }

  /*
    Overlay a source image list over a destination image list
    until either list runs out of images. (Does not repeat)
  */
  else
    while ( source != (Image *) NULL && destination != (Image *) NULL )
    {
      CompositeCanvas(destination, compose, source, x_offset, y_offset,
        exception);
      source=GetNextImageInList(source);
      destination=GetNextImageInList(destination);
    }
}

Project: ImageMagick
File: layer.c

MagickExport Image *CoalesceImages(const Image *image,ExceptionInfo *exception)
{
  Image
    *coalesce_image,
    *dispose_image,
    *previous;

  register Image
    *next;

  RectangleInfo
    bounds;

  /*
    Coalesce the image sequence.
  */
  assert(image != (Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  next=GetFirstImageInList(image);
  bounds=next->page;
  if (bounds.width == 0)
    {
      bounds.width=next->columns;
      if (bounds.x > 0)
        bounds.width+=bounds.x;
    }
  if (bounds.height == 0)
    {
      bounds.height=next->rows;
      if (bounds.y > 0)
        bounds.height+=bounds.y;
    }
  bounds.x=0;
  bounds.y=0;
  coalesce_image=CloneImage(next,bounds.width,bounds.height,MagickTrue,
    exception);
  if (coalesce_image == (Image *) NULL)
    return((Image *) NULL);
  coalesce_image->background_color.alpha_trait=BlendPixelTrait;
  coalesce_image->background_color.alpha=(MagickRealType) TransparentAlpha;
  (void) SetImageBackgroundColor(coalesce_image,exception);
  coalesce_image->alpha_trait=next->alpha_trait;
  coalesce_image->page=bounds;
  coalesce_image->dispose=NoneDispose;
  /*
    Coalesce rest of the images.
  */
  dispose_image=CloneImage(coalesce_image,0,0,MagickTrue,exception);
  if (dispose_image == (Image *) NULL)
    {
      coalesce_image=DestroyImage(coalesce_image);
      return((Image *) NULL);
    }
  dispose_image->background_color.alpha_trait=BlendPixelTrait;
  (void) CompositeImage(coalesce_image,next,CopyCompositeOp,MagickTrue,
    next->page.x,next->page.y,exception);
  next=GetNextImageInList(next);
  for ( ; next != (Image *) NULL; next=GetNextImageInList(next))
  {
    const char
      *attribute;

    /*
      Determine the bounds that was overlaid in the previous image.
    */
    previous=GetPreviousImageInList(next);
    bounds=previous->page;
    bounds.width=previous->columns;
    bounds.height=previous->rows;
    if (bounds.x < 0)
      {
        bounds.width+=bounds.x;
        bounds.x=0;
      }
    if ((ssize_t) (bounds.x+bounds.width) > (ssize_t) coalesce_image->columns)
      bounds.width=coalesce_image->columns-bounds.x;
    if (bounds.y < 0)
      {
        bounds.height+=bounds.y;
        bounds.y=0;
      }
    if ((ssize_t) (bounds.y+bounds.height) > (ssize_t) coalesce_image->rows)
      bounds.height=coalesce_image->rows-bounds.y;
    /*
      Replace the dispose image with the new coalesced image.
    */
    if (GetPreviousImageInList(next)->dispose != PreviousDispose)
      {
        dispose_image=DestroyImage(dispose_image);
        dispose_image=CloneImage(coalesce_image,0,0,MagickTrue,exception);
        if (dispose_image == (Image *) NULL)
          {
            coalesce_image=DestroyImageList(coalesce_image);
            return((Image *) NULL);
          }
        dispose_image->background_color.alpha_trait=BlendPixelTrait;
      }
    /*
      Clear the overlaid area of the coalesced bounds for background disposal
    */
    if (next->previous->dispose == BackgroundDispose)
      ClearBounds(dispose_image,&bounds,exception);
    /*
      Next image is the dispose image, overlaid with next frame in sequence.
    */
    coalesce_image->next=CloneImage(dispose_image,0,0,MagickTrue,exception);
    coalesce_image->next->previous=coalesce_image;
    previous=coalesce_image;
    coalesce_image=GetNextImageInList(coalesce_image);
    coalesce_image->background_color.alpha_trait=BlendPixelTrait;
    attribute=GetImageProperty(next,"webp:mux-blend",exception);
    if (attribute == (const char *) NULL)
      (void) CompositeImage(coalesce_image,next,
        next->alpha_trait != UndefinedPixelTrait ? OverCompositeOp :
        CopyCompositeOp,MagickTrue,next->page.x,next->page.y,exception);
    else
      (void) CompositeImage(coalesce_image,next,
        LocaleCompare(attribute,"AtopBackgroundAlphaBlend") == 0 ?
        OverCompositeOp : CopyCompositeOp,MagickTrue,next->page.x,next->page.y,
        exception);
    (void) CloneImageProfiles(coalesce_image,next);
    (void) CloneImageProperties(coalesce_image,next);
    (void) CloneImageArtifacts(coalesce_image,next);
    coalesce_image->page=previous->page;
    /*
      If a pixel goes opaque to transparent, use background dispose.
    */
    if (IsBoundsCleared(previous,coalesce_image,&bounds,exception) != MagickFalse)
      coalesce_image->dispose=BackgroundDispose;
    else
      coalesce_image->dispose=NoneDispose;
    previous->dispose=coalesce_image->dispose;
  }
  dispose_image=DestroyImage(dispose_image);
  return(GetFirstImageInList(coalesce_image));
}

Project: ImageMagick
File: layer.c

MagickExport void RemoveDuplicateLayers(Image **images,ExceptionInfo *exception)
{
  RectangleInfo
    bounds;

  register Image
    *image,
    *next;

  assert((*images) != (const Image *) NULL);
  assert((*images)->signature == MagickCoreSignature);
  if ((*images)->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",
      (*images)->filename);
  assert(exception != (ExceptionInfo *) NULL);
  assert(exception->signature == MagickCoreSignature);
  image=GetFirstImageInList(*images);
  for ( ; (next=GetNextImageInList(image)) != (Image *) NULL; image=next)
  {
    if ((image->columns != next->columns) || (image->rows != next->rows) ||
        (image->page.x != next->page.x) || (image->page.y != next->page.y))
      continue;
    bounds=CompareImagesBounds(image,next,CompareAnyLayer,exception);
    if (bounds.x < 0)
      {
        /*
          Two images are the same, merge time delays and delete one.
        */
        size_t
          time;

        time=(size_t) (1000.0*image->delay*
          PerceptibleReciprocal((double) image->ticks_per_second));
        time+=(size_t) (1000.0*next->delay*
          PerceptibleReciprocal((double) next->ticks_per_second));
        next->ticks_per_second=100L;
        next->delay=time*image->ticks_per_second/1000;
        next->iterations=image->iterations;
        *images=image;
        (void) DeleteImageFromList(images);
      }
  }
  *images=GetFirstImageInList(*images);
}

Project: ImageMagick
File: layer.c

static void ClearBounds(Image *image,RectangleInfo *bounds,
  ExceptionInfo *exception)
{
  ssize_t
    y;

  if (bounds->x < 0)
    return;
  if (image->alpha_trait == UndefinedPixelTrait)
    (void) SetImageAlphaChannel(image,OpaqueAlphaChannel,exception);
  for (y=0; y < (ssize_t) bounds->height; y++)
  {
    register ssize_t
      x;

    register Quantum
      *magick_restrict q;

    q=GetAuthenticPixels(image,bounds->x,bounds->y+y,bounds->width,1,exception);
    if (q == (Quantum *) NULL)
      break;
    for (x=0; x < (ssize_t) bounds->width; x++)
    {
      SetPixelAlpha(image,TransparentAlpha,q);
      q+=GetPixelChannels(image);
    }
    if (SyncAuthenticPixels(image,exception) == MagickFalse)
      break;
  }
}