A question about reading and writing gif image

[sunng1]

hi everyone

I have a GIF image :


It's 27.4KB

My code is :

Code: Select all

int main()
{
	ExceptionInfo * exception = AcquireExceptionInfo();
	ImageInfo *image_info = CloneImageInfo((ImageInfo *) NULL);
	(void) CopyMagickString(image_info->filename, "/root/346889.gif" ,MaxTextExtent);
	Image * image = ReadImage(image_info, exception);
	
	Image * coalImage = CoalesceImages(image, exception);
	
	(void) CopyMagickString(coalImage->filename, "/root/1.gif", MaxTextExtent);
	WriteImage(image_info ,coalImage);
	
	DestroyImages(image);
	DestroyImages(coalImage);
	DestroyImageInfo(image_info);
	DestroyExceptionInfo(exception);
	
	return 0;
｝

the output GIF image is :



It's 271KB

In my code, I used CoalesceImages to get the same size images of te GIF image, and my question is :

How to write a GIF image with the same file size after use CoalesceImages ?

thanks.

[magick]

Use CompareImageLayers().

[sunng1]

I modified the code :

Code: Select all

int main()
{
   ExceptionInfo * exception = AcquireExceptionInfo();
   ImageInfo *image_info = CloneImageInfo((ImageInfo *) NULL);
   (void) CopyMagickString(image_info->filename, "/root/346889.gif" ,MaxTextExtent);
   Image * image = ReadImage(image_info, exception);
   
   Image * coalImage = CoalesceImages(image, exception);
   
    //Image * compImage = CompareImageLayers(coalImage, CompareAnyLayer, exception);
    //Image * compImage = CompareImageLayers(coalImage, CompareClearLayer, exception);
    Image * compImage = CompareImageLayers(coalImage, CompareOverlayLayer, exception);

   
    //(void) CopyMagickString(compImage->filename, "/root/CompareAnyLayer.gif", MaxTextExtent);
    //(void) CopyMagickString(compImage->filename, "/root/CompareClearLayer.gif", MaxTextExtent);
    (void) CopyMagickString(compImage->filename, "/root/CompareOverlayLayer.gif", MaxTextExtent);

    WriteImage(image_info ,compImage);
   
   DestroyImages(image);
   DestroyImages(coalImage);
   DestroyImageInfo(image_info);
   DestroyExceptionInfo(exception);
   
   return 0;
}

Tried all three ImageLayerMethod which CompareImageLayers support, the result is :

CompareAnyLayer


121.8KB
---------------------------------------------------------------------
CompareClearLayer


14.6KB, but ,all frames are the same
---------------------------------------------------------------------
CompareOverlayLayer


121.8KB
---------------------------------------------------------------------

the file size still bigger then the original GIF image, so what can I do?

thanks

[fmw42]

I know very little about gif animations and especially doing them with an API. But you might glean some ideas from Anthony's pages on animations from the command line and especially the one on optimizations at http://www.imagemagick.org/Usage/anim_opt/

Your problem may be one of having more than 256 colors used throughout the full set of images rather than a common set of 256 colors used by every frame.

[anthony]

Actually to do it properly you would use the Optimize Layer Images function.

But I am not certain how it would be called in the C API you are using.

[sunng1]

yeah,

After using OptimizeImageLayers and OptimizeImageTransparency, the file size has down to about 30K,

then after using global color table instead of local color table, the file size has reached the original file size.

thanks, anthony!
thanks, fmw42!
tanks, magick!