How do I get the RGB colour data from a GIFLIB SavedImage structure

Question

I'm using GIFLIB to load in a gif file and I want to extract the RGB data from each frame.

I've used DGifSlurp to load in the file but I cant work out exactly how to get the RGB data from the SavedImage structure. Two tests seem to work, though I've guessed how to do it, but a third crashes with a memory exception. Is there a function in the library I should be using, or is there simple code ?

void    TestGIF()
{
    int error=0;
    GifFileType * gif=DGifOpenFileName("d:/exampleGIF3.gif",&error);

    error=DGifSlurp(gif);

    unsigned int  h=gif->SHeight;
    unsigned int w=gif->SWidth;

    int i,j;
    unsigned char * d=malloc(w*h*4);
    unsigned char * save=d;

    for(i=0;i<gif->ImageCount;i++)
    {
        d=save;
        SavedImage * p=&gif->SavedImages[i];

        for(j=0;j<w*h;j++)
        {
            int c=p->RasterBits[j];
            if(c==gif->SBackGroundColor)
            {
                d+=4;           //use last frame colour
            }
            else
            {
                GifColorType rgb=gif->SColorMap->Colors[c];
                *d++=rgb.Blue;
                *d++=rgb.Green;
                *d++=rgb.Red;
                *d++=0xff;
            }
        }
        char outname[512];
        sprintf(outname,"d:/image%02d.tga",i);

        SAVETGA(outname,save,w,h,4);
    }
    free(save);
    error=DGifCloseFile(gif, &error);       
}

It crashes with a memory exception while reading the third frame of 13 in this example gif

What code should I be using to get the RGB data from the SavedImage structure please ?

Thanks

Shaun

score 0 · Answer 1 · answered Jun 19 '19 at 13:13

0

Ah. The SavedImage structure has top left width and height values, hence I was reading too much data, hence the memory exception. Otherwise the code seems to work, at least with the gifs I have.

answered Jun 19 '19 at 13:13

user3162134

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How do I get the RGB colour data from a GIFLIB SavedImage structure

1 Answers1