Re: [GD-DEVEL] bug in gdImageGetPixel & JPEG Images? (OS X)

Hi Ian,

On 6/24/07, Ian Banfield <[email protected]> wrote:
> Hello!
>
> I'm using OS X 10.4.10, xCode 2.5 (which uses gcc to compile C), GD
> 2.034 and libjpeg, installed via macports. (The same problems occures
> if everything is compiled from sources, including 2.035 and the
> latest CVS snapshot). The linker flags are set to "-lgd -lpng -lz -
> ljpeg -lfreetype -lm", library search paths to /opt/local/lib and
> header search paths to /opt/local/include (which should be the
> appropriate settings for GD if it was installed via macports).
>
> My code basically consists of the gdImageGetPixel example in the manual:
>
> #include <stdio.h>
> #include "gd.h"
>
> int
> main (void)
> {
>         FILE *in;
>         gdImagePtr im;
>         int c;
>         in = fopen("image.jpg", "rb");
>         im = gdImageCreateFromJpeg(in);
>         fclose(in);
>         printf("%d by %d\n", gdImageSX(im), gdImageSY(im));
>         c = gdImageGetPixel(im, gdImageSX(im) / 2, gdImageSY(im) / 2);
>         printf("The value of the center pixel is %d; RGB values are %d,%d,%d
> \n", c, im->red[c], im->green[c], im->blue[c]);

That's the problem. You are accessing the palette directly. It is not
recommended (and may not be supported in future version.

> This works very well for gif files (replacing image.jpg by image.gif
> and ..createfromJpeg by ..fromGif)

Loading a GIF image create a palette based image. The red/green/blue
element are filled using the GIF palette. JPEG always creates a
truecolor image. The palette elements are not used.

I suggest to use the gdImageRed, gdImageGreen, gdImageBlue macros if
you do not know if the image is true color or palette.

> Any ideas?

I hope it helps you to fix this problem :)

Cheers,
--Pierre