[sane-devel] [PATCH 3/3] Avoid attaching grayscale ICC profiles to rgb images, or vice-versa.

[Olaf Meeuwissen]

Hi Aaron,

I'm working on your ICC profile patches but this one made me wonder what
happens with monochrome scans, i.e. grayscale with a bit depth of one.
If that works fine, I'll push your patches with two fixes after merging
against master.

Aaron Muir Hamilton writes:

>   If the ICC profile added does not match the colour format of the
>   image, libpng will abort. This can leave the scanner motors in an
>   incorrect state and possibly cause permanent damage.
> ---
>  frontend/scanimage.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/frontend/scanimage.c b/frontend/scanimage.c
> index 0f71422c..74546763 100644
> --- a/frontend/scanimage.c
> +++ b/frontend/scanimage.c
> @@ -1208,7 +1208,27 @@ write_png_header (SANE_Frame format, int width, int height, int depth, const cha
>        icc_buffer = sanei_load_icc_profile(icc_profile, &icc_size);
>        if (icc_size > 0)
>          {
> -	  png_set_iCCP(*png_ptr, *info_ptr, basename(icc_profile), PNG_COMPRESSION_TYPE_BASE, icc_buffer, icc_size);
> +	  /* libpng will abort if the profile and image colour spaces do not match*/
> +	  /* The data colour space field is at bytes 16 to 20 in an ICC profile */
> +	  /* see: ICC.1:2010 § 7.2.6 */
> +	  int is_gray_profile = strncmp(icc_buffer + 16, "GRAY", 4) == 0;
> +	  int is_rgb_profile = strncmp(icc_buffer + 16, "RGB ", 4) == 0;
> +	  if ((is_gray_profile && color_type == PNG_COLOR_TYPE_GRAY) ||
> +	      (is_rgb_profile && color_type == PNG_COLOR_TYPE_RGB))
> +	    {
> +	      png_set_iCCP(*png_ptr, *info_ptr, basename(icc_profile), PNG_COMPRESSION_TYPE_BASE, icc_buffer, icc_size);
> +	    }
> +	  else
> +	    {
> +	      if (is_gray_profile)
> +	        {
> +		  fprintf(stderr, "Ignoring 'GRAY' space ICC profile because the image is RGB.\n");
> +	        }
> +	      if (is_rgb_profile)
> +	        {
> +		  fprintf(stderr, "Ignoring 'RGB ' space ICC profile because the image is Grayscale.\n");
> +		}
> +	    }
>  	  free(icc_buffer);
>  	}
>      }
> --
> 2.12.2

--
Olaf Meeuwissen, LPIC-2            FSF Associate Member since 2004-01-27
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