[sf-lug] Forcing a greyscape JPEG into RGB colorspace?

jim jim at well.com
Mon Jun 14 11:02:36 PDT 2010

   my initial reaction was "what?" i.e. how to 
infer hue from greys. 
   after some more coffee it occurs that maybe 
you want an RGB representation of greys, yes? 
i.e. Ox777 would be mid-grey, 0xFFF white, 
0x000 black, etc., yes? 

On Mon, 2010-06-14 at 10:30 -0700, Bill Kendrick wrote:
> So I've got a system that receives images from users
> We then ship those out to a 3rd party.  This 3rd party
> requires that they be JPEGs (easy to convert to) of a
> certain size (easy to check) and in RGB colorspace
> (vs CMYK or Grey).
> I had a great bit of difficulty, and simply threw my hands up,
> when trying to "encourage" a greyscale image (that is, a picture
> that's only grey pixels) to become an RGB colorspace JPEG.
> Every automated tool I tried (libjpeg-progs, ImageMagick,
> possibly others; it's been a while) seemed to ignore my colorspace
> hint, and said to themselves "ah, but it's only grey pixels;
> let's just save it as Grey colorspace!)
> Does anyone here have any suggestions on a tool that can handle
> this for me?  (Again, this will be running on a server as part
> of an automated process, so desktop apps are out; don't bother
> suggesting The GIMP :) )
> I'd be willing to whip something up in C that used libjpeg
> and ran on our server to handle the 'force-to-RGB-colorspace'
> task.  (The other idea I had was to introduce an off-grey pixel
> into the source image, to "convince" the tools we're using now
> that the image really does deserve RGB colorspace :) )
> Thanks in advance,
> -bill!
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