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October 2006
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2006.10.16 21:47 "Re: Tag 346", by Ross Presser
Joris, > Ross Presser wrote: > > Is there any extant software anywhere that implements this, either for > > writing or reading? (I have some hints that Pagemaker supported it at > > some point.) > > > > Also, are there any sample images anywhere? > > To the best of my knowledge, that's a 'no' on both questions. I've never > seen any file come my way that uses the Indexed tag. I can write it with > my proprietary codec, but I'm careful to not let those experimental > files escape into the wild and would not want to ship a version of my > codec that writes them to anyone. > > I believe the design of the 'Indexed' tag is not without serious flaws. > For one thing, it changes the meaning of the other most crucial tags. [snippage] Thanks for that information. It certainly makes sense then; the tag was proposed without having been fully thought out, so it never got used. The reason I asked is slightly off topic for TIFF, in fact. As you probably know, the PDF spec does support Indexed images in any colorspace defined in the PDF. In fact, the default profile for Adobe Distiller will automatically convert *all* images in the source to indexed images as long as the total color count is less than 256. This can yield some terrific compression: the files in my workflow each contain a single 8636x9144 pixel bitmap that uses only three colors -- black, white, and 100% magenta; the file sizes range from under a megabyte to about three megabytes. It's perfect for this application. But since there are apparently *zero* raster file formats that can contain indexed CMYK images, it's impractical to do any image manipulation on these bitmaps. Extracting them as full CMYK TIFFs swells them to 100-315 mb. I am considering writing a custom tool that converts them to RGB palette on the fly, and back again. Since the colormap is so simple, I can hardcode it into the tool and not worry about losing any color information in either direction. Thanks for your time. I'll give up on the idea of using tag 346 then.