On behalf of Adobe,
There is absolutely nothing wrong with indexed color. All indexed means, as explained earlier in this thread, is that the image in question has no more than 256 distinct colors used. And contrary to popular belief, indexed color may be either RGB or CMYK. Indexed color is simply a method by which a single byte table lookup value could be used to express an RGB or CMYK value as opposed to either three bytes (RGB) or four bytes (CMYK).
There are many images that in fact use no more than 256 distinct colors, especially when dealing with screen shots or images that possibly were derived from simple vector diagrams.
In terms of how images with indexed color work, they are processed no differently than images that are not indexed. When creating PDF files, Adobe applications will automatically use indexed color if no more than 256 distinct colors are found in the image. You have no control over that! And there is nothing wrong with this! All Adobe (and competing products that we know of) handle images with indexed color without any issues whatsoever.
Thus, if you have a printer that you “need to fix” content that ends up as indexed color, you are dealing with a printer that either (1) is concerned that you may be using low quality artwork (i.e., relatively few distinct colors) or (2) simply doesn't know what they are talking about. We know of no RIP/DFE and/or PDF workflow component that doesn't properly deal with images with indexed color.
Feel free to point such “printers” to me if they still give you issues over this.
- Dov
- Dov Isaacs, former Adobe Principal Scientist (April 30, 1990 - May 30, 2021)
