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index color

Forum|Forum|6 years ago
March 13, 2019
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I have a client that send me a project and I try to check everything, but when I sent it the printers they will tell me I have index color and I need to fix it. Is there an easy way in Indesign to check for index color without highlighting all the text or vector artwork?

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Correct answer Dov Isaacs

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

T

Test Screen Name

Brainiac

I may be speaking out of turn but I read Dov Isaac's "All Adobe (and competing products that we know of) handle images with indexed color without any issues whatsoever" as talking only about the handling of PDF files (and not their creation).

Steve Werner

Adobe Expert

We've completely left the OP in the dust. It wasn't very clear what the OP's situation was.

I interpreted the "I have a client that send me a project and I try to check everything" part as a query about how to find out if there were a way to find bad indexed files and how to prevent them.

Dov focused on the printer (since he spends a lot of time talking to dumb printers) and the fact that they only accept very limited formats based on their often ancient knowledge from 1990s printing.

Dov IsaacsCorrect answer

Brainiac

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)

Steve Werner

Adobe Expert

Dov, what you're saying is exactly right. There is nothing wrong in reproducing images which have a small number of colors using indexed color.

But some of us are looking at things from a teacher's point of view (and perhaps from some printer's point of view). Inexperienced users may not realize that choosing to save a picture which has many more colors as a 256-color GIF file will reduce quality.

It's better to tell them NOT to use GIF for printing so they won't inadvertently make the mistake.

Below is a picture which starts with many colors. When reducing the number of colors you create a similar effect as choosing an over compressed JPEG file. The top picture is 300 ppi effective resolution in RGB. The lower picture was saved as 256-color GIF Indexed Color. Look particularly at what happens to the sky area. Click on each picture to view.

Dov Isaacs

Brainiac

Steve,

There is no question that downsampling the number of colors in an image simply to make it a GIF file is ludicrous, at best.

And I would agree that in an educational environment, advocating not saving an image as GIF since by definition it will discard color data is quite appropriate.

But to extend that to banning use of indexed color in PDF is absolutely wrong. Nothing is to be gained by somehow forcing what is inherently an image with no more than 256 distinct colors to not be indexed. And unfortunately, broad generalizations about not using indexed color encoding end up being taken as gospel by those who simply can't or are unable to grasp the technical underpinnings. This is not too different from other prepress crazinesses such as forced outlining of text, not allowing images less than 300dpi, etc.

Note that the OP in this thread said absolutely nothing about the original images being GIF. Indexed color could have been created by InDesign during PDF export for any image in which there were naturally no more than 256 colors.

- Dov

- Dov Isaacs, former Adobe Principal Scientist (April 30, 1990 - May 30, 2021)

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Test Screen Name

Brainiac

This is a non-problem. Indexed colour is not a problem unless someone, who doesn't understand what it is, rejects it.

Steve Werner

Adobe Expert

An indexed color GIF would be a very poor choice for a printing job, being limited to 256 colors.

Jeff Witchel, ACI

Adobe Expert

You could set up a Preflight Profile to check for color and other issues in your document. Here's a video about it: http://www.jeffwitchel.net/2012/08/finding-potential-printing-problems-automatically/

Or, even better, ask your printer for their Preflight Profile. You can load their Profile to your Preflight Profiles (see about 1:25 into my video).

Hope this helps!

Steve Werner

Adobe Expert

But Jeff if you look at the dialog box in SJSiegel's posting, Indexed color is just RGB. It doesn't have a separate listing. That's why she suggested a feature request. I thought it had a separate checkbox but it does not.

Jeff Witchel, ACI

Adobe Expert

You're right Steve! That would make a good addition to Preflight.

S

SJRiegel

Adobe Expert

You can add Color Space as a Column in your Links Panels, and then sort by color space to see all of the items that use Indexed RGB.

A preflight profile would be preferable, but Indexed RGB is not listed separately in Color Space and Modes Not Allowed.

(This might be a feature request if you encounter it often)

Steve Werner

Adobe Expert

Indexed color would occur in an image file and not in text or vector artwork. It's an RGB file which has been saved so it's limited to 256 colors, rather than millions of colors. Likely it's a GIF file, so when you see an image with that extension, you could view it in Bridge where you it will tell you that it's indexed in the Metadata panel:

Derek Cross

Adobe Expert

Presumably the image is a GIF, you can change the color mode in Photoshop: Image > Mode > RGB.

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