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index color

Forum|Forum|7 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

Legend

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

Community 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

Legend

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

Community 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.

rob day

Community Expert

Dov,

I don't think we're really disagreeing. We're just looking at the situation from two different perspectives. As a teacher who teaches a lot of future designers at UC Berkeley Extension and other venues, I notice that students these days are a lot more familiar with working with preparing art for the web and devices. It's really important to teach them about issues like print resolution, RGB vs. CMYK colors, stuff like that if they're going to design for print. That's why I put the emphasis on not choosing a file format which could potentially reduce colors through ignorance.

For the information of the OP and others reading this, here's another way of detecting Indexed Color. I mentioned that Bridge reveals it if you select the image. But you can also see it in a PDF file after Indexed Color image has been placed in the file. You need to use the Print Production Tools in Acrobat Pro. Open Acrobat Pro and use the Search field under Tools to open Print Production Tools. Select Output Preview at the top right.

In the Output Preview panel, select from the Preview menu toward the bottom and select the Object Inspector. Move your cursor over a picture (or any other object) and you'll see an analysis of what is under the cursor, in this case the attributes of the image—including ColorSpace: Indexed DeviceRGB. (My cursor was over the lower image.)

If preflight caught indexed RGB you might wonder what the user would do? Converting your example to 24-bit wouldn’t have any affect on output—the obvious posterization artifacts would still print.

Some kinds of continuous tone images could be rendered adequately with 256 colors—i.e., a monotone image—if the index color compression (limited colors) is a problem you should be able to see the artifacts in the PDF. It’s similar to the JPEG format, where compression artifacts may or may not show in print, and it would be difficult for a preflight rule to pick up on that threshold.

T

Test Screen Name

Legend

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

Steve Werner

Community Expert

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

Jeff Witchel, ACI

Community 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

Community 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

Community Expert

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

S

SJRiegel

Legend

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

Community 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

Community Expert

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

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