Indexed CMYK in my Illustrator PDF files!

[Jeff_Morrison@adobeforums.com]

Can someone help / explain this. When I save my Illustrator file as a PDF I end up with tons of "indexed" CMYK elements. Why is this? If I take the same document (AI) and place in InDesign CS and export as PDF, I get zero Indexed CMYK images. I sure could use some help on this.

[Scott_Falkner@adobeforums.com]

How can you tell that images are indexed and CMYK? I didn't even know this was possible.

But...

Perhaps if you have some raster images that can be safely indexed, then Distiller is smarter than Indesign about tagging these images for indexing. Indexed images are like GIFs, in that the compression can be significant, yet lossless.

[Jeff_Morrison@adobeforums.com]

I can tell by using Pitstop on the PDF once created. I'm looking for a way to avoid this, since "indexed" causes them to fail preflight tests.

[Scott_Falkner@adobeforums.com]

"indexed" causes them to fail preflight tests.




But do they actually print fine? If so, then can you change your preflight software to ignore this? Either way, passing a preflight test is not what you are after is it? It's printing without error or complication.

[Jeff_Morrison@adobeforums.com]

Actually, I'm preparing files for printers in many locations. I have no way of knowing what RIPS these guys are using and what errors they might encounter. So, I set it to check for things that printers commonly have issue with...like indexed colors. Some printers won't even attempt to print it if it fails their preflight test. See the delimna?

[Doug_Katz@adobeforums.com]

I've never actually experienced this. What does Acrobat actually TELL you? What IS an "indexed CMYK element"?

[Jeff_Morrison@adobeforums.com]

I really don't know. Illustrator doesn't tell me anything, this information is coming from Pitstop when I inspect the PDF file. Illustrator created the PDF. According to Pitstop documentation, CMYK can be "Indexed" just like RGB can be. What does this mean in the end...I have no idea. All I know is Illustrator produces this while InDesign does not.

[jonf@adobeforums.com]

GIF=lossless? That's news to me. How can a GIF of any half-tone image be lossless?

It seems that any indexing has to strip out some level of middle values from halftone gradations, or it hasn't actually indexed the colors. An image of flat colors can be severely indexed with no loss. But a photo?

Maybe I learned this all wrong. It wouldn't be the first time.

Could it be that you're saving your pdfs out of Illustrator with some other compression mode than "jpeg" which may be indexing the color?

[Scott_Falkner@adobeforums.com]

It seems that any indexing has to strip out some level of middle values
from halftone gradations, or it hasn't actually indexed the colors. An
image of flat colors can be severely indexed with no loss. But a photo?




Posterization or Aliasing plus indexing will caouse loss of data. Indexing alone will not. Imagin a grayscale image that has no gray values in it, just black or white. Indexing will reduce the size of this image significatly, sinceone byte can now do the work of four, but won't effect the image quality at all.

If a photo is being indexed, then I guess something is wrong there.

Either way, I have long understood that Distiller is THE way to produce PDFs for prepress.

[jonf@adobeforums.com]

But a photo has gray values in it...pretty much every value of gray between black and white. Unless it's been halftoned already into a b/w dot screen. I don't suppose his image was already halftoned before he made the pdf? That might allow it to index, but I still don't see what caused it to index.