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I've wrote a program that uses iTextSharp to produce PDF files. I'm currently producing PDF files used solely for print (personnal and professional) that contain CMYK images.

The source images are RGB pictures.

The way I do it is to convert the RGB pictures to CMYK tiff images using Image Magick and two color profiles (sRGB.icc for the source, and USWebCoatedSWOP.icc for the target CMYK).

This results in big tiff files (a 26 KB jpeg file for instance becomes a 1 MB tiff) leading in turn to a huge PDF file.

I've done a bit of research in order to make the files smaller. I've read answers to a related question (Which file format is best for printing?) but I don't know if I'm doing it right, or if there's a better approach.

1) Is there a better format than tiff for storing CMYK in PDF files? Apparently EPS doesn't work well on all printers (see link above). I can't find a single JPEG2000 CMYK image to test, nor do I know if it's supported by PDF files (or the coming PDF2 files). JPEG CMYK work also, but are bigger than tiff files for my set of images.

2) Should I rather include the RGB files and embed the ICC profile in the PDF file? Does it work? Does it lead to the same result?

3) Any other ideas?

Thanks

  • If they are for printing, the best format is lossless, 1:1 pixel size @300 dpi (i.e. 1 inch printed square would have an image 300px x 300px). 300 x 300 x 4 channels is 360,000 bytes or 350KB, uncompressed. Big file sizes are just part of the business, and any optimization is really just another word for quality reduction. – Yorik Jul 21 '16 at 15:49
  • Another thing to keep in mind so you don't drive yourself crazy is that on the prepress side Rips have gotten so good that you can have a mix of RGB and CMYK and it handles them just fine. Now if you are looking to match up color "exactly" without any sort of color shifts then it's best to work with your printer and get a set of color profiles from them. That is a whole other discussion and can drive you to drink. As far as file formats for CMYK, I usually just use .PSD or .TIF files. Most of my layout occurs within InDesign so you can import most anything. – ErickP Jul 21 '16 at 16:33
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Sounds like you're doing it right to me.

1) Tiff files are pretty much standard, as far as print-ready PDFs go. In my experience, anyway. They are an uncompressed image format, so you will always have a large file size.

2) If you are printing in CMYK, to play it safe, your artwork should all be CMYK as well. Otherwise, you might end up with undesired results when printing the final product and wonder why colors aren't exactly the same.

Working with full-resolution, high-quality images for print will always have the added consequence of large file sizes.

Like Yorik said, sacrificing file size is also sacrificing quality.

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    Actually, TIFF data within the container can be uncompressed, or LZW ("zip"), or JPEG. Possibly others (or any), but the opening software may not support anything beyond those 3. I usually opt for LZW, since it does reduce size without loss. – Yorik Jul 21 '16 at 17:29
  • @Yorik Good point. I always forget about the compression, since I always work uncompressed. – Manly Jul 22 '16 at 16:57
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I think I tried everything so here are my recommandations:

  • use ZIP as the compression format, rather than LZW
  • merge all layers in one layer
  • think about stripping the metadata from the file and put the color profile in the PDF file instead (with PdfWriter.SetOutputIntents). This saves a lot of bytes when you have multiple images using the same color profile.

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