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I have several Illustrator files that have multiple embedded bitmap images. Some are photos and some are detailed line art.

When exporting to PDF, it is possible to control downsampling and compression for images, but the settings apply to all embedded images equally.

How can I compress only the photos as JPEG and leave the line art images untouched (or compress them less)? Can compression and downsampling be controlled separately, image by image?

The line art images contain some colour (red, black and grey lines), thus I cannot just convert them to monochrome (or even grayscale) and disable downsampling for these specific images types in the PDF export settings.

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  • I would actually trace any line art if it's all in Illustrator. The vector tracing will be much, much smaller in terms of kilobytes. Then you could merely alter compression for the remaining raster images. – Scott Mar 6 '19 at 16:01
  • @Scott Tracing them is not an option. It's complicated technical drawings ... They're fine as bitmaps and not huge (they compress very well e.g. as PNG due to the flat colours / white background). What I want is to compress all the other images (photos) while leaving these alone. – Szabolcs Mar 6 '19 at 19:25
  • The use of ZIP compression would reduce the file size without altering the quality of images – spike_66 Mar 7 '19 at 8:08
  • @spike_66 ZIP compression is much less efficient than JPEG on photos. Using only that will keep the PDF too large. – Szabolcs Mar 7 '19 at 13:06
  • @Scott Maybe one solution is to not embed the bitmap images into the Illustrator file, just link them. Then compress the separate files as needed (JPEG/PNG/etc.) Unfortunately, currently I have all of them embedded. If there a quick automatic way to convert embedded ones into linked files? – Szabolcs Mar 7 '19 at 13:07

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