Preflight - Compressing only JPEG

[Jean-Claude Tremblay]

I have a PDF document that I want to compress only the image with an «image attribute : filters = JPEG« and not touching the «image attribute : filters = zlib/deflate». The PDF come from InDesign. The resulting JPEG in the PDF come from either PSD. TIF or JPG, but the image with zlib/deflate filters are PNG file.

I tried to create a Preflight profil/fix to reduce the resolution, but even if I add an option to only do it on a specific compression filter, all the images are downsampled.

I’m lost... Can this be done using a preflight profile or else?

Thanks!

[Dov Isaacs]

At first glance, I don't see a way of parameterizing Preflight (even with the latest version from a few days ago) to compress only on the basis of what type of compression the image currently is compressed with. If you want to post a sample that you think should do this, I'll be glad to look at it for you (I have responsibility for the Preflight component within Acrobat Pro).

In terms of how PDF is exported from InDesign, whether the resultant image in a PDF file is JPEG, JPEG2000, or ZIP-compressed has nothing to do with the actual format of the image as placed into the InDesign document if you use the Automatic option when exporting. The Automatic compression option actually analyzes each image and based on the content, determines whether to use ZIP compression (typically for images containing vector-like content) or alternatively JPEG (or JPEG2000) compression (typically for photographic content).

          - Dov

[Jean-Claude Tremblay]

Hi Dov,

Thanks for replying... That was more a curiosity than a need. I’m unable this morning to create a PDF with images with different compression filters. I guest, I’ll find a way, if there is to downsample only some selected images. Maybe this is something that could be added to InDesign.