Export to PDF & minimising the compression / resizing of images

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I'm exporting a file to PDF, containing a number of uncompressed CMKY TIFFs totaling about 630MB.

'Image Compression Method' is set to None (and, just in case, 'Image Compression Quality' is set to Maximum), while 'Limit Maximum Image Resolution' is unchecked - so I was expecting that the total PDF size would be somewhat in excess of 630MB.

In practice, the PDF generated is around 97MB, varying a little depending on whether PDF/X-1a or PDF/X-3 is used. This is significantly smaller than I was expecting, and also smaller than uncompressed PNG versions of the images (which total around 150MB).

Would I therefore be correct in thinking that it is not possible to export a PDF using either of these standards with native image quality and resolution? Or have I missed (or misunderstood) something?

Any insights would be welcome.


Images in a PDF can (from what I can see) only be compressed by two methods: JPEG and FLATE.


That means a TIFF can never be embedded "as is" in a PDF.