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Image size and exported PDF size


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I am typesetting a book in Affinity Publisher. The author provided me with photos that will go in the book. These were scanned at very high resolution (I believe 4800 dpi and 48-bit color) from her slides as TIFFs, with very large file sizes.

In Affinity Photo I resized them by changing the dpi to 300 (standard for printing) and then setting the horizontal size at 1900 pixels, with the vertical size calculated automatically. If my math is correct, 1900 pixels is the right size to fit properly across the page as I have designed it.  Then I exported the photos as PNG‘s.

The problem is that the PNG files are still very large, about 12 or 13 MB. If I put 40 of these into the book, the final PDF will be over the limit that the printer will accept. What is the best way in Affinity Photo to reduce the size further while maintaining the quality?  Or is there some way in Publisher to shrink the photos (again, maintaining the quality) when I export the final PDF? (The images are linked, not embedded, in Publisher.) I know that there is an option when exporting PDFs to reduce images that are over a certain resolution, but since I’ve already changed the photos to 300 dpi I don’t think that will address the issue.

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8 hours ago, DJP said:

PNG files are still very large, about 12 or 13 MB. If I put 40 of these into the book, the final PDF will be over the limit that the printer will accept.

You cant calculate with the PNG file sizes for the exported PDF. Not only Affinity PNG are relatively large (compared with other software) but also the JPG compression you can use for PDF export may result in a quite different file size.

Generally there is no need to resize the images before using them in APub, instead the downscaling and recompressing happens on export ( … unless you would deactivate any resampling & recompression in the export settings).

You have three choices to influence the output file size:

• If you don't tick the checkbox "Convert image colour spaces" the RGB images will be maintained in RGB and get their profile added for correct CMYK conversion in the printers pre-press process. This will result in about 20-25% smaller PDF file size compared to have all images converted to CMYK. – Check the expected / required profile and PDF version with your print service.

• Reducing the export resolution will reduce the output file size. Though 300 dpi are standard, depending on the image content also less may give sufficient results, e.g. 280 or 250 dpi. A test will show you the difference, for visual comparison on screen view the results at about 250 – 350 % (because a screen doesn't display with 300 dpi like print but rather about 72 – 144)

• Also reducing the export JPG compression quality leads to smaller file size. The most file size effect happens between 100 and 85 % quality, below the effect gets smaller and possible compression artefacts may get visible, again depending on the image content. An export with 100 – 95 % compression quality results in an obviously larger PDF than 85 %.

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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5 hours ago, lacerto said:

Obviously compression of 48-bit images is less effective.

Your 48 bit file sizes remind me of an issue reported in earlier* APub versions, where it appeared that images above 24 bit did not get compressed on PDF export. Also I vaguely remember that Affinity PDF export in macOS in certain circumstances can use another compression than JPG, ZIP or LZW which is not listed in the export options. – Have you read what compression was used in your larger PDF files?

*compare…:

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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On 11/1/2022 at 12:38 AM, thomaso said:

• Also reducing the export JPG compression quality leads to smaller file size.

Thank you for the very helpful reply.  I'm using PNGs not JPGs, so I assume the compression you mention won't apply in my case (unless Publisher converts everything to JPG on export??).  The photos use the color profile that is specific to the Epson V850 scanner with which they were digitized--this gives noticeably better color than Epson RGB or sRGB.  I set the Publisher document to CYMK since that is what the printer prefers, although he can accept sRGB.  I'm not quite sure how all this fits together.  I assume that Publisher can convert the Epson-specific profile to CYMK properly when I generate the PDF for the printer.

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On 11/1/2022 at 10:45 AM, lacerto said:

. . . you can typically get file sizes that are about a quarter of the sizes (both PNG and final PDF) if you save the images as 24-bit (8 bits per channel). You do not gain anything in quality by printing with 48-bit images.

Very useful info, thanks!  In Affinity Photo, if I choose Document>Convert Format>RGB8, that is 24-bit (since 8 x 3 channels = 24).

On 11/1/2022 at 10:45 AM, lacerto said:

I would convert the original images to 24-bit RGB (PNG or TIFF), place them in the layout and export using any of the method (e.g. Press Ready 1.7, PDF/X-3 or PDF/X-4) that keeps the images as RGB images

I set up the Publisher document as CYMK because that is what the printer prefers, but he will accept sRGB also.  Should I change the whole document to RGB/8, or do the photos stay as RGB if I choose one of the export options you mention?

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44 minutes ago, DJP said:

I'm using PNGs not JPGs, so I assume the compression you mention won't apply in my case (unless Publisher converts everything to JPG on export??)

About the PNG compression method see the recent reply of @Lacerto (right above your last response). Also consider that PNG isn't meant to use CMYK space, which may mean if you convert them on export to CMYK (again according @Lacerto's hints) they won't be PNG anymore – which would mean it can make sense to place JPG in the layout instead of PNG.

However, initially you asked about options to reduce the exported PDF file size, so possibly it doesn't work to stick with all quality parameters like file format and compression.

Just in case: the comparison on this website gives quite a good overview for various JPG compression rates shown with different types of image content (scroll down to an image and hover over the various compression rates …). Though it was done for JPGs exported from Lightroom it still may give an idea about the size / quality ratio:

http://regex.info/blog/lightroom-goodies/jpeg-quality

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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5 hours ago, lacerto said:

choose the recommended profile. If you can do this before right from the start before having placed any images in the document, that would be good.

By the way, do you have an idea or knowledge about the use or speciality of "generic" colour icc profiles like those in macOS, "Generic CMYK", "Generic XYZ"…?

I got aware of them when my default PSO_coated_v3 or ISO v2 profiles started annoying me in a bunch of simple, small CMYK test .afpubs because of increasing the file size. Do you know if it can make sense to use such a "generic profile" as Affinity default, either for test files that don't get produced or especially as long a finally required export profile by the printer or client is known?

328163678_genericprofiles.thumb.jpg.3b238d61651fe0b68fd491b2165ee926.jpg

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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4 hours ago, lacerto said:

I have no idea what would not get translated if such generic profiles were used, but perhaps the size does matter in this context ;-).

Yes, and size was the reason to make it interesting to me ;-). I wonder if the small size would mean they do nearly nothing with colours (like NO profile ?). It appears that especially linear or wide-gamut RGB profiles have a small file size (below 1 Kb) whereas the size of CMYK profiles varies a lot (~ 0.5 kB – 3 MB).

1983510005_colourprofilesfilesize3.thumb.jpg.f91951b65a5c57a7974c232975660015.jpg

584922919_colourprofilesfilesize2.thumb.jpg.0fa43fb37569f1d6cbcce2aff10e6c35.jpg

62103999_colourprofilesfilesize1.thumb.jpg.7bc08f2c0b809b373a423a905ddfc67d.jpg

It feels odd that I am unable find any info about "Generic…icc" profiles, even the Authors of the "PDF-Bible" (600 pg., by Merz @ PDFlib / Drümmer @ Callas software) didn't mention "generic" .icc as specific profiles in their German book from 2002 – which might mean they have no use at all, and/or just that Apple did create it later. Whereas the paper supplier Canson has its own (odd) understanding of "Generic profile": https://www.canson-infinity.com/en/what-generic-icc-profile

Have you ever seen "Generic…icc" profiles in Windows, or are they some Apple speciality?

Apple mentions "generic" for colour spaces and it appears to be used as synonym for "device independent":

https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_color/dq_color.html
1237316218_colourgenericApple.jpg.e5d5c2746fe6793ddc3c0662d5433977.jpg

Their use of "specific" + "device independent" sounds confusing, to me independent wouldn't be specific and vice versa, while "leave to the system" sounds like no change / influence at all. (but this is about spaces, not profiles …?)

943787725_colourgenericApple2.jpg.414a357e8ecc58ee5aff9330b97e54c0.jpg

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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