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Export as PNG - Image file size

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I'm currently producing many screenshots for an online software manual and export them as PNGs. In the Affinity Photo PNG export settings I've selected what I thing produces the smallest files. However, compared to using the IrfanView image viewer for for producing these PNGs, the Affinity Photo PNGs usually have at least twice the file size. Is that eventually due to a different compression algorithm?

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Possibly you're having Photo embed the ICC Profile and Metadata (see the More... dialog while exporting) and IrfanView isn't doing that?

If you can provide an example of the same image exported from each application we can perhaps examine them to see what the differences are.


-- Walt

Windows 10 Home, version 1903 (18362.145), 16GB memory, Intel Core i7-6700K @ 4.00Gz, GeForce GTX 970
Affinity Photo 1.7.1.404 and 1.7.1.404 Beta   / Affinity Designer 1.7.1.404 and 1.7.1.404 Beta  / Affinity Publisher 1.7.1.404

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Hi,
Even if I uncheck the ICC profile, the meta data and 'Palettized', in Affinity Photo (just updated to the latest version), the attached png file produced with IrfanView takes approximately 20 kb of disk space while the same image exported with Affinity Photo takes 50 kb. I have no clue why there is such a big difference.

Affinity-VM-Review-and-Rating-List.png

IrfanView-VM-Review-and-Rating-List.png

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The Irfanview png shows as an "8-bit colormap" or "8-bit palette" file, depending on the program I use to examine them (either the file or pngcheck commands). The one from Affinity shows as "8-bit RGBA" or "32-bit RGB+Alpha".

That means you haven't saved them in truly the same format. In Affinity you would need to use the PNG-8 preset, which would give you a palettized file, rather than the PNG-24 preset. Or, using PNG-24, you would have to enable the palettized option.


-- Walt

Windows 10 Home, version 1903 (18362.145), 16GB memory, Intel Core i7-6700K @ 4.00Gz, GeForce GTX 970
Affinity Photo 1.7.1.404 and 1.7.1.404 Beta   / Affinity Designer 1.7.1.404 and 1.7.1.404 Beta  / Affinity Publisher 1.7.1.404

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The strange thing here is that my Affinity Photo (latest Windows version) produces even larger files when I select the PNG-8 preset. See next screenshot.

VM-Review-and-Rating-Edit-PNG-8.png

Update:
If I choose RGB-16 bit instead if RGB-8 bit in 'Export settings' > 'Pixel Format', the file size shrinks to 21 kb. Maybe I misunderstand something, but shouldn't that be the other way round?

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Strange indeed.

Also: I see that 1.7 has changed the PNG export settings, making some of what I said earlier incorrect or meaningless now. I'm not sure what's going on, especially with respect to RGB-16 giving you a smaller file.


-- Walt

Windows 10 Home, version 1903 (18362.145), 16GB memory, Intel Core i7-6700K @ 4.00Gz, GeForce GTX 970
Affinity Photo 1.7.1.404 and 1.7.1.404 Beta   / Affinity Designer 1.7.1.404 and 1.7.1.404 Beta  / Affinity Publisher 1.7.1.404

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