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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
Designer, Photo, and Publisher V1 and V2 at latest retail and beta releases
PC:
    Desktop:  Windows 11 Pro, version 23H2, 64GB memory, AMD Ryzen 9 5900 12-Core @ 3.00 GHz, NVIDIA GeForce RTX 3090 

    Laptop:  Windows 11 Pro, version 23H2, 32GB memory, Intel Core i7-10750H @ 2.60GHz, Intel UHD Graphics Comet Lake GT2 and NVIDIA GeForce RTX 3070 Laptop GPU.
iPad:  iPad Pro M1, 12.9": iPadOS 17.4.1, Apple Pencil 2, Magic Keyboard 
Mac:  2023 M2 MacBook Air 15", 16GB memory, macOS Sonoma 14.4.1

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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
Designer, Photo, and Publisher V1 and V2 at latest retail and beta releases
PC:
    Desktop:  Windows 11 Pro, version 23H2, 64GB memory, AMD Ryzen 9 5900 12-Core @ 3.00 GHz, NVIDIA GeForce RTX 3090 

    Laptop:  Windows 11 Pro, version 23H2, 32GB memory, Intel Core i7-10750H @ 2.60GHz, Intel UHD Graphics Comet Lake GT2 and NVIDIA GeForce RTX 3070 Laptop GPU.
iPad:  iPad Pro M1, 12.9": iPadOS 17.4.1, Apple Pencil 2, Magic Keyboard 
Mac:  2023 M2 MacBook Air 15", 16GB memory, macOS Sonoma 14.4.1

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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
Designer, Photo, and Publisher V1 and V2 at latest retail and beta releases
PC:
    Desktop:  Windows 11 Pro, version 23H2, 64GB memory, AMD Ryzen 9 5900 12-Core @ 3.00 GHz, NVIDIA GeForce RTX 3090 

    Laptop:  Windows 11 Pro, version 23H2, 32GB memory, Intel Core i7-10750H @ 2.60GHz, Intel UHD Graphics Comet Lake GT2 and NVIDIA GeForce RTX 3070 Laptop GPU.
iPad:  iPad Pro M1, 12.9": iPadOS 17.4.1, Apple Pencil 2, Magic Keyboard 
Mac:  2023 M2 MacBook Air 15", 16GB memory, macOS Sonoma 14.4.1

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