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0.92: Downscaling with gamma correction posterizes dark areas
Posted: Tue Oct 09, 2018 5:39 pm
by Daniel710
XnView: MP 0.92 - 64 bit
OS: Linux
Downscaling an image with gamma correction posterizes dark areas. See the attached image (50% size of
the original).
To reproduce, downscale an image with "Use gamma correction" enabled.
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Sun Oct 14, 2018 11:15 am
by xnview
The original have posterized area
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Mon Oct 15, 2018 9:53 am
by Daniel710
The posterized image you see in my post is the downscaled version of the original. I don't see any artifacts on the original image:
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Sun Sep 25, 2022 1:55 am
by Daniel710
Still reproducible in XnView: MP 1.3 (and also in XnResize, btw).
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Mon Sep 26, 2022 2:39 pm
by xnview
i can't reproduce with your sample image, which output size do you use? could you post the output?
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Mon Sep 26, 2022 3:00 pm
by Daniel710
Try downscale to e.g. 1806x961 pixels. You can see the output image in the first post:
download/file.php?id=5149&mode=view
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Mon Sep 26, 2022 3:59 pm
by xnview
where do you see "posterized area"?
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Mon Sep 26, 2022 4:14 pm
by Daniel710
On the Saturn rings. I attached an image with side-by-side comparison.
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Tue Sep 27, 2022 1:51 pm
by xnview
yes a known issue on dark color
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Thu Aug 29, 2024 11:25 am
by damian101
Internal bit depth needs to be higher, then this won't happen. Currently, it seems to be 8 bits per channel, which is a joke, awful banding everywhere in dark gradients. Linear light needs to be processed at 16 bits per channel (sufficient for this) or higher internally.
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Sun Aug 24, 2025 1:16 am
by Rotareneg
Just ran into this issue and was wondering what on earth was going wrong until I tried turning gamma correction off.
Top image is original, bottom is resized to 1919x1079, nearest neighbor with gamma correction enabled:
- RGB_gradient.png (9.08 KiB) Viewed 1155 times
- RGB_gradient_gamma_correct_scaled.png (8.92 KiB) Viewed 1155 times
Re: 0.92: Downscaling with gamma correction posterizes dark areas
Posted: Mon Aug 25, 2025 7:10 am
by xnview
