Overexposed pixels turning purple/magenta

[ddv2005]

Issue: Overexposed pixels turning purple/magenta. Overexposed pixels have to be detected and recovered (highlight recovery/highlight desaturation) before applying CCM but PISP missing this step and clipped pixels turning purple after applying CCM. There are no way to avoid overexposed pixels on bright light sources (like sun) if we need shadows. But they have to be properly handled.

https://forums.raspberrypi.com/viewtopic.php?p=2376866#p2376866

Hardware & OS Specifications:

• Board: Raspberry Pi 5, CM5
• Camera: Official Raspberry Pi Camera Module V2 (Sony IMX219), Arducam IMX462
• Kernel: Linux thv2 6.18.29+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.18.29-1+rpt1 (2026-05-12) aarch64 GNU/Linux
• OS: Debian 13 (Trixie) and Debian 12 (Bookworm)
• libcamera versions: 0.7.1 on trixie and 0.5.2 on bookworm

Test images (jpeg & raw): test_images.zip

[davidplowman]

Hi, can you say how you captured the images? It would be helpful to see some metadata at the time of the capture.

If you used Picamera2 with (for example) request = picam2.capture_request() then the metadata would be in request->get_metadata(). If you used rpicam-still then you should be able to add the parameters --info-text "%exp %ag %dg %rg %bg" to see the exposure time and all the gains on the window title.

Thanks.

[ddv2005]

It was captured via rpicam-still with --raw option. Unfortunately --info-text does not work with DRM/KMS output.
I made changes in my app to print gains & ccm and found that the problem appears if Digital Gain less than 1.0f
20:40:06.935 [2201] [1] WB 1.536089 1.975485, dg: 0.167986, ag: 1.000000
20:40:06.935 [2201] [1] CCM:
1.9417 -0.6720 -0.2697
-0.6161 2.2221 -0.6060
-0.0492 -0.9908 2.0399

I am testing by flash light because of no sun during a night :-) . With Ae enabled I have purple circle in the center (with dark background) and the lower digital gain the more saturated purple. If I disable Ae then image almost white with very light purple circle but the whole image is overexposed but just a circle.

[ddv2005]

I guess that a8b4220 will fix a problem by keeping colors clipped to max. The only thing that instead of clipping Digital Gain to 1.0 it may be good idea to fix void IpaPiSP::applyWBG to apply Digital Gain first and then calculate extraGain to make sure that gains >1.

[davidplowman]

Hi, thanks for the update. Yes, I think the smoking gun here is the digital gain value which has become less than 1, and this will be fixed by that commit. You could either wait for the fix, or build libcamera for yourself if you wanted to try it earlier. We can always revisit the problem after that. Thanks.