Picamera with custom lens, color issue

[zbarna]

Hi!

We are using the Raspberry Pi3 B+ model with the picamera V2.
We changed the original lens to an other simple lens, because it was necessary for our project.

Unfortunately with the new lens the colors in the middle of the picture is fine, but on the sides it's pink or magenta.

Original Lens:


Custom Lens:


In the second picture you can see on right side it should be yellow like in the middle, not pink or magenta.

Could you recommend us something how to solve this issue? Should we use a filter in the lens, or need to modify the camera settings on the raspberry?

Thanks for your help in advance!

Best Regards,
Zoltán

[PiGraham]

Corrections are applied for the standard lens. The issues are discussed here:
viewtopic.php?t=168777

You can get the raw pixel values and apply your own Bayer processing and colour corrections for still images.

[6by9]

You can override the lens shading tables - viewtopic.php?p=1199174

[zbarna]

Thanks for the info, I will check the forums you linked!

[zbarna]

Hi!

We disassemblied the picamera sensor, and found that, maybe there is an issue with the sensor itself. If you check the picture, I've taken about the sensor, you can see a dark circle in the middle of it:


The other strange thing is that, if we use the picamera without lens (so only the sensor), this circle color issue also exists on the pictures.
What do you think about this?

One more question: If I override the color shading table, it will also has an effect on the picamera preview or only on the captured pictures?

Thanks for your answer in advance!
Best Regards,
Zoltán

[6by9]

Sorry, you aren't going to get much support when you have so completely stripped down the sensor.
The sensor and lens assembly are designed to work together. In particular there will be some compensation within the micro-lens array to adjust for the chief ray angle and lens vignetting. That is a likely reason for the odd colour effects you are seeing when looking at the sensor.

One more question: If I override the color shading table, it will also has an effect on the picamera preview or only on the captured pictures?

Yes, it applies to all images produced via the ISP.

[PiGraham]

The other strange thing is that, if we use the picamera without lens (so only the sensor), this circle color issue also exists on the pictures.
What do you think about this?

I think that is to be expected. The lens introduces a circular shading pattern. The correction for that will be an inverse circular pattern. If you illuminate the sensor with very even illumination you will see the circular inverse pattern. The only situations were you won't see that pattern is either if you use a lanes and matched correction (e.g. the stock lens the correction is designed to cancel out) or if you disable shading correction entirely and illuminate the sensor uniformly.

[zbarna]

Hi!

Thanks for the explanation for both of you!