RGB/16 to RGB/8 conversion issues

[NotMyFault]

Hi,

when I try to convert the document from RGB/16 to RGB/8, black spots will be created in the right-middle area.

 

Best observable when using Chanels panel and choosing only one color channel. The images show green channel.

Image 1: RGB/16 (looks ok)

Image 2: RGB/8 (black pixels are wrong)

Image 3: Conversion

alpha channel packing.afphoto

[NotMyFault]

The issue is probably caused by the alpha channel which is almost zero in that area. the loss of the lower 8 bit causes an unexpected effect.

I would expect that the color channels and alpha get converted individually. It seems that the least significant bit get rounded randomly to 0 or 1, so the color channels get erased where alpha gets zero. 

The "all 8 bit colors" was generated with help of PT filters (so no dithering has happened there), then I added a rectangle with conical gradient on alpha (which may create the unwanted dithering, even if color is pure white at all nodes).

[Callum]

Hi NotMyFault,

I have logged this with our developers to be investigated further I'll update this thread once I have more info.

Thanks
C

[NotMyFault]

I repeated the test, using a PT filter to create a linear gradient, and rectangle to polar filter. The only difference to a regular fill ist that no forced dithering gets applied. Using that layer no black dots occur.

So the issue is created by forced dithering applied even to alpha channel when using gradients.

Can be closed, i will bump the feature requests to get rid of forced dithering.