The threshold filter produces inconsistent and incorrect results for me when threading is enabled and the filter is used with an image having a color depth greater than 8 bits.
Typically, the issue shows up as pixels which don't correspond to the source image (e.g. a black pixel from a light pixel in the source, even at a low threshold), or rectangular blocks that are either solid black or have a color which is not black or white. The result will be different each time the filter runs.
It can be reproduced with the following steps:
- Create or open an image with a color depth greater than 8 bits
- Use threshold filter
- Toggle preview (toggling multiple times may be needed)