I preface this post by saying this isn't an issue with the PSX core, rather I think an issue with the PAL version of the game. I thought I would ask this question here in the hope of finding someone knowledgeable on the subject of PSX dithering that may know what is going on.
With an emulated version of Syphon Filter 3 releasing on PS5 this week I was comparing the NTSC and PAL versions of the game to see how they differ. I noticed that the PAL version of the game had a visually very "noisy" image compared with the NTSC version. I initially thought perhaps this was an issue with Sony's emulator, but I compared with the PAL version running on Mister (and other emulators) and found the same defect.
I've tried to capture this from the Mister to demonstrate what I'm seeing - which you can see here - it seems that the dither pattern on the PAL version is very jumpy / glitchy / wobbly compared with the NTSC version which is static. This was captured with the stock settings on the PSX core.
Obviously I can disable dithering and enable 24bit rendering (or just play the NTSC version) and the issue goes away, but I'm curious as to what the actual issue is. Are there any other examples of PAL games having this problem with dithering?
Testing further with DuckStation I noticed you could mitigate the issue by using it's scaled dithering option (which "scales the dithering pattern to the resolution scale of the emulated GPU") - which makes me wonder if this is just another example of an issue introduced during the NTSC to PAL porting process (eg. they included the "wrong" dither pattern for the resolution which the PAL version would run at).