- Edited
We already know how to determine the presence of spatial dithering by reading the state of the Intel iGPU/GPU controller register. But I became curious whether it is possible to visually see the presence of spatial dithering on Intel graphics cards. And at the same time, check if it is possible to enable temporal dithering. There will be nothing new in this post, only a visual confirmation of the facts we have known for a long time.
The test was conducted on Windows 10 22H2 using an Intel ASRock ARC A770. To enable or disable dithering, the application ditherig was used.
Screenshots were taken using a Blackmagic UltraStudio Recorder 3G. Since it doesn't always work correctly with the HDMI port on the ARC GPU, I connected it via DP.
Link to the archive with screenshots and resulting comparison files.
The comparison was performed using this python script.
The archive contains pairs of screenshots with dithering (spatial dithering) enabled and completely disabled, as well as the result of their pixel-by-pixel comparison. There is one unpaired screenshot, without_ditherig_app.tga, which was taken after unloading the ditherig application and restarting the PC to ensure that the GPU register states were reset to their default values.
In the resulting comparison images, the first image of the two being compared is used as a blurred background. Red dots indicate pixels that differ. As you can see, spatial dithering most often manifests as something resembling a "checkerboard" pattern.
Note that spatial dithering is predictably absent on white (255, 255, 255). However, on (254, 254, 254), it is present and appears as an alternation of pixels (255, 255, 255) and (254, 254, 254). This can be seen in spatial_dithering.tga (the photo with the girls). You need to check the "white" using any colorimeter application.
As I mentioned above, I also took a screenshot when the ditherig application was not being used. It matched pixel-for-pixel with the screenshot taken after enabling the dithering disable option in the ditherig application. It shows that, by default, dithering is completely absent.
What surprised me: the option to enable temporal dithering also works. This means temporal dithering can be enabled on some Intel iGPUs/GPUs. I suppose this will definitely include all iGPU/GPU based on the Xe architecture (ARC A, Intel iGPUs from the 11th to 14th CPU generations). I can't say about others. If needed, I can compress and upload video files (the original files are very large), which demonstrate the presence of temporal dithering when the corresponding option is enabled.