The Apple Pro Display XDR gets 38.9 Gbps over Thunderbolt for GPUs that don't support DSC by transmitting two separate HBR3 signals for a dual tile mode for each tile). There's no way to transmit more than HBR3 (25.92 Gbps) over Thunderbolt. DSC compresses to 12bpp by default in macOS but that might be modifiable using a preference.Īt 12bpp, you can reduce the DisplayPort link rate to HBR2 (17.28 Gbps) and still achieve up to 1440 MHz (minus overhead for FEC which DSC usually requires). To transmit them from an HBR3 source, DSC is required. Those all exceed the HBR3 limit of 25.92 Gbps except the CVT-RB2 8bpc mode which might be too close to the limit.
Some displays may take a 10bpc input and use some method of displaying that on a 8bpc panel, such as FRC
Outside the framebuffer on the way from the GPU to the display pixels, other color transformations may occur. Maybe taking a screenshot and then examining the pixels using a color histogram can detect if it was displaying at 10bpc without dithering, at least in the framebuffer. Some apps might only display 8bpc but they might dither the image so it looks like 10bpc. You might get a different result using Quick Look in Finder.app versus Preview.app. The next problem is how to display the image. It might be impossible to notice banding in the 10bpc row which is above the 8bpc row. For each band of 6bpc you should be able to see 4 bands of 8bpc. For 8bpc you may be able to see the banding by zooming in. With the image generated by the above code, you should be able to see gradients of 12bpc, 10bpc, 8bpc, 6bpc of each color (grey, red, green, blue, yellow, cyan, magenta).
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