Converting 10 bit Y'CbCr to 8 bit RGB using vImageConvert_YpCbCrToARGB_GenerateConversion on iOS

Question

Given a CVPixelBuffer with format kCVPixelFormatType_420YpCbCr10BiPlanarVideoRange, I'm trying to generate a corresponding 8-bit RGB frame for further processing. I understand this will be a lossy conversion – the RGB frame will just be used to calculate some descriptive statistics.

I'm basing my conversion on this sample code provided in the Accelerate documentation, which shows how to convert 8-bit BT.601 color samples to RGB.

The core of what I'm trying to do revolves around the vImageConvert_YpCbCrToARGB_GenerateConversion function, which allows you to specify a color conversion matrix, pixel range information, input YpCbCr format, and output ARGB format (see here). So far, I've adapted the sample code in the following ways:

1. I have changed the color conversion matrix. Unfortunately, there doesn't seem to be a built-in constant like kvImage_YpCbCrToARGBMatrix_ITU_R_601_4 for BT.2020. Instead, I've created my own based on the specification:

var colorMatrix = vImage_YpCbCrToARGBMatrix(
            Yp: 1,
            Cr_R: 1.4746,
            Cr_G: -0.5714,
            Cb_G: -0.16455,
            Cb_B: 1.8814
        )

2. I have updated the vImage_YpCbCrPixelRange to (hopefully) account for the 10 bit format:

var pixelRange = vImage_YpCbCrPixelRange(Yp_bias: 64,
                                                 CbCr_bias: 512,
                                                 YpRangeMax: 940,
                                                 CbCrRangeMax: 960,
                                                 YpMax: 255,
                                                 YpMin: 0,
                                                 CbCrMax: 255,
                                                 CbCrMin: 0)

I am not confident about YpMax, YpMin, CbCrMax, or CbCrMin, but the other values should be correct based on the documentation's description of the 10-bit video range format (kCVPixelFormatType_420YpCbCr10BiPlanarVideoRange).

3. The core adjustment/problem (or so I believe): I am trying to change the inYpCbCrType to reflect the actual format of my CVPixelBuffer. The sample code uses kvImage422CbYpCrYp8, but I assume I'm looking for something like kvImage420CbYpCrYp10 (which doesn't exist). As far as I can tell, the only options are listed here. I have tried some of the 10 bit formats (4:2:2 and 4:4:4), but the results are pretty wonky (grainy with gaps and mostly yellow). Of course, that's probably expected since I'm specifying a random chroma subsampling ratio, not the actual 4:2:0 used in my pixel buffer.

I believe what I'm trying to do is possible; at least, the attached table in the documentation for vImageConvert_YpCbCrToARGB_GenerateConversion indicates that YUV10 to RGB8 is supported (though it doesn't say for which chroma subsampling ratios).

With that background out of the way, my core questions are as follows:

• Is what I'm trying to do supported?
• If so, which vImageYpCbCrType am I supposed to use?
• If that's the wrong question, what workflow should I be using instead?

I am relatively new to image processing (I mostly deal with audio signal processing), so please let me know if I have any fundamental misunderstandings in addition to the described issues. Thanks!