determine yuv pixel format in capture use.case

[Christian Günther]

Hi there,

I use yuv image format for image capture to avoid jpeg compression. Sadly there is no uncrompressed rgb format here. At the moment i convert therefore the yuv using renderscript. I try to migrate to libyuv with this project:
https://github.com/crow-misia/libyuv-android

Therefore i need to know the underlying pixel format that i get from camerax in the yuv buffer. In all my local tests (Galaxy S8 and Redmi Note 10 Pro) the image format reports me:
image.getFormat() == ImageFormat.YUV_420_888 --> true
nevertheless it seems that the internal format is nv21 instead of i420_8888 buffer type to get correct conversions. The the question that comes up in my mind is: "How do i robustly determine which pixel-format is really internally used, to be able to select the correct corresponding conversion function?"

best,

Christian

[Kailiang Chen]

Hi Christian,

The ImageFormat.YUV_420_888 is a generic YCbCr forma, capable of describing any 4:2:0 chroma-subsampled planar or semiplanar buffer (but not fully interleaved), with 8 bits per color sample.

It only guarantees

1. that plane #0 is always Y, plane #1 is always U (Cb), and plane #2 is always V (Cr)

2. pixel stride is always 1 in yPlane.getPixelStride()

3. uPlane.getRowStride() == vPlane.getRowStride() and uPlane.getPixelStride() == vPlane.getPixelStride()

https://developer.android.com/reference/android/graphics/ImageFormat#YUV_420_888

So YUV_420_888 could be nv21, nv12, I420, etc,.

To determine which pixel format is being used internally, you could refer to the code here 

https://github.com/crow-misia/libyuv-android/blob/main/core/deps/libyuv/source/convert_argb.cc#L4310

Unfortunately there is no public API to determine the format yet.

Best,

Kailiang

[Christian Günther]

Thanks a lot for the clarification here.