How seperate y-planar, u-planar and uv-planar from yuv bi planar in ios?

Question

In application i used AVCaptureVideo. i got video in kCVPixelFormatType_420YpCbCr8BiPlanarFullRange format.

now i am getting y-planar and uv-planar from imagebuffer.

  CVPlanarPixelBufferInfo_YCbCrBiPlanar *planar = CVPixelBufferGetBaseAddress(imageBuffer);

    size_t y-offset = NSSwapBigLongToHost(planar->componentInfoY.offset);
    size_t uv-offset = NSSwapBigLongToHost(planar->componentInfoCbCr.offset);

here yuv is biplanar format(y+UV).

what is UV-planar? is this uuuu,yyyy format or uvuvuvuv format? How to i get u-planar and y-planar seperatly?

can any one pls help me?

The lack of intentional vagueness in this Q and A is refreshing. — , Apr 03 '14 at 23:37

score 5 · Accepted Answer · answered Nov 19 '12 at 23:32

5

The Y plane represents the luminance component, and the UV plane represents the Cb and Cr chroma components.

In the case of kCVPixelFormatType_420YpCbCr8BiPlanarFullRange format, you will find the luma plane is 8bpp with the same dimensions as your video, your chroma plane will be 16bpp, but only a quarter of the size of the original video. You will have one Cb and one Cr component per pixel on this plane.

so if your input video is 352x288, your Y plane will be 352x288 8bpp, and your CbCr 176x144 16bpp. This works out to be about the same amount of data as a 12bpp 352x288 image, half what would be required for RGB888 and still less than RGB565.

So in the buffer, Y will look like this [YYYYY . . . ] and UV [UVUVUVUVUV . . .]

vs RGB being, of course, [RGBRGBRGB . . . ]

answered Nov 19 '12 at 23:32

jgh

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Why does the UV plane half a quarter of the number of pixels in the Y plane? – mrplants Apr 01 '15 at 00:46
there is 1 u and 1 v pixel for every 4 pixels of y. Hence the size of u and v planes is quarter of the size of y – Shravya Boggarapu Apr 26 '16 at 10:52
The resolution of the UV planes are specified by the chroma subsampling name. In this case it is 420. There was supposed to be some logic to this number, but that got lost when they started halving the vertical resolution. 420 simply means there are 2x2 luma pixels for every 1 chroma red and chroma blue pixel. The other thing to worry about with vertical subsampling is interlaced frames, the 2x2 is field based, not frame based so needs to be handled differently than progressive. Other values can be: 444 no subsampling, 422 2 horizontal luma for 1 chroma. – silicontrip May 30 '20 at 22:24

score 0 · Answer 2 · edited Nov 29 '17 at 02:45

Below code copy yuv data from pixelBuffer whose format is kCVPixelFormatType_420YpCbCr8BiPlanarFullRange.

CVPixelBufferLockBaseAddress(pixelBuffer, 0);

size_t pixelWidth = CVPixelBufferGetWidth(pixelBuffer);
size_t pixelHeight = CVPixelBufferGetHeight(pixelBuffer);
// y bite size
size_t y_size = pixelWidth * pixelHeight;
// uv bite size
size_t uv_size = y_size / 2;
uint8_t *yuv_frame = malloc(uv_size + y_size);
// get base address of y
uint8_t *y_frame = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0);
// copy y data
memcpy(yuv_frame, y_frame, y_size);
// get base address of uv
uint8_t *uv_frame = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 1);
// copy uv data
memcpy(yuv_frame + y_size, uv_frame, uv_size);

CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

How seperate y-planar, u-planar and uv-planar from yuv bi planar in ios?

2 Answers2

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