2.7.27. V4L2_PIX_FMT_NV12 (‘NV12’), V4L2_PIX_FMT_NV21 (‘NV21’), V4L2_PIX_FMT_NV12_COL128

V4L2_PIX_FMT_NV21 Formats with ½ horizontal and vertical chroma resolution, also known as YUV 4:2:0. One luminance and one chrominance plane with alternating chroma samples as opposed to V4L2_PIX_FMT_YVU420

2.7.27.1. Description

These are two-plane versions of the YUV 4:2:0 format. The three components are separated into two sub-images or planes. The Y plane is first. The Y plane has one byte per pixel. For V4L2_PIX_FMT_NV12, a combined CbCr plane immediately follows the Y plane in memory. The CbCr plane is the same width, in bytes, as the Y plane (and of the image), but is half as tall in pixels. Each CbCr pair belongs to four pixels. For example, Cb0/Cr0 belongs to Y’00, Y’01, Y’10, Y’11. V4L2_PIX_FMT_NV21 is the same except the Cb and Cr bytes are swapped, the CrCb plane starts with a Cr byte.

If the Y plane has pad bytes after each row, then the CbCr plane has as many pad bytes after its rows.

V4L2_PIX_FMT_NV12_COL128 is the tiled version of V4L2_PIX_FMT_NV12 with the image broken down into 128 pixel wide columns of Y followed by the associated combined CbCr plane. The normal bytesperline is effectively fixed at 128. However the format requires knowledge of the stride between columns, therefore the bytesperline value has been repurposed to denote the number of 128 byte long lines between the start of each column.

Byte Order. Each cell is one byte.

start + 0:

Y’00

Y’01

Y’02

Y’03

start + 4:

Y’10

Y’11

Y’12

Y’13

start + 8:

Y’20

Y’21

Y’22

Y’23

start + 12:

Y’30

Y’31

Y’32

Y’33

start + 16:

Cb00

Cr00

Cb01

Cr01

start + 20:

Cb10

Cr10

Cb11

Cr11

Color Sample Location:

0

1

2

3

0

Y

Y

Y

Y

C

C

1

Y

Y

Y

Y

2

Y

Y

Y

Y

C

C

3

Y

Y

Y

Y