 Image memory plane

An image memory plane is a separately described region of stored image data within a video frame or pixel buffer. It is a memory-organization concept, distinct from a component plane or a bit plane. One memory plane can contain several interleaved components, while one image can use several memory planes.^[ref]

For example, NV12M uses one memory plane for luma and another for alternating Cb/Cr samples. It therefore has two memory planes but three colour components. NV21M uses the same plane count with the colour-difference pair order reversed. Their 4:2:0 chroma subsampling specifies sample counts; it does not turn the two components in the second plane into separate allocations.

Allocation capacity and video buffer payload also differ. A V4L2 plane descriptor records length, bytesused and a V4L2 plane data offset. In that API, bytesused includes the offset before the actual image data, so the image-data extent isThe allocation size is a separate limit.^[ref]

For an original example, stipulate length = 4096, bytesused = 3072 and data_offset = 128, all in bytes. The image data begin128 bytes after the plane base and span2944 bytes, ending at base offset3072. They occupy neither the full4096-byte allocation nor all3072 bytes preceding that endpoint. The necessary bounds areA consumer must combine these extents with the actual pixel format and framebuffer stride. A plane's capacity alone does not identify where a particular component or row begins.