Hi "4:x:y" refers to chroma subsampling, details here: https://en.wikipedia.org/wiki/Chroma_subsampling. With "YUV 4:4:4" each pixel has 1 Luma information and 1 Chroma information: 1 Y + 1 Cb + 1 Cr = 24 bits per pixel. In top of that, each of the three components (Y, Cb, Cr) can be stored in a single memory plane (packed format), just like usual RGB formats are. Or components can be stored in 2 (Y + Cb-Cr) or 3 (Y + Cb + Cr) memory planes. The combination of the chroma subsampling and the number of planes, defines a pixel format. The problem is that each sub-system (DRM, V4L2, GStreamer, ...) uses its own constants with unfortunately unconsistent names across them. Let's consider the YUV 4:4:4 with three planes format: DRM = DRM_FORMAT_YUV444 V4L2 = V4L2_PIX_FMT_YUV444M GStreamer = GST_VIDEO_FORMAT_Y444 As you can see, although all of them specify the same pixel format, the names are quite different. And regarding V4L2_PIX_FMT_YUV444 (not ending with "M"), it defines another format with the following specifications: - YUV packed - 4:4:4 chroma sampling - Alpha (when supported by driver) - 4 (not 8) bits per component Very different from the "standard" YUV 4:4:4 pixel format. I agree that its name is confusing, but since it is part of the API, we shall consider that it won't be updated. From what I have seen, DRM (maybe because it is a relatively recent 'framework') has a clear definition of the pixel formats. Fabien On 10/27/2016 08:16 AM, Guennadi Liakhovetski wrote: > Hi, > > Looks like the Linux definition of the (packed) YUV444 format contradicts > wikipedia. According to > https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/pixfmt-packed-yuv.html > The Linux V4L2_PIX_FMT_YUV444 format takes 16 bits per pixel, whereas the > wikipedia > https://en.wikipedia.org/wiki/YUV#Converting_between_Y.E2.80.B2UV_and_RGB > says it's 24 bits per pixel. I understand that the wikipedia doesn't have > an absolute authority, but I also saw other sources using the same > definition. So, looks like some confusion is possible. > > Thanks > Guennadi > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
