Colorspace packing formats

Could someone briefly explain what the various packing formats for colorspace are and how they relate to the colorspaces themselves? ie: What are 4:4:4, 4:2:2, 4:2:0 formats? How do they relate to colorspaces like RGB32, YUV2 or YV12?

and all links in

RGB and YUV are colorspaces. RGB32 is a specific format for RGB, where it uses 1 byte for red, 1 byte for green, 1 byte for blue, and 1 byte that's unused (or is sometimes used for alpha). YUY2 and YV12 are specific formats of YUV. YUY2 uses 4:2:2 subsampling, consuming an average of 16 bits per pixel, and YV12 uses 4:2:0, consuming an average of 12 bits per pixel. Explanation of subsampling formats:

Ah, got it. Thanks

Since we're already on that topic... I have some more dumb questions that have been nagging me for some time now. In RGB I know that each channel can take a variety of 256 values in total, hence the resulting 8 bit. In YUV each channel is represented with a value from 0-4 like in 4:4:4 , 4:2:2 , etc. Obviously the 4 does not represent the maximum of bits it can hold, since only 16 possible values for a channel would result in quite a poor picture... So what does this 4 stand for? And YUY2 is 16 bit, okay. That makes sense, when we say that 4*2*2 = 16, but why is YV12 (4:2:0) 12 bits then? Oh, and my last question has a bit to do with my bad memory...don't know if I recall it correctly, but in a former in-depth discussion of DVD-Video, it was stated that DVDs don't exactly use YV12 but rather a 4:2:0 colorspace with the chroma channels switched (UYUY ? ) Was that correct? And if yes, I obviously had never trouble in dealing with DVDs + Avisynth, so does Avisynth handle this conversion internally or any of the plugins I use to import DVD-footage? Hope I made some sense.

The numbering scheme dates back to the 1980's I think, but their historical usage seems a bit obscure today. I did find some interesting explanations on the web:

uhm. I've gotten some kind of flash in my mind while reading your post, fcchandler! SECAM! SECAM is a color-system that is based on the 625-lines 50 Hertz blackwhite television (the same like PAL is based on) BUT SECAM is transferring its chroma components sequential, which means: every even (big assumption!) line of a FIELD transfers the U and every odd line of a FIELD transfers the V this is exactly, how the chroma sampling of 'PAL'-DV works. knows the devil why... I am afraid! but maybe I am way to tired and throwed some (mis)information together...

I really doubt that. Both assumptions. (But I am not absolutely sure about them) SECAM is NOT a production format. It is a broadcast format. This means: Production is done on very common 625-50 Equipment with 4:4:4 or at least 4:2:2 subsampling. no color encoding scheme like pal or secam is used here. the format-encoding (PAL,SECAM,NTSC) is the very last step of this production -> storing -> delivering -> encoding & brodcasting chain. the encoding is done withing the broadcasting station. or the signal comes preprocessed to the broadcasting station. but the encoder is feed with a component YUV analogue signal. so noone in production works with composite video signals like SECAM, PAL or NTSC. It's all YUV.