What do these video formats mean?

[Videogamer555]

I've looked at the glosary but didn't find all my answers.

What I did find was that in YUV color space
4:4:4 is 4 pixels of Y data for every 4 pixels U data and every 4 pixels of V data
4:2:2 and 4:1:1 also are ratios like this.

But then there's this mysterious one
4:2:0 which seems to mean 4 Y for every 2 U, but absolutely no V data. But that doesn't make sense, due to the fact that you need 3 pieces of data to construct a color image. If V is missing, then that means you have just significantly reduced the number of colors that can be displayed. So what does it mean?

Then also you have formats specified like this.
YUV
UYVY
YUYV
This seems to suggest the order that the data is stored in the file, but then again I run into a mysterious one like
YUY2 and I don't know what this means. Again, where is the V data? And what does the number 2 mean?
And what's i420?

Someone please explain these things to me.

[jagabo]

4:2:0 is the same as 4:1:1 in the sense that there are 1/4 as manu U and V as Y values. But with 4:2:0 they are half in each dimension instead of 1/4 in one dimension. The different names are to differentiate the two:

4:1:1 -- 720x480 Y plane, 180x480 U and V planes (typical in NTSC DV)
4:2:0 -- 720x480 Y plane, 260x240 U and V planes (typical in DVD)

YUV is just the generic name for video in Y, U and V format.

UYVY, YUYV, YUY2, etc. are just different orderings of the Y, U, and V values.

i420 is similar to YV12, 4:2:0 chroma subsampling except the U and V planes are reversed.

http://fourcc.org/yuv.php