Explanation of YUV X:X:X notation

thewebchat · 2nd August 2009, 02:45

I know that the different YUV chroma sub-sampling formats are given the notation 4:x:x, with YUY2 being 4:2:2 and YV12 being 4:2:0. My question is, what does this numerical notation indicate? I have read the YUV article on Wikipedia, but it does not explain what this notation means.

linyx · 2nd August 2009, 04:00

I'm a noob, so this might be wrong, But:

The numbers represent the vertical resolutions given to the Luminance and Chrominance of a color space.

The first number usually represents the Luminance (Y), the second represents the Blue minus the Luminance (Cb), while the third represents the Red minus the Luminance (Cr). Green minus the Luminance is not stored becuase it can be calculated by subtracting the Cb & Cr from Y.

So for something like 4:2:2, each pixel would have a Luminance sample, but only 2 out of every four (vertical & horizontal; so truly only 1/4 of the pixels are given a color sample) would have a Cb and Cr sample. The exception is 4:2:0 which should really be 4:0:0

It can be illustrated like such for a 4:2:0 colorspace:
0=Y
1=Y+Cb+Cr

Code:

1    0

0    0

4:4:4 would be:

Code:

1    1

1    1

Most of this was roughly copied from "H.264 and MPEG-4 Video Compression."

TinTime · 2nd August 2009, 11:17

The first digit represents the number of horizontal pixels we're considering. Although this can have any value it always seems to be 4. It's also implicit that we're looking at two lines at a time. So with the first digit as 4 it means that we have a 4x2 (horizontal by vertical) block of pixels.

The second digit indicates how many chroma samples are taken from the top line of each block of pixels, and the third digit indicates how many are taken from the bottom line.

e.g. 4:2:2 results in each chroma sample representing a 2x1 block of pixels - 2 samples per line of four pixels.

Code:

x represents a chroma sample, o doesn't

xo|xo
xo|xo

4:2:0 results in each chroma sample representing a 2x2 block of pixels as the bottom line value is 0.

Code:

xo|xo
oo|oo

And 4:1:1 would be:

Code:

xooo
xooo

Hope this makes sense!

thewebchat · 2nd August 2009, 14:42

Thank you, TinTime, your post cleared this up for me.

unnikrisb4u · 3rd August 2009, 04:17

That was a wonderful explanation. Thanks for Information

2nd August 2009, 02:45	#1 \| Link
thewebchat Advanced Blogging Join Date: May 2009 Posts: 480	Explanation of YUV X:X:X notation I know that the different YUV chroma sub-sampling formats are given the notation 4:x:x, with YUY2 being 4:2:2 and YV12 being 4:2:0. My question is, what does this numerical notation indicate? I have read the YUV article on Wikipedia, but it does not explain what this notation means.

2nd August 2009, 04:00	#2 \| Link
linyx Un-Registered User Join Date: Mar 2008 Location: Audio Stream - 0x80 Posts: 341	I'm a noob, so this might be wrong, But: The numbers represent the vertical resolutions given to the Luminance and Chrominance of a color space. The first number usually represents the Luminance (Y), the second represents the Blue minus the Luminance (Cb), while the third represents the Red minus the Luminance (Cr). Green minus the Luminance is not stored becuase it can be calculated by subtracting the Cb & Cr from Y. So for something like 4:2:2, each pixel would have a Luminance sample, but only 2 out of every four (vertical & horizontal; so truly only 1/4 of the pixels are given a color sample) would have a Cb and Cr sample. The exception is 4:2:0 which should really be 4:0:0 It can be illustrated like such for a 4:2:0 colorspace: 0=Y 1=Y+Cb+Cr Code: 1 0 0 0 4:4:4 would be: Code: 1 1 1 1 Most of this was roughly copied from "H.264 and MPEG-4 Video Compression."

2nd August 2009, 11:17	#3 \| Link
TinTime Registered User Join Date: Jan 2009 Location: UK Posts: 403	The first digit represents the number of horizontal pixels we're considering. Although this can have any value it always seems to be 4. It's also implicit that we're looking at two lines at a time. So with the first digit as 4 it means that we have a 4x2 (horizontal by vertical) block of pixels. The second digit indicates how many chroma samples are taken from the top line of each block of pixels, and the third digit indicates how many are taken from the bottom line. e.g. 4:2:2 results in each chroma sample representing a 2x1 block of pixels - 2 samples per line of four pixels. Code: x represents a chroma sample, o doesn't xo\|xo xo\|xo 4:2:0 results in each chroma sample representing a 2x2 block of pixels as the bottom line value is 0. Code: xo\|xo oo\|oo And 4:1:1 would be: Code: xooo xooo Hope this makes sense! Last edited by TinTime; 2nd August 2009 at 11:22. Reason: Added another example

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2nd August 2009, 14:42	#4 \| Link
thewebchat Advanced Blogging Join Date: May 2009 Posts: 480	Thank you, TinTime, your post cleared this up for me.

3rd August 2009, 04:17	#5 \| Link
unnikrisb4u Registered User Join Date: Nov 2008 Location: India Posts: 13	That was a wonderful explanation. Thanks for Information