IYUV or YV12 colorspace?

Magno · 19th May 2004, 01:24

I have been searching the forum for two hours to get information about a doubt i have about colorspace converisions and i haven't been able to understand this...

MPEG2DEC3.dll outputs the image in YV12 format nativelly, but the colorspace used in MPEG-2 4:2:0 is, actually, IYUV (or I420, as you like) so... where is the point about getting the output in YV12, in which the chroma components are changed in order (before V, then U)?

I suppose that the YUY2 output is used with MPEG-2 sources which have 4:2:2 profile in them. Maybe am i wrong?

Wilbert · 19th May 2004, 09:04

Quote:

MPEG2DEC3.dll outputs the image in YV12 format nativelly, but the colorspace used in MPEG-2 4:2:0 is, actually, IYUV (or I420, as you like) so...

Indeed. Well, I think that mpeg2dec3 outputs I420, and AviSynth converts it to YV12 internally. But, the user won't notice this.

Quote:

where is the point about getting the output in YV12, in which the chroma components are changed in order (before V, then U)?

Good one. Maybe it is stored in DivX/Xvid as YV12 (and not I420). But, I'm not sure.

Quote:

I suppose that the YUY2 output is used with MPEG-2 sources which have 4:2:2 profile in them. Maybe am i wrong?

Maybe Neuron2 can comment on this. Btw, I have never seen such streams.

Magno · 19th May 2004, 09:52

I am developing a program which debugs a MPEG-2 stream, in any level and profile, and so, i have some 4:2:2 streams to test the program.
If anyone would like to take a look at them, contact me

trevlac · 19th May 2004, 14:21

Hi,

I just wanted to clarify because there is a common misuse of terms. As a newbie this confused the heck out of me. Still does.

A color space is a mathimatical description of color. Most contain 3 components such as RGB, HSV, YCbCr. You can convert between these. Each component is basically a variable in an equation.

IYUY and YUV12 are pixel formats. They both reside in the YCbCr color space.

Especially within the YCbCr color space you find a number of different flavors. These are due to:

1) Subsampling such as 4:2:0 vs 4:2:2 vs 4:1:1 etc ...

2) Bit depth such as 8 or 10 or 15

3) Pixel storage format aka (I believe) FourCC. IYUV or YV12

So ... there is no color space conversion from IYUV to YV12. I don't even think it would be proper to call up sampling or down sampling a color space conversion .... YCbCr 4:2:0 to YCbCr 4:2:2 etc.

Here are some nice M$ article on the topic...
http://support.microsoft.com/default...b;EN-US;294880
http://msdn.microsoft.com/library/de...yuvformats.asp

PS: YUV is an unfortunate term that describes many things. In it's general use, YUV referrs to the YCbCr color space in digital. YUV is also a reference to the PAL analog color space. Yuv is a reference to the color science Luminance/chromiance, which is not the same as YUV in video. Poynton goes on and on about this here: http://www.poynton.com/PDFs/YUV_and_...ce_harmful.pdf

PPS: Unfortunately there do seem to be a number of YCbCr color spaces. SMPTE vs 601 vs 709 I believe. The difference is due to what combination of colors is considered to make up the Y component. The difference exists because YCbCr is intended to be projected back thru a display device (your monitor or TV). Standards changed as monitors changed. 709 is for modern monitors, but 601 is what is used for non HD video.

This was ment to help future readers ... but hey ... I don't work in the field. Just read about it and play. Maybe I got the details wrong.

Wilbert · 19th May 2004, 15:32

Quote:

So ... there is no color space conversion from IYUV to YV12

Details ... "color format conversion" if you prefer

19th May 2004, 01:24	#1 \| Link
Magno Registered User Join Date: Feb 2003 Posts: 73	IYUV or YV12 colorspace? I have been searching the forum for two hours to get information about a doubt i have about colorspace converisions and i haven't been able to understand this... MPEG2DEC3.dll outputs the image in YV12 format nativelly, but the colorspace used in MPEG-2 4:2:0 is, actually, IYUV (or I420, as you like) so... where is the point about getting the output in YV12, in which the chroma components are changed in order (before V, then U)? I suppose that the YUY2 output is used with MPEG-2 sources which have 4:2:2 profile in them. Maybe am i wrong?

19th May 2004, 09:52	#3 \| Link
Magno Registered User Join Date: Feb 2003 Posts: 73	I am developing a program which debugs a MPEG-2 stream, in any level and profile, and so, i have some 4:2:2 streams to test the program. If anyone would like to take a look at them, contact me

19th May 2004, 14:21	#4 \| Link
trevlac budala Join Date: Oct 2003 Location: U.S. Posts: 545	Hi, I just wanted to clarify because there is a common misuse of terms. As a newbie this confused the heck out of me. Still does. A color space is a mathimatical description of color. Most contain 3 components such as RGB, HSV, YCbCr. You can convert between these. Each component is basically a variable in an equation. IYUY and YUV12 are pixel formats. They both reside in the YCbCr color space. Especially within the YCbCr color space you find a number of different flavors. These are due to: 1) Subsampling such as 4:2:0 vs 4:2:2 vs 4:1:1 etc ... 2) Bit depth such as 8 or 10 or 15 3) Pixel storage format aka (I believe) FourCC. IYUV or YV12 So ... there is no color space conversion from IYUV to YV12. I don't even think it would be proper to call up sampling or down sampling a color space conversion .... YCbCr 4:2:0 to YCbCr 4:2:2 etc. Here are some nice M$ article on the topic... http://support.microsoft.com/default...b;EN-US;294880 http://msdn.microsoft.com/library/de...yuvformats.asp PS: YUV is an unfortunate term that describes many things. In it's general use, YUV referrs to the YCbCr color space in digital. YUV is also a reference to the PAL analog color space. Yuv is a reference to the color science Luminance/chromiance, which is not the same as YUV in video. Poynton goes on and on about this here: http://www.poynton.com/PDFs/YUV_and_...ce_harmful.pdf PPS: Unfortunately there do seem to be a number of YCbCr color spaces. SMPTE vs 601 vs 709 I believe. The difference is due to what combination of colors is considered to make up the Y component. The difference exists because YCbCr is intended to be projected back thru a display device (your monitor or TV). Standards changed as monitors changed. 709 is for modern monitors, but 601 is what is used for non HD video. This was ment to help future readers ... but hey ... I don't work in the field. Just read about it and play. Maybe I got the details wrong.