What is 4:2:2 I Frame?

Re: What is 4:2:2 I Frame?

I Frame.. in an Interframe compression scheme..

is also known as a keyframe... this frame contains a full frame.. or an entire picture.

P-Frames(Predicted Frames) and B-Frames(Bi-Directional Frames) draw on the information from an I-Frame to make up parts of their own frame.

4:2:2 just refers to the colour space of the codec, It doesn't have much to do with the I-Frame... (although I am sure algorithm wise, it has a lot to do.. but thats a whole other can of worms..)

anyone correct me if I am wrong... it is late.
 
Re: What is 4:2:2 I Frame?

Can anyone give me a reference on the meaning of the three numbers separated by colons are (e.g., 4:2:2). I see this used all the time but cannot find a specific reference on what the meaning of the numbers is? Thanks much.
 
Re: What is 4:2:2 I Frame?

4:1:1 - for every 4 pixels, there is 1 colour sample on the x axis, and one colour sample on the y axis.

the 1:1 refers to the horizontal/vertical amount of color pixels that occupy the 4x4 block of pixels.

hope that explains it a bit
 
Re: What is 4:2:2 I Frame?

The numbers stand for the components in a component video signal: Y, Cr, and Cb. They refer to how frequently those elements are sampled per scan line, per group of four pixels.

4:1:1 has one of each color sample for every group of 4 luminance samples, and that happens on every scan line.

4:2:0 has two color samples of one of the components on each scan lines per group of four luminance samples, but *no* color samples of that component on the odd scan lines. So on an even 4:2:0 scan line you'll find four luma (Y) samples, and two Cr samples, but no Cb samples. On an odd 4:2:0 scan line you'll find four Y samples, no Cr samples, but two Cb samples.

Both methods have 2 color samples per 4x2 block of pixels, just in a different pattern. 4:2:0 is used by PAL DV and by MPEG-2 and HDV, 4:1:1 is used by NTSC DV.

More reading is available at http://www.adamwilt.com/pix-sampling.html
 
Re: What is 4:2:2 I Frame?

Both methods have 2 color samples per 4x2 block of pixels, just in a different pattern.  4:2:0 is used by PAL DV and by MPEG-2 and HDV, 4:1:1 is used by NTSC DV.


How "badly" is the colour samples effected when converting PAL DV to/from NTSC DV with software?

THX
 
Re: What is 4:2:2 I Frame?

There's theory, and then there's reality. I suggest if you want to see, download the demo version of DVFilm's Atlantis software, and then you can see what the reality is.
 
Re: What is 4:2:2 I Frame?

Thanks all for the answers. I can't tell you how useful I find this site. I really appreciate "those in the know" taking time out to answer the newbie questions.
 
Re: What is 4:2:2 I Frame?

Thanks again Barry and Loki for your replies. Now that I sort of understand the Luma and color sampling designations, this brings another question to mind. Suppose you recorded video in DVCPRO50 format (4:2:2). This is presumably "better" because of the higher frequency sampling of Cr and Cb. Can this be edited on a PC using Vegas just like NTSC DV (4:1:1)? And then, when the video is burned to dvd MPEG2 (4:2:0 ??), is there a problem with rendering the 4:2:2 format as opposed to the usual NTSC DV 4:1:1 format? Maybe another way to pose this question: Is the "better" video quality of DVCPRO50 lost if you ultimately edit and then burn to dvd?
 
Re: What is 4:2:2 I Frame?

I don't believe Vegas currently supports the DVCPRO50 codec, but maybe it does. I'm sure other editors (like FCP) do.

When burned to DVD, it's likely that you'll get a better-looking final product from 4:2:2 down to 4:2:0 than you would from 4:1:1 down to 4:2:0, but that's just speculation, I'd like to run some real-world results before declaring that it would be so.
 
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