[Interest] QVideoFrame and YUV question

[Jason H]

http://en.wikipedia.org/wiki/YUV


"The YPbPr color model used in analog component video and its digital version YCbCr used in digital video are more or less derived from it, and are sometimes called Y'UV. (CB/PB and CR/PRare deviations from grey on blue–yellow and red–cyan axes, whereas U and V are blue–luminance and red–luminance differences.) The Y'IQ color space used in the analog NTSC television broadcasting system is related to it, although in a more complex way."


________________________________
 From: Thiago Macieira <thiago.macieira at intel.com>
To: interest at qt-project.org 
Sent: Friday, March 14, 2014 12:22 PM
Subject: Re: [Interest] QVideoFrame and YUV question
 

Em sex 14 mar 2014, às 08:47:15, Jason H escreveu:
> The frame is not laid out like RGB. This is for legacy reasons. Black and
> White TV presented a black and white frame (Y) when color TV was added, it
> was added in a backwards-compatible way

This has nothing to do with black & white TV. Digital image formats were 
invented way after colour TV.

The reason why Y is sampled per pixel whereas U and V aren't is because the 
eye isn't as sensitive to colour as it is to luminosity. By using one U and 
one V for 4 pixels, we reduce the amount of data from 12 values to 6 in each 
2x2 block -- that is, half the amount of data.

There are some other YUV formats that lay out data differently, including all 
the chrominance values, like YUV 4:4:4.
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center


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