What's the deal with red and video compression?

Posted:
in General Discussion edited January 2014
Why does virtually all video compression cause red to become extra pixelated? -- more so than all other colors.



Here's just one example: http://www.apple.com/iphone/ipod/ (look at the red stripes on the album art of the U2 song playing)

Comments

  • Reply 1 of 6
    jeffdmjeffdm Posts: 12,946member
    Quote:
    Originally Posted by icfireball View Post


    Why does virtually all video compression cause red to become extra pixelated? -- more so than all other colors.



    Here's just one example: http://www.apple.com/iphone/ipod/ (look at the red stripes on the album art of the U2 song playing)



    It's hard to explain, but often, the colors red and blue aren't given as high of a resolution as green, often 1/4th the resolution of the image. This allows better compression as we see brightness detail a lot more than we can see color detail. The blockiness of blue isn't as visible because we can't actually see very much blue detail. I wish I could find a picture that shows this, I've seen a page and a picture where they really knocked down the resolution of the blue and red channels to demonstrate this.
  • Reply 3 of 6
    jeffdmjeffdm Posts: 12,946member
    Quote:
    Originally Posted by hardeeharhar View Post


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



    I'm pretty sure that's not really a factor here, the blockiness of red shows up when the video is scaled up, the red blocks are larger than the luma blocks, because of what I described above.
  • Reply 4 of 6
    nvidia2008nvidia2008 Posts: 9,262member
    Quote:
    Originally Posted by JeffDM View Post


    It's hard to explain, but often, the colors red and blue aren't given as high of a resolution as green, often 1/4th the resolution of the image. This allows better compression as we see brightness detail a lot more than we can see color detail. The blockiness of blue isn't as visible because we can't actually see very much blue detail. I wish I could find a picture that shows this, I've seen a page and a picture where they really knocked down the resolution of the blue and red channels to demonstrate this.



    When doing web design in the old days of "web safe" palette, you could clearly look at the palette and say, WTF, why is there so much green colours. Actually technically there isn't, because the 256 "web-safe" colours were created by dividing RGB up very evenly. The problem is that human perception of (AFAIK, in this case referring to) green, is not as sensitive as our appreciation of more red-spectrum areas.



    What I want to know is why does H.264 compression absolutely blow chunks (almost literally) when it comes to shadow areas? They need to have a workaround for this.
  • Reply 5 of 6
    Quote:
    Originally Posted by nvidia2008 View Post


    When doing web design in the old days of "web safe" palette, you could clearly look at the palette and say, WTF, why is there so much green colours. Actually technically there isn't, because the 256 "web-safe" colours were created by dividing RGB up very evenly. The problem is that human perception of (AFAIK, in this case referring to) green, is not as sensitive as our appreciation of more red-spectrum areas.



    What I want to know is why does H.264 compression absolutely blow chunks (almost literally) when it comes to shadow areas? They need to have a workaround for this.



    No, humans can distinguish between more shades of green than any other colour. This is why red would receive the most compression, as we can distinguish between fewer shades of red than any other colour (when talking about the three basic additive colours: red, green and blue).



    Subpixel rendering is irrelevant to this topic.
  • Reply 6 of 6
    nvidia2008nvidia2008 Posts: 9,262member
    Quote:
    Originally Posted by max_naylor View Post


    No, humans can distinguish between more shades of green than any other colour. This is why red would receive the most compression, as we can distinguish between fewer shades of red than any other colour (when talking about the three basic additive colours: red, green and blue).



    Subpixel rendering is irrelevant to this topic.



    Hmmm... OK thanks for info. I don't have time to read up further on the RGB -human -perception thing at this stage. I should get round to it sometime hopefully.
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