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Thread: Chroma subsampling explained

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    Gaming Wizard StarBound's Avatar
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    Cool Chroma subsampling explained

    So these are a few videos that I found regarding the subject. Obviously 4:4:4 would be a dream but sadly 4:2:2 will have to do. Also explains 4:2:0.







    The one video mentions you can work without colour data but you cannot work without luminescence data. I've actually seen this mentioned with another video when explaining NTSC and how it was used to create colour over a broadcast.

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    Gaming Wizard KenMasters's Avatar
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    Quote Originally Posted by StarBound View Post
    So these are a few videos that I found regarding the subject. Obviously 4:4:4 would be a dream but sadly 4:2:2 will have to do. Also explains 4:2:0.
    If you understand the concept you'd know it's nothing sad (especially at Ultra HD resolutions), also we don't use 4:2:2 these days, most content is 4:2:0

    EDIT: Flip between the two on your PS4 Pro and see how much difference it makes to the home screen.
    Last edited by KenMasters; July 26th, 2018 at 07:13 AM.

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    Gaming Wizard StarBound's Avatar
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    I think I am missing the point then. 4 pixels by 2 rows to 8 pixels in total.

    4:4:4 means 4 pixels in the first row has 4 distinct colours and 4 distinct colours in the 2nd row.
    4:2:2 means 4 pixels in the first row with 2 distinct colours and 2 distinct colours in the 2nd row.
    4:2:0 means 4 pixels in the first row with 2 distinct colours and row 2 just copies the first row.

    Well that is my understanding.
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    Gaming Wizard KenMasters's Avatar
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    Quote Originally Posted by StarBound View Post
    I think I am missing the point then. 4 pixels by 2 rows to 8 pixels in total.

    4:4:4 means 4 pixels in the first row has 4 distinct colours and 4 distinct colours in the 2nd row.
    4:2:2 means 4 pixels in the first row with 2 distinct colours and 2 distinct colours in the 2nd row.
    4:2:0 means 4 pixels in the first row with 2 distinct colours and row 2 just copies the first row.

    Well that is my understanding.
    You have to understand that the images are a conceptual representation to illustrate the various sampling schemes, not what you're getting displayed on your screen. We are much more sensitive to contrast than we are to colour, for that reason the picture on screen is rendered in black and white in full resolution, a lower resolution colour layer is then placed on top of that (there are not holes in the colour as the visual representations of the schemes might lead you to believe, they are blended together and then overlayed).

    All the detail comes from the greyscale image, that's what creates the definition, the colour doesn't have to be full resolution on top of that as our sensitivity to it is low. If you were looking at pixel width colour text on a computer monitor, not having full chroma would be an issue as you would see a slight transitional colour overlap, but in film or game content, and with text typically spanning multiple pixel widths, its not something you're going to pick up on. You really have to get right up to the screen and look at very specific elements that don't commonly crop up in an image to identify chroma upsampling.
    Last edited by KenMasters; July 26th, 2018 at 11:26 AM.

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    Gaming Wizard StarBound's Avatar
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    When you put it like that the only way I can think of is currently our pixels are made up of 3 sub pixels (is that right?) which are red, blue and green. If our senses were extremely sharp we would be able to distinguish between all of them meaning we would see a red blue and green mess if we looked at our current displays. The mix of brightness and colour blends into each other creating our current image or illusion of it.

    So instead of having 4:4:4 giving us the best pixel perfect picture there is we get 4:2:2 or 4:2:0 because to our vision the colour is hidden or indistinguishable?
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    Gaming Wizard KenMasters's Avatar
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    Quote Originally Posted by StarBound View Post
    When you put it like that the only way I can think of is currently our pixels are made up of 3 sub pixels (is that right?) which are red, blue and green.
    Right - though in the case of commercial OLEDs, there's a fourth white subpixel.

    Quote Originally Posted by StarBound View Post
    If our senses were extremely sharp we would be able to distinguish between all of them meaning we would see a red blue and green mess if we looked at our current displays.
    No, because it's not a mess. Our own eyes are tristimulus devices, our vision is comprised of red, green and blue, for which we have separate detectors.

    The colour layer is softer, but that doesn't matter because the greyscale image is sharp. The base layer of your image is this:

    B&W.jpg

    Above which is placed the lower resolution colour overlay (I've placed the colour on a 50% grey backdrop to give it a backing so you can see it):

    Colour.jpg

    As you can see, definition is not exactly vital here. Combine these two layers and you get this:

    Image.jpg

    Quote Originally Posted by StarBound View Post
    The mix of brightness and colour blends into each other creating our current image or illusion of it.

    So instead of having 4:4:4 giving us the best pixel perfect picture there is we get 4:2:2 or 4:2:0 because to our vision the colour is hidden or indistinguishable?
    Well, Y (luma), the greyscale that renders the first image I posted, blends with C (chroma) to create the final image. Luma is kept full resolution, because that is where the detail lies, as you can see, colour is far less defined to our eyes. This is due to the balance of cones vs rods in our eyes that affect our sensitivity to colour vs contrast respectively.
    Last edited by KenMasters; July 26th, 2018 at 01:14 PM.

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    Gaming Wizard StarBound's Avatar
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    And there are a few of us that has succumb to the taste of OLED.

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