4K to 1080P 4:4:4

Discussion in 'Open Discussion' started by D7k1, Oct 10, 2016.

  1. D7k1

    D7k1 Mu-43 Top Veteran

    691
    Nov 18, 2013

    D7K
    asked on 10/10/2016, 12:14 PM
    Have you seen this:

    http://www.eoshd.com/2014/02/discovery-4k-8bit-420-panasonic-gh4-converts-1080p-10bit-444/

    I did a test with 4K from my Gx8 and it appears to be much better than rendering to any of the 4:2:0 codecs.



    Here is a quote from the OP at DPR:



    "

    I guess that depends on whether you're a GH3/GH4 user or an Oly user, I certainly think that if Panny stays a part of the forum and they don't split (which IMHO is sensible) then video questions are fine, although a [video] tag (at the start of the subject) like the one suggested for Equivalence might enable people who don't have an interest to skip them.

    Oh and thanks for pointing out there's a new Cliptoolz, although with a different name, I thought they had stopped developing it.

    As to the original question then scaling a 4k image to 2k (i.e. by 2x in H and V and 4x overall) will certainly increase the information content. Remember if you average four values (e.g. with 7,9,9,10 you get 8.75) you get two extra "bits" of information (from resolution of 1 to 0.25, although not as perfectly if did it at the analogue level, they might have started off as 7.4, 9.2, 8.75, 10.3 -> 8.91 -> 9 at 0.25 resolution).

    For colour 4:2:0 gives half the chroma resolution in both x and y and we're halving the x and y resolution. So you go from a chroma sample per 4 (2x2) pixels to one per pixel. 4:4:4 is one per pixel. Think of it this way:
    4:4:x means every 4 horizontal luminance pixels you get four chroma pixels (Cr, Cb, Cr, Cb)
    4:4:4 means you get different samples for each chroma value on the scan line below (i.e. another set of Cr, Cb, Cr, Cb).

    4:2:x means in a set of 4 luminance pixels the first two pixels have a Cr and the second two a Cb
    4:2:0 means the next line uses the luminance pixels from the line above and no has no more chrominance information.

    So if we do a 2x2 scaling on the luminance pixels but keep all the chrominance pixels then over each two lines of 4 pixels (made from 8 lines of 4) we get an output pixel with alternating Cr, Cb values for every line, which is 4:4:4.

    E.g. scaling 8x4 to 4x2

    4:4:4 -

    Cr Cb Cr Cb Cr Cb Cr Cb
    Cr Cb Cr Cb Cr Cb Cr Cb
    Cr Cb Cr Cb Cr Cb Cr Cb
    Cr Cb Cr Cb Cr Cb Cr Cb

    4:2:0

    Cr -- Cb -- Cr -- Cb --
    -- -- -- -- -- -- -- --
    Cr -- Cb -- Cr -- Cb --
    -- -- -- -- -- -- -- --

    4:4:4 native at half H and V resolution -

    Cr Cb Cr Cb
    Cr Cb Cr Cb

    (Note if scaled higher res to get here would have multiple chrominance samples per output sample)

    4:2:0 scaled by 2 in H and V -

    Cr Cb Cr Cb
    Cr Cb Cr Cb

    (Note each chrominance sample is just copied from the higher res image.)

    Sorry for issues due to the font, may be clearer cut and pasted into Notepad or similar."
     
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