November 28, 2015 at 10:50PM

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You voted '+1'.

Is 4k in 4:4:4 actually 16k?

Okay so I've been doing some studying on the real science behind chroma sub sampling (http://www.5dfilmmaking.com/tut_444.htm), and I realized that 1920x1080 at 4:2:0 sampling is essentially taking every 4x2 set of pixels, so 8 and turning them into two pixels right? well if so does that mean that you're effectively taking a 1920 image and reducing it to 480 then scaling it back up again? I must be misunderstanding something or is that how it works. Or is 4k at 4:4:4 showing 4 times the quality? Now I'm all confused! Help please!

6 Comments

The 4K represents gray-scale brightness information ( or video signal luma ), while the second group of numbers represent the color information ( or video signal chroma ).

Here's a handy video signal chart that illustrates what happens to the color information when it's sub-sampled to different color-spaces in order to compress the amount of color information stored in the video signal.

https://goo.gl/uDMfA6

So as you can see, 4:4:4 color space does not compress the color information for each pixel in the video image, it does NOT increase the resolution of the grey-scale luma information ( it's still 4K resolution ), but it accurately stores a unique piece of color information for each pixel in the video image. Looking at this chart it's amazing that this form of compression works for lower resolution color spaces like 4:2:0.

November 28, 2015 at 11:28PM, Edited November 28, 11:30PM

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Guy McLoughlin
Video Producer
31013

Chroma subsampling:
4K 3840x2160 4:2:0 video has only 1920x1080 color resolution.
4K 3840x2160 4:2:2 video has only 1920x2160 color resolution.
4K 3840x2160 4:4:4 video has full 3840x2160 color resolution.
-> 4K 4:2:0 = 2K 4:4:4
-> 8K 4:2:0 = 4K 4:4:4
-> 16K 4:2:0 = 8K 4:4:4

Bayer sensor:
4K 3840x2160 4:4:4 monitor has Red:3840x2160, Green:3840x2160, Blue:3840x2160 color resolution.
4K 3840x2160 4:4:4 camera has 50% green, 25% red and 25% blue color pattern.
-> To get "true" 4K 4:4:4 video, you have to have 16K 133Mpix! bayer sensor camera?

Edit: Massive editing.

November 30, 2015 at 3:21PM, Edited November 30, 4:19PM

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ƃɹǝqoɹT ɐʞʞnnT
ɹǝɥdɐɹboǝpıʌ
98

Okay that cleared up my question thank you. But man those numbers are ridiculous. So for the past 3 years I've been shooting 1920x1080 at 4:2:0 which means everything has been 480p color resolution... that's depressing.

Clark McCauley

December 1, 2015 at 11:58AM

-> It seems that 8K 33Mpix for 4K 4:4:4 is enough. http://imgur.com/F8Thxlx.png

November 30, 2015 at 4:36PM, Edited November 30, 4:37PM

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ƃɹǝqoɹT ɐʞʞnnT
ɹǝɥdɐɹboǝpıʌ
98

4K is 4K no matter the subsampling.
Even in 4:2:0 you have true 4K luminance samples. In 4:4:4 you don't gain more resolution, you gain more color fidelity.

December 2, 2015 at 7:21AM

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Ezi Seel
615

One book I can't recommend enough is The Filmmaker's guide to diital imagry. If you really want to get into the nitty gritty of what happens in your digital camera, then that is the book you want. Or google 'books to become a DIT (Digital Imagry Technician)' to see all the options.

December 3, 2015 at 2:37PM

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