petetherock Posted May 29, 2018 Share Posted May 29, 2018 As we move into 4k, this is very useful: http://www.personal-view.com/talks/discussion/6144/easy-video-explaining-444-422-and-420-for-noobs/p1 [embed=425,349] [/embed] Link to comment Share on other sites More sharing options...
petetherock Posted May 29, 2018 Author Share Posted May 29, 2018 https://www.rtings.com/tv/learn/chroma-subsampling What is Chroma Subsampling? Chroma subsampling is a type of compression that reduces the color information in a signal in favor of luminance data. This reduces bandwidth without significantly affecting picture quality. A video signal is split into two different aspects: luminance information and color information. Luminance, or luma for short, defines most of the picture since contrast is what forms the shapes that you see on the screen. For example, a black and white image will not look less detailed than a color picture. Color information, chrominance or simply chroma is important as well but has less visual impact. What chroma subsampling does is reduce the amount of color information in the signal to allow more luminance data instead. This allows you to maintain picture clarity while effectively reducing the file size up to 50%. In the YUV format, luma is only 1/3rd of the signal, so reducing the amount of chroma data helps a lot. Because of bandwidth limitations from internet speeds and HDMI, this makes for much more efficient use of current systems. 4:4:4 VS 4:2:2 VS 4:2:0 The first number (in this case 4), refers to the size of the sample. The two following numbers both refer to chroma. They are both relative to the first number and define the horizontal and vertical sampling respectively. A signal with chroma 4:4:4 has no compression (so it is not subsampled) and transports both luminance and color data entirely. In a four by two array of pixels, 4:2:2 has half the chroma of 4:4:4, and 4:2:0 has a quarter of the color information available. The 4:2:2 signal will have half the sampling rate horizontally, but will maintain full sampling vertically. 4:2:0, on the other hand, will only sample colors out of half the pixels on the first row and ignores the second row of the sample completely. Link to comment Share on other sites More sharing options...
desray Posted June 1, 2018 Share Posted June 1, 2018 https://www.rtings.com/tv/learn/chroma-subsampling What is Chroma Subsampling? Chroma subsampling is a type of compression that reduces the color information in a signal in favor of luminance data. This reduces bandwidth without significantly affecting picture quality. A video signal is split into two different aspects: luminance information and color information. Luminance, or luma for short, defines most of the picture since contrast is what forms the shapes that you see on the screen. For example, a black and white image will not look less detailed than a color picture. Color information, chrominance or simply chroma is important as well but has less visual impact. What chroma subsampling does is reduce the amount of color information in the signal to allow more luminance data instead. This allows you to maintain picture clarity while effectively reducing the file size up to 50%. In the YUV format, luma is only 1/3rd of the signal, so reducing the amount of chroma data helps a lot. Because of bandwidth limitations from internet speeds and HDMI, this makes for much more efficient use of current systems. 4:4:4 VS 4:2:2 VS 4:2:0 The first number (in this case 4), refers to the size of the sample. The two following numbers both refer to chroma. They are both relative to the first number and define the horizontal and vertical sampling respectively. A signal with chroma 4:4:4 has no compression (so it is not subsampled) and transports both luminance and color data entirely. In a four by two array of pixels, 4:2:2 has half the chroma of 4:4:4, and 4:2:0 has a quarter of the color information available. The 4:2:2 signal will have half the sampling rate horizontally, but will maintain full sampling vertically. 4:2:0, on the other hand, will only sample colors out of half the pixels on the first row and ignores the second row of the sample completely. Everyone... Understanding the underlying concept is important but knowing how it will affect the overall PQ on your display if you choose one over the other two is even more important... U urge everyone to start playing with this chroma sub sampling to better appreciate the effects it will have on your TV and projector. Don't just read the theory, practical and hands-on experience to see the differences is way more important than regurgitating technical facts... Hint: if your TV or projector on board video scaler is good, u will not see much difference but it will prevent intermittent signal blackout due to the bandwidth allocation. For those using TV as your second display monitor (which I do not encourage), this chroma sub sampling will have a bigger impact on the legibility of your text and true type fonts. Sent from my Vivo X21 UD Link to comment Share on other sites More sharing options...
wacko Posted June 1, 2018 Share Posted June 1, 2018 question, does this matter when video sources such as DVDs and Blu-rays are almost entirely (if not all) in 4:2:0 chroma? Link to comment Share on other sites More sharing options...
desray Posted June 1, 2018 Share Posted June 1, 2018 question, does this matter when video sources such as DVDs and Blu-rays are almost entirely (if not all) in 4:2:0 chroma? No. For video sources like movies authored in bluray (don't talk about DVD these days) and UHD 4K bluray, it is all authored in 4:2:0 8bit and up to 10bit natively. The effects of chroma sub sampling is not really an issue here as long as you have a good display or source to do the conversion....in fact, most of the conventional 4K UHD TV these days have no issue with it. Rule of thumb, it is better to do source direct for your bluray/4K UHD bluray player and allow the display to do the conversion from 4:2:0 to 4:4:4 instead of the other way round. Link to comment Share on other sites More sharing options...
keai Posted June 1, 2018 Share Posted June 1, 2018 nice video, help to understand easily. thanks Pete! Bro desray, mind to elaborate how displays or players able to convert 4:2:0 to 4:4:4 if source is at 4:2:0? Sorry if this is a stupid question but I can't paint the picture how 4:4:4 can be converted from 4:2:0 source correctly. Link to comment Share on other sites More sharing options...
desray Posted June 2, 2018 Share Posted June 2, 2018 nice video, help to understand easily. thanks Pete! Bro desray, mind to elaborate how displays or players able to convert 4:2:0 to 4:4:4 if source is at 4:2:0? Sorry if this is a stupid question but I can't paint the picture how 4:4:4 can be converted from 4:2:0 source correctly. Bro keai, just remember this easy concept of chroma sub-sampling...the end-game (or goal) is to get 4:4:4 (RGB)...using YUV which is less bandwidth-hogging, the baseline starts with 4:2:0 or 4:2:2 in order for the signal to send to the display with less anomalies like intermittent signal loss etc. You can either choose to send a un-sampled chroma (4:4:4) assuming your source (bluray player) is able to decode and then pipe it over to the display but this may not be ideal for people running longer HDMI cable. Link to comment Share on other sites More sharing options...
keai Posted June 2, 2018 Share Posted June 2, 2018 Bro keai, just remember this easy concept of chroma sub-sampling...the end-game (or goal) is to get 4:4:4 (RGB)...using YUV which is less bandwidth-hogging, the baseline starts with 4:2:0 or 4:2:2 in order for the signal to send to the display with less anomalies like intermittent signal loss etc. You can either choose to send a un-sampled chroma (4:4:4) assuming your source (bluray player) is able to decode and then pipe it over to the display but this may not be ideal for people running longer HDMI cable. Dont quite get it, the signal transmit portion is understandable, just dont quite understand how 4:2:0 source signal can be upgraded to 4:4:4. Sent from my SM-G935F using Tapatalk Link to comment Share on other sites More sharing options...
desray Posted June 2, 2018 Share Posted June 2, 2018 It's done internally by the on board video scaler in your display. We dun need to know that... Just need to know that there will be conversion... Just like u take a train, you dun need to know how the parts and components work to make the train move... LoL Dont quite get it, the signal transmit portion is understandable, just dont quite understand how 4:2:0 source signal can be upgraded to 4:4:4. Sent from my SM-G935F using Tapatalk Sent from my Pixel 2 XL using Tapatalk Link to comment Share on other sites More sharing options...
keai Posted June 2, 2018 Share Posted June 2, 2018 maybe i didnt get my question clear. correct me if my understanding is off: 4:4:4 is like lossless music format, for instance wav or flac, 4:2:0 is like mp3, to convert 4:4:4 to 4:2:0 is possible for sure, like a wav or flac file being compressed to mp3 with losses of details. however, it is not able to convert a mp3 file back to flac pr wav file to be exactly the same as the original wav or flac, as the missing piece is gone. if apply the same logic to bluray/UHD bluray, source is already 4:2:0, like mp3, no matter how capable the player/display is, it cant accurately upgrade 4:2:0 to 4:4:4 theoretically, or I misunderstand the concept here? Sent from my SM-G935F using Tapatalk Link to comment Share on other sites More sharing options...
desray Posted June 2, 2018 Share Posted June 2, 2018 maybe i didnt get my question clear. correct me if my understanding is off: 4:4:4 is like lossless music format, for instance wav or flac, 4:2:0 is like mp3, to convert 4:4:4 to 4:2:0 is possible for sure, like a wav or flac file being compressed to mp3 with losses of details. however, it is not able to convert a mp3 file back to flac pr wav file to be exactly the same as the original wav or flac, as the missing piece is gone. if apply the same logic to bluray/UHD bluray, source is already 4:2:0, like mp3, no matter how capable the player/display is, it cant accurately upgrade 4:2:0 to 4:4:4 theoretically, or I misunderstand the concept here? Sent from my SM-G935F using Tapatalk Bro Keai, great analogy you got there for this. You are NOT WRONG to say that 4:2:0 (YUV/YCrCb) up-sample the chroma to 4:4:4 (RGB) will never achieve a FULL 4:4:4 (lossless format) since the source itself is already in a "lossy" format - i.e. 4:2:0 to begin with...The concept here is 4:2:o/4:2:2 and 4:4:4 has minimal visual perceptivity in terms of the picture quality. This is true for normal bluray title which is mastered in 4:2:0 at 8-bit color but for HDR content, it is authored in 4:2:0 at 10-bit or more (12-bit for Dolby Vision). In order for a wider color gamut to be shown so as to increase the dynamic range of the colors from say a Rec 709 colors to at least a BT2020 (HDR), chroma sub-sampling to a 4:4:4 (RGB) is a must so as to create the "extra" colors...now the question is WHETHER OR NOT, the up-sampling of "lossy" (4:2:0) will accurately captured a full range (4:4:4), that will very much depends on how well ithe video processor of the source (4K UHD player, AVR on board video scaler or Graphics Card on a HTPC) or the display (OLED TV or Projector/Monitor) can assimilate the sub-pixels (e.g. bi-cubic or nearest bilinear concept apply on a software based media player) using their very own proprietary video chipset (recall VXP, Faroudja DCDi etc) to do their own micro-computing algorithms to "best-guesstimate" each individual sub-pixels (akin to BFI or Black Frame Insertion in a video processing) to get a better and superior PQ overall on the display. Our human eyes are more susceptible to Brightness (Luminance) than colors (Chroma), hence most of the movies are authored in 4:2:0 at either 8-bit (SDR) or 10/12bit (HDR) since we can only see up to certain range of colors before the luminance (brightness of the colors) takes over. Hence it makes perfect sense for 4:2:0 compression to make its way to our physical disc media to save the precious disc space. Let's say we are talking about using the source for chroma sub-sampling (4K bluray player), you are not wrong to say that 4:2:0 up-sampling to 4:4:4 will not confirm to produce superior PQ on the display because it depends very much on the player itself - that is why Oppo players with a more superior chipset may provide better chroma sub-sampling conversion from 4:2:0 to 4:4:4 as compared to say a China-made 4K bluray player. Rule of thumb is to allow display - i.e. your OLED TV or Projector to do the final 4:4:4 conversion as opposed to allowing the player to do that for you...YMMV. Link to comment Share on other sites More sharing options...
desray Posted June 2, 2018 Share Posted June 2, 2018 Actually let me sum up in the most simplest way...4:2:0 (lossy video luminance/chroma) is an "intentional" decision made by film industry when they authored normal bluray and 4K UHD bluray so as to ensure that the movies (w/o suffering from much PQ deterioration) can be burned to the disc medium and at the same time allow any sub-par 4K UHD bluray player or less-than-superior (inferior quality) HDMI cable to transmit the video signal with as little hiccups to the displayer as possible. Bottom line is, you will need a good displayer like your TV or Projector to really make the 4K movies SHINE! Link to comment Share on other sites More sharing options...
keai Posted June 2, 2018 Share Posted June 2, 2018 thanks bro desray, for the detailed elaboration, it helps a lot to better understand the whole PQ and chroma thing! Sent from my SM-G935F using Tapatalk Link to comment Share on other sites More sharing options...
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