What Is Color Encoding? - AVS Forum
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post #1 of 15 Old 01-02-2013, 10:27 AM - Thread Starter
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While reading up on a new TV I have recently bought, I came across this while doing some "investigating" on the PC Labeling option on the Samsung. I apparently found out that the reason the PC Mode locks out the Color, Tint, or 10p White balance options, is because RGB doesn't need any Color encoding.

So, my question is, what is Color encoding?

To the best of my knowledge, you need one because movies are in YCBCR, and with it being a way of encoding RGB, it needs calibrating properly. A little like properly unwrapping YCBCR to RGB? well, that's my amateur go at it anyway smile.gif

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post #2 of 15 Old 01-02-2013, 11:47 AM
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It's talking about the difference between YCC and RGB.

RGB is encoded into YCC, then YCC needs to be decoded into RGB.

Color and tint controls in general are a by product of how Color TV was introduced as an add-on to B&W TV.

It used to be in the olden days that everything was just Y.
When they added color they did it by introducing YCC where the color information was differenced from the luminance data. Not only that but the color imformation was broadcast on slightly different radio frequencies (remember in olden days all TV came over the air). The issue being now at 25-50 miles out from the broadcast the slightly different frequencies would have different attenuation and could even be shifted somewhat in phase.

So the Color control is intended to return the amplitude of the color signal to the correct amount. The Tint (or phase) control is there to correctly align the color signal with the Y information.

So these are input values on the Color Decoder algorithm (built as an analog circuit in the olden days) that take the YCC information and turn it into RGB output (IRE voltages in the olden days) that the display can actually use to fire up it's red, green and blue pixels.


When you feed a TV RGB directly, color and tint aren't necessary because there was no encoding to begin with, the RGB values provided are already correct. Any further calibration necessary should be done with the CMS controls that already work in the RGB space.

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post #3 of 15 Old 01-02-2013, 02:22 PM - Thread Starter
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Ok thanks again.

Now I'm obviously asking this because of video games which I'll use my display for a lot. I read on here in a thread that someone started that video games use sRGB which is the REC 709 of course, what would happen there then. Would it still not need any Color decoding?

I'm not 100% sure that all game developers use sRGB, but as the guys said on that thread, it's the best you can calibrate too for games.

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post #4 of 15 Old 01-02-2013, 04:28 PM
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RGB data has not been encoded, so their is no decoder.

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post #5 of 15 Old 01-02-2013, 05:49 PM - Thread Starter
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Quote:
Originally Posted by sotti View Post

RGB data has not been encoded, so their is no decoder.
so by that do you mean it doesn't matter if it's sRGB or Adobe RGB?

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post #6 of 15 Old 01-02-2013, 09:44 PM
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Quote:
Originally Posted by Tyrone Burton View Post

so by that do you mean it doesn't matter if it's sRGB or Adobe RGB?[/quote

RGB isn't encoded, the only way you determine the output is by the calibration of the display.

RGB says green is 0,255,0 if that's sRGB then green has the x,y value of 0.30,0.60. If that green is for Adobe RGB then it's still 0,255,0 but the x,y is 0.21, 0.71. But the x,y values are set on the calibration of the display.


In PC world you run your monitor in native gamut (As big as it can get), then you describe the monitor to the computer via ICC, then anything that is color-managed (photoshop, illustrator, apps like that) can use ICC profiles that get tagged into images to know how that content should be displayed.

But 90% of content on a computer doesn't have ICC profiles, games and video players don't use ICC, so they all run in native gamut, but are typically designed for sRGB.

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post #7 of 15 Old 01-02-2013, 10:04 PM - Thread Starter
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I meant. If my PC mode doesn't need any Color or tint controls because it takes RGB strait from the source, then what about sRGB? it's the REC 709, doesn't it still need it's Color calibrating?

Or doesn't that matter, will I still get the correct Color? Of course I set the contrast a black level first.

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post #8 of 15 Old 01-02-2013, 10:53 PM
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The reason is that Tint and Color are YCbCr controls.

Anything described in R,G,B doesn't need a color decoder because Magenta is just R+B, Yellow is R+G and Cyan is B+G. Those tint shades are already calculated for the display because it's described in the displays native colors. When you move to YCC, everything is described relative to RGB primaries via a color matrix, in order to convert the YCC data into the correct RGB levels you have to have advance knowledge of what that matrix should be for the content.

This is where the rec.601 v rec.709 thing comes in, when converting the RGB data into YCC data it uses the primary RGB data to build the matrix to try and maximize the useable YCC codes.

Just for reference:
Red RGB: 255,0,0
Red YCrCb:54, 256, 99

Green RGB: 0,255,0
Green YCrCb: 182,12,30

Blue RGB: 0,0,255,0
Blue YCrCb: 18,116,256

White RGB: 255,255,255
White YCrCb: 255,128,128


So you can see the R + G+ B = white.
This is actually the same for YCC as well, the Y's add up to 255, when you look at the Cb,Cr data it's actually +- data centered on 128 (A Cb value of 99 is actually a -29). When you account for that, the Cb and Cr values both actually total 128, 128. The part where you can see how the rec.709 standard comes in is that Y is the luminance information, Red is 21%, Green is 71% and Blue is 8% of the Y, because those are the exact Y values for rec.709. And those Y values are derived from the x,y chromaticity of the Primaries that add up to D65.

But matrix and the match to convert that YCbCr data into R,G,B data that the monitor understands. So the tint and color control tweak the standard matrix to either exaggerate or minimize the CbCr difference to decrease color luminance, or twist the CbCr values so that the output is more Red or Green or Blue.

Even know if a something does process RGB to apply tint or color, they first convert it into YCC then back to RGB.

Regardless, you don't need color and tint anyway. RGB data is already correct, and if your YCC decoder is funky your color and tint controls won't fix it. More often YCC decoders work correctly in movie mode, so they are also correct at default.

Bottom line, calibrate to rec.709 and don't worry about it.

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post #9 of 15 Old 01-02-2013, 11:30 PM - Thread Starter
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Ok thanks for that long write there. You know your stuff buddy smile.gif

maybe I'll have to give that another read forgive me, but by the sounds of it your saying yes, it doesn't matter if it's sRGB.

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post #10 of 15 Old 01-02-2013, 11:38 PM
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I wouldn't worry too much about calibrating for gaming as I've heard that not many game developers actually produce the games in a colour controlled environment anyway.
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post #11 of 15 Old 01-03-2013, 02:39 PM
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Then there is the complication that many TVs do NOT lockout Color and Tint (or any other controls) for RGB inputs... in those cases, the TV is converting RGB to YCbCr for processing in the TV. When that is done, all the controls are still available. So just because you send an RGB signal to a TV doesn't mean the controls will be unavailable... they might be unavailable or they might still work fine. Much of the time you don't tweak Color or Tint anyway (in digital video) so it's not something worth obsessing over.

And... some TVs look better when you send YCbCr versus RGB or vice versa. So even though the TV may be able to accept RGB fine (every TV I've seen in the last 5 years does), the TV might actually look better when you send YCbCr or not... RGB might look a little better than YCbCr. Or both RGB and YCbCr might look the same. You can't know this in advance unless someone who reviewed the TV spent time looking into that particular parameter and reported it in the review.

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post #12 of 15 Old 01-03-2013, 02:56 PM - Thread Starter
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Well i think I'll keep using my PC mode for all games, seeing as the signal will be RGB and the Color controls are locked, I'm getting the correct Color even if games dont keep to any standard.

Thanks for clearing that last bit up Doug. I now know that if the signal I'm sending to the TV is RGB, but I'm still seeing all the controls, it must mean the TV is converting to YCBCR for display.

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post #13 of 15 Old 01-03-2013, 03:48 PM
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Quote:
Originally Posted by Tyrone Burton View Post

it must mean the TV is converting to YCBCR for display.

For processing.

Displays can only display RGB, since their is no such thing as a Cb pixel.

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post #14 of 15 Old 01-03-2013, 09:17 PM
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Any Info on rgb yc is appreciated.
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post #15 of 15 Old 01-03-2013, 09:39 PM
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Quote:
Originally Posted by Vic12345 View Post

Any Info on rgb yc is appreciated.
This is a bit of information on YCbCr:
http://www.dvd-replica.com/DVD/color.php

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