Originally Posted by Bob Pariseau
Zuter, I think you ran into the trap of trying to calibrate mismatched RGB settings. If one side of the cable is using one choice (RGB Video Level vs. RGB PC Level) but the other side is expecting the opposite choice, those are mismatched settings. The HDMI handshake -- and any sort of "Auto" setting at either end -- can NOT correct such a mismatch. It is something that has to be set Manually -- at both ends of the cable -- unless you luck out and find the default settings choice at each end just happens to match.
Now, if you have a settings mismatch, you can APPROXIMATE calibrating you system by adjusting the video levels to "correct" the mismatch. For example, if the player is sending RGB Video Level (Black=16) whereas the Kuro is expecting RGB PC Level (Black=0) you can approximate proper calibration by lowering black levels (Brightness setting) in the Kuro. I.e., at a given setting of Brightness, the RGB Video Level input signal will appear 16 steps brighter than the RGB PC Level signal, but if you "correct" that by lowering the Brightness setting in the Kuro you will still get Black portions of the content looking "black" on the display. A similar sort of mistaken adjustment fixes the mismatch at the high Luma (White) end of the signal -- in that case it is the Contrast setting in the Kuro.
But this sort of "correction" is not, umm, correct! You are expanding or squeezing the data range between Black and White which means you will get artifacts such as banding.
So you have to START by getting both sides of the cable set to use the same flavor of RGB, and only THEN can you calibrate your levels (e.g., Brightness & Contrast).
Now, the data on shiny discs, and also on TV broadcasts, is YCbCr. The encoding scheme for YCbCr matches what you get with RGB Video Level -- i.e., black = 16. The full data range of Luma (i.e., the data range representing gray scale from Blackest to Whitest) in either RGB Video Level or YCbCr works like this:
Luma 0-15 <-- the "Blacker than Black" values
Luma 16 <-- Reference Black
Lume 235 <-- Reference White
Lume 236-255 <-- the "Peak White" values
The Blacker than Black and Peak White values provide headroom at either end so that video processing doesn't hit a hard wall, which can cause artifacts.
RGB PC Level on the other hand works like this:
Luma 0 <-- Reference Black
Luma 255 <-- Reference White
There are no values below 0 or above 255 so there's no place to carry the Blacker than Black values or the Peak White values. There are more STEPS between Reference Black and White for RGB PC Level, so it allows for a finer step size for each step, but there's no place to carry the below black or above white values during processing. RGB PC Level is designed for use by Computer Graphics cards talking directly to Computer Monitors. The graphics are created on-the-fly in the card, and there's no processing after that. So the finer step size is good, and the lack of headroom at either end is not a problem. So, for example, games machines like to use RGB PC Level. The PS3 is designed to use RGB PC Level when playing games, and the games are authored expecting that. (Indeed the PS3 doesn't even offer a proper implementation of RGB Video Level -- but no problem because you can set it to automatically switch to YCbCr output when playing movies.)
But use of RGB PC Level for movie or TV content is *NOT* a good thing. That content was created expecting the Video Level step sizes. By introducing more steps between Black and White you introduce rounding errors. And, again, the Blacker than Black and Peak White data ranges have to be discarded. There's no place for them in RGB PC Level.
The Kuro displays have a reputation of working better with RGB data format than with YCbCr. But ideally that should be RGB Video Level data format, and not RGB PC Level.
I suspect what's going on in your setup is that your Kuro is set to expect RGB PC Level whenever it sees RGB data format on the HDMI input cable. As such, setting the player to RGB PC Level lets you get a good image once the video levels in the Kuro (e.g., Brightness & Contrast) are calibrated correctly. However, that may not be the "best" image!
If you change to RGB Video Level in *JUST* the player, then you will find that you need to change the Brightness/Contrast settings in the Kuro to get correct Black and White levels. But that's a bandaid -- the wrong way to do it. And will likely result in a poorer quality image.
What you need to do instead is find the companion setting in the Kuro that ALSO changes the KURO to expect RGB Video Level. If you do that -- that is if you change BOTH the player and the Kuro to use RGB Video Level data format -- then you should find that NO CHANGE (or only minor change) is needed in the Brightness and Contrast settings which worked before when you were using RGB PC Level. And what's more, the resulting image should look better when playing movies because you are now using Luma step sizes which match the way the data was actually authored on disc.
With both the player and the Kuro set to use RGB Video Level -- and again, these are settings choices you have to set Manually -- then correct calibration will have Luma values of 16 and below all merged into a single, indistinguishable "Black". That is, the Blacker than Black steps of Luma should not be visible. Luma 16 -- Reference Black -- and the steps below it should ALL produce the blackest pixel output your display can produce, which on the Kuro is pretty darned BLACK!
Those Blacker than Black values still participate in video processing, so you don't want to just discard them! But the end result, AFTER all the processing, is that all pixels which are Black or below should produce a single, undifferentiated "black" output on the display.
At the other end, proper calibration depends on the dynamic range of your display. The starting point is that Luma values up to Reference White should all be distinguishable. If you can't distinguish between Luma steps from say 230-235 then you will have to lower Contrast to eliminate that crush of Whites. This lowers the light output of the display. But what of the Peak White values? Well if you keep lowering Contrast you should be able to distinguish the steps even ABOVE Reference White. Ideally you should be able to distinguish all the way up to Luma 254 (against a 255 background). But your display may not have enough Contrast range to do that. Or if it does, you may not like the amount of light output the display produces for Reference White. I.e., a patch of Reference White (Luma 235) may not appear "white" enough to please you.
If you raise Contast so that the highest Luma step you can distinguish is Reference White, then you will also be increasing the light output of Reference White -- but you will not be able to distinguish glints, sparks, cloud highlights, etc., which are on disc using pixel values in the Peak White range. So depending on the light output of your display, your preference for Room Lighting while watching, and the range of Contrast adjustment available, you may be able to get pleasing results with ALL the Peak White range visible, or just a portion of it, or none of it. So long as you don't crush values below Reference White you are OK, but if you can keep from crushing Peak Whites you are even better.
Again, using RGB PC Level, none of this comes to bear, because you have DISCARDED all the Peak White values by the choice of RGB PC Level data format.
To check this, I recommend you use the Spears & Munsil, Blu-ray, calibration disc. The Dynamic Range Low chart puts up flashing bars either side of Reference Black with the bars labeled in individual Luma steps. You can check EXACTLY what you can distinguish near Reference Black. Similarly the Dynamic Range High chart puts up flashing bars from just below Reference White all the way up to Luma 254 (against a Luma 255 background). So you can check EXACTLY what's distinguishable up there.
As a final check, the Clipping chart shows exactly what is going on with White, Red, Green, and Blue for the highest Luma values. So you can make sure all 3 colors are getting through without Crush at your choice of Contrast setting. I.e., if you see one color is still getting Crushed, then that could be an indication you need to lower Contrast further.
(A professional calibrator will also use light sensor tools to make sure the light output of Reference White is adequate, and to double-check that the video level processing in the Kuro is doing the right thing for gray scale and the colors -- making adjustments as necessary to produce the best compromise solution, which in the Kuro shouldn't involve much of anything in the way of compromise!)
Hope this helps!