Originally Posted by millerwill
My wife's out of town this weekend, so it's a good time to play a bit with calibration,etc. Here below are some results I've measured fairly carefully (light meter on a tripod, so no variation with position,etc.) that are related to 'setting contrast', a topic that has been under active discussion in the 'Setting Contrast with the Munsil&spears calibration disc ...' in the Display Calibration thread.
I use 'Expanded' HDMI mode (as recommended by Greg Rogers, and a number of others), am in Normal (i.e., low) lamp, with Iris at 0 (fully open). Brightness is set to -5; this is unambiguous, coming out to this value from a variety of calibration discs (M&S, GetGray, AVSHD709, DVE BluRay, AVIA, etc.) as do a number of others.
The question comes with setting Contrast. If I set it as M&S recommend, to show the 'white bars' all the way up to ~251 (i.e., the WTW region), then Cst comes out to +6 (as other respected pro's--e.g., ChrisWiggles--also find). OTOH, if one sets Cst to show only the region up to 235 ('reference white'), as the highly respected GetGray disc recommends, I come up with Cst = +13 or +14. The discussion over in the calibration thread is whether or not there is any 'useful video info' in the WTW region, or whether setting Cst to show WTW gives less 'ringing' (or other artifacts) in the 'allowed' region (</= 235). So the possible range I have to choose for Cst is from +6 (showing all the WTW region) to +14 (showing none of it).
What I have measured is the effect this range of Cst has on the lumen output of my RS20. A higher Cst setting gives more lumens, so other things being equal would be preferred, unless lower Cst has some pq advantages. Here are the measurements:
Contrast Lumens ftL Ratio
+6 287 14.6 1.00
+8 300 15.3 1.05
+10 314 16.0 1.09
+12 327 16.7 1.14
+14 341 17.4 1.19
(The ftL #'s assume a screen gain of 2.4 for my 126" diag 16x9 HP screen.) The ratio is taken relative to the Cst = +6 value.
So going to the max Cst, i.e., eliminating all WTW, gives ~19% more brightness (lumens), and one sees very linear behavior over this region. If one is 'ftL poor', then one may very well wish to use these higher Cst settings. It will also be extremely useful to see if the 'Setting Contrast' thread comes to any conclusion about the advantages, or not, of covering the WTW region. (Again, there are very knowledgeable persons who seem to come down on opposite sides of this question.)
I would be interested hearing what value others of you choose for setting Cst (assuming that you use 'Expanded' HDMI mode).
Thanks for the report. I run with HDMI type Normal. I keep contrast and brightness both at 0. Technically speaking for my setup brightness should be at 1 and contrast at -1 or -2.
I use brightness at 0, however, because just a single click significantly raises the absolute black level significantly. So I am willing to trade a little bit of black crush (notably I cannot really see bar 17 with brightness at 0) for inky blacks.
Contrast at 0 for me makes the 234 bar barely visible. It is more defined at contrast -1 and a bit more so at -2. However I have not found material yet with very bright whites where I could notice a difference between -2, -1 and 0, so I keep it at 0 to maximize brightness and CR.
As far as Enhanced HDMI goes, I do not run it because I have no interest in running BTB or WTW. This is a personal decision. The purists out there have good reason to want to have WTW because as I understand it there is sometimes material in the 235+ range that if not calibrated for will result in some white crush.
However, from what I understand such scenes are very rare, and may only be on particular films. It sounds like we are talking about a very rare occurrence and that when it happens it may even go unnoticed to the trained eye (i.e. not stick out like a sore thumb).
To me personally I would much rather run calibrated up to 235 and pick up all this extra brightness and on/off CR, then to be calibrated for all scenarios, when such scenarios (235+) are rare. Again this is a personal taste type of thing so YMMV.
As an experiment I did try running in Enhanced mode with things set to clip at BTB and WTW. The settings for this were contrast at 15 and brightness at -7. Such settings produced identical results to running in Normal mode with contrast/brightness at 0 with various material I tested. For reference, in my case contrast of 13 with brightness of -6 in Enhanced mode was equivalent to contrast of -2, brightness of 1 in Normal mode.
millerwill - I highly encourage you to ensure that you really need brightness at -5. That seems a bit high to me. Forget about your contrast-setting patterns for now and try this experiment...
With brightness at -5, put up a 0% pattern (full field/screen absolute black). Bring up the Brightness control and click on it so the slider is shown on the bottom of the screen and rest of the RS20 menu is hidden. Now watch the overall black level on the screen and reduce the slider to -6. Notice how much the blacks go down? It should be significant if your set up is like mine. Now bright it down one click again to -7. You should notice the same dropoff and you are now at inky blacks (comparatively). You will also notice that if you try to go any lower the black level will remain constant.
This experiment has real world implications because your lowest black levels at -5 will look that much brightness in your scenes (especially very dark ones) compared to the -7. My guess is that by running at -5 you are running with a on/off CR about 30% lower than it would be with -7. Of course there are trade offs because with -7 you will have slight black crush. But to me this is a worthwhile trade off.
Lastly, all this assumes that your projector is calibrated near perfectly including extensive gamma tweaking aka leDahu's spreadsheet so that the 5% (and all other levels) are dialed in correctly.