I took the time to explore various 45 modes and controls regarding the recent conversation. I used a Playstation3 and the Disney WOW disc.
Here are my results.
DR = dynamic range
PS3 DR setting is only available in PS3 RGB mode.
Note the 45 may display full or limited actual contrast range depending on setting. When displaying full contrast range, black is blackest black, white is whitest white the 45 can produce. When displaying limited contrast range, data black is elevated from blackest black, white is reduced from whitest white, resulting in a bland picture.
Here is a summary of permutations of PS3 and 45 dynamic range modes.
PS3 RGB Full mode
45 DR setting makes no difference: full contrast range of 45 is displayed, btb/wtw are clipped
PS3 RGB Limited mode
45 DR setting makes a difference:
45 DR auto displays full contrast range of 45, btb/wtw are clipped
45 DR limited displays full contrast range of 45, btb/wtw are clipped
45 DR full displays limited contrast range of 45, btb/wtw are clipped
PS3 Superwhite is only available in PS3 Ycbcr mode. PS3 Superwhite is equivalent to PS3 RGB dynamic range full: btb and wtw are passed from the disc but whether they are displayed depends on the 45 mode.
PS3 Ycbcr mode
45 DR setting makes a difference
45 DR auto shows full contrast range of 45, btb/wtw are clipped, Superwhite makes no difference
45 DR limited shows full contrast range of 45, btb/wtw are clipped, Superwhite makes no difference
45 DR Full shows full contrast range of 45, Superwhite makes a difference:
• Superwhite off: 45 displays limited contrast range and btb/wtw are clipped
• Superwhite on: 45 displays full contrast range and btb/wtw are revealed
Note that while the WOW test patterns with btb/wtw data are affected, the 3 WOW example images, model, dock-sea, market-crates are affected by 45 DR but are not affected by PS3 Superwhite, as these contain no btb/wtw data. Same with all movie clips.
Based on my results I cannot see how Superwhite can be used, because it only works if the 45 is in Ycbcr mode, which harms 45 displayed contrast range when 45 is in limited mode and it can only reveal data not present in consumer encodings when 45 is in full range mode. Maybe it involves a flag that mysteriously comes into play for some content when the 45 DR is in auto mode? But why? Would love if anyone can explain this.
Sony 45 has a Clearwhite mode of Off/Low/High. When the PS3 Superwhite is enabled (Ycbcr) and the 45 DR is set to auto or limited, Clearwhite Low enables 0% wtw star and Clearwhite high enables the +1% wtw star. Both are missing red, either by design, or because the 45 red channel is clipping. Clearwhite also affects peak white balance by making it slightly cooler. Again, like PS3 Superwhite I cannot see how or why 45 Clearwhite should be used.
Based on above, I think Roku's weird clipping situation is best explained by his disc player outputing in a full range mode and his 45 detecting limited. But this will crush blacks as well as give faces sunburn and he doesn't report weird blacks.
Regarding the 45 Contrast control: My results above were all obtained at Contrast: Max, Brightness:50. The 45 contrast control cannot be used to recover highlights or shadows. At Max it doesn't clip blacks or whites in any agreed range. For WOW disc the white -1% star is clearly visible, while 0% is invisible. As it should be. When btb and wtw are clipped by any combination of the modes above, lowering the 45 Contrast from Max cannot be used to reveal clipped wtw/btb data. It works independently of brightness with no interaction with brighness. The Contrast control does not lower the black floor, but it does scale the shadows in linear proportion to peak white. It doesn't cause black clipping. It's a picture volume control.
Re 45 brightness control: 50 is the black floor. Anything above 50 raises the floor compromising blacks. Anything lower clips black data without lowering the floor. At 45 gamma 2.4 in a completely dark room the WOW black star field at 1% is just barely discernible at 50, and easily lost in any ambient light. It doesn't matter what lamp, signal mode or DR is selected, the 1% star sticks at the edge of black, barely discernible at 50. Increasing brightness to 55 makes the 1% star easily visible at cost of black floor and lower contrast. Increasing Brightness any amount past 50 hurts contrast in direct proportion to the brightness level. Lowering it any below 50 clips. The 3% black star is easily visible at brightness 50 with some room light. Raising gamma from 2.4 brings up 1% detail without hurting black floor, but to my eyes harms saturation and punch much more than shadows benefit gained. If you have an HTPC and watch stuff on the web you might want to normalize to it by choosing 2.2.
When PS3 and 45 are forced to RGB Full, the YCC disc data are scaled to use the full display and signal range of the 45.
To sumarize.
- Contrast Max loses nothing. Lowering it dims the picture.
- Raising Brightness can help bring out shadow detail in ambient light but in the dark sacrifices black.
- The 45 default brightness / contrast alignment is perfect for a home theater. All the data are there, perfectly aligned.
- 45 Dynrange is really just for RGB, but it does interact with player Ycbcr Superwhite. Why you'd want this for properly mastered YCC content is a mystery.
- 45 Clearwhite also has a mysterious purpose and makes peak whites look bad. Doesn't look useful.
HTH