TV 'PC mode' questions

[iSeries]

Hi,

In the last couple of days I've been playing around with 'PC mode' on my LG plasma, which enables 4:4:4 support (trying to avoid having the TV convert to YCbCr and then back to RGB again). However, beyond that, I don't know what the TV is doing with the RGB signal fed from MadVR.

1. Is it likely that the TV is not doing any processing at all, and just displaying the RGB 4:4:4 signal as-is? Or could it be still converting to YCbCr, but in 4:4:4 instead of 4:2:2? Some of the TVs options aren't available in PC mode, however, the controls that I've read that would be greyed out if everything is 100% RGB are still available (saturation, tint, 20 point controls etc, the only controls locked out are controls I don't even use).

2. In 'PC mode', using the AVSHD black clipping pattern, bars 17, 18 and 19 look different that when in normal mode. EG bar 17 looks like there are three coloured bars overlayed on top of each other, one blue, one green and one red, and also slightly different lengths. Blue is the shortest, then green slightly longer, and then red slightly longer still. What would be the reason for this? And is this an issue? When in normal mode these bars just look like solid shades.

And a third question, not really related to PC mode, also applies to normal mode:

3. My TV seems to behave differently with 0-255 RGB than with 16-235. With the output chain of MadVR Full>GPU Full>TV full, the picture is ever so slightly darker and there is a small amount of black crush (bar 17 on clipping pattern flashes but using a different pattern it shows more clipping closer to black. I've read here that using full all the way is always the better choice, so do I live with the slight amount of clipping, or go with limited>full>limited, which does not show this clipping? Could it be my TV just works better being fed limited? What is it exactly that makes full>full>full the better choice anyway?

Any advice here would be greatly appreciated.

[huhn]

1. no one knows for sure.

2. sounds like a serious problem in PC mode.
there is no reason to do something odd like this.

3. while full range is best in theory it doesn't mean it will work best with every TV. some do strange things and it looks like yours is one of them.

i would give madVR limited GPU full and TV limited a try.

[iSeries]

Thank you huhn, I appreciate it

[iSeries]

It's been well stated around here that if fed YCbCr, and YCbCr is set in the driver, a GPU will convert it to RGB and then convert it back to YCbCr for output. Does this really still happen? Has anyone tested this to see if this still happens with recent GPUs / drivers? Is there really no such thing as a video equivalent to 'wasapi exclusive'? I really don't understand why it would be doing anything with it at all if 'use application settings' is set everywhere in the GPU driver, and the driver received output that matches the output setting in the driver. Why wouldn't it just pass it through? Is there an easy way to test it?

Knowing that my TV will convert RGB into YCbCr 4:2:2 for processing, is it at all possible that my GPU would do a better job of converting MadVR's RGB output to YCbCr than my TV can? (not that I necessarily think it's doing a bad job, just striving for the best my setup will allow). Again, is there an easy way to test this?

[huhn]

i can tell you that the nvidia sub sampling isn't good because i test it. and it is easy to do.

feeding YCbCr is already the first problem madVR can't do it.

a TV could do a high bit deep like 16 bit RGB->YCbCr conversation your GPU can't do that because it can't be send with the usually resolutions.

HDMI 1.4 can send 4:2:0 so there is absolutely no way to send an image unaltered.

[iSeries]

i can tell you that the nvidia sub sampling isn't good because i test it. and it is easy to do.

feeding YCbCr is already the first problem madVR can't do it.

a TV could do a high bit deep like 16 bit RGB->YCbCr conversation your GPU can't do that because it can't be send with the usually resolutions.

HDMI 1.4 can send 4:2:0 so there is absolutely no way to send an image unaltered.

Thanks again. So I've done a couple of tests and something weird is happening. I made two 3dluts, one with the TV in normal mode, and the other with the TV in 4:4:4 PC mode.

The 3dlut with the TV in normal mode, the AVSHD black clipping pattern bars are flashing normally as solid shades. If I then switch to the other 3dlut and put the TV in PC mode, the bars flash with that weird red, green, blue effect overlayed on top of each other. BUT - if I disable calibration from within MadVR, the bars flash normally as solid shades! I also switched to the other 3dlut to make sure it wasn't that, but the same thing, the weird RGB overlayed flashing bars. So it seems the TV's PC mode works just fine. With calibration disabled within MadVR, the bars are identical whether the TV is in normal or PC mode.

Is there anything special I'm supposed to do within Displaycal when the TV is in PC mode? I just used all the defaults for a MadVR 3dlut.

As for the slight black clipping when the TV is in full range mode, again, the issue seems to be with MadVR. If I disable dithering, near black shades are the exact same luminance whether a limited>full>limited chain or a full>full>full chain. As soon as I enable dithering again, limited>full>limited is slightly brighter than full>full>full.

I can't for the life of me work out what's happening here so any help is appreciated. My TV seems to be handling whatever it is given just fine.

[Asmodian]

It sounds like your TV is interacting badly with the 3DLUT. I had an older LG plasma (2010) that had a similar issue, as soon as you use add any color information at all the TV would start dithering bright colors to try to display that slight dark color, this means that when the 3DLUT adds a small amount of color (correcting the white point, etc.) it shows up in black and white test patterns like that.

I would suggest making sure you are targeting the native white point. Tune it to D65/6500K using the TVs controls but then in DisplayCal target native white, native brightness, and do not correct black.

I will also say that in the end I decided that my plasma TV offered better image quality when given limited range input. Your's may be different but I ran mine using limited -> full -> limited and was able to get a calibration I was mostly happy with. :o

4:4:4 is less important on plasmas, in my opinion, because they dither so much anyway. Color accuracy of fine details is not their strong point.

[iSeries]

It sounds like your TV is interacting badly with the 3DLUT. I had an older LG plasma (2010) that had a similar issue, as soon as you use add any color information at all the TV would start dithering bright colors to try to display that slight dark color, this means that when the 3DLUT adds a small amount of color (correcting the white point, etc.) it shows up in black and white test patterns like that.

I would suggest making sure you are targeting the native white point. Tune it to D65/6500K using the TVs controls but then in DisplayCal target native white, native brightness, and do not correct black.

I will also say that in the end I decided that my plasma TV offered better image quality when given limited range input. Your's may be different but I ran mine using limited -> full -> limited and was able to get a calibration I was mostly happy with. :o

4:4:4 is less important on plasmas, in my opinion, because they dither so much anyway. Color accuracy of fine details is not their strong point.

Thanks Asmodian, I did use the TV gain control to get the white point to 6500k (actually the report showed 6544k). I believe all the defaults in Displaycal target 'native' anyway, and I'd left all that alone. I'm not so concerned with 4:4:4, more with not having the TV convert RGB>YCbCr>RGB and just have a 100% RGB chain by having the TV in PC mode.

The weird thing is - with the 3dlut created with the TV in normal mode, all is good. Everything flashes on the black clipping test normally as solid shades. And yep it does appear my plasma behaves better with a limited>full>limited chain. So maybe it's just the way the TV interprets what it gets with a 3dlut when in PC mode that is the problem. Still don't know what the deal is with the difference between limited and full and MadVR dithering, and why there is a difference in brightness. Does limited require more dithering, and that in itself is making darker areas appear brighter?

One last weird thing - if the TV is in normal mode and I display the pink/purple 4:2:2 4:4:4 test in say MS paint, fullscreen, 4:2:2 is brightly displayed and 4:4:4 is basically invisible (as expected). However, if I play that in fullscreen with MPC-HC with the 3dlut enabled, both 4:2:2 and 4:4:4 are clearly visible. But then if I disable calibration within MadVR, It looks exactly like it does in Paint, only 4:2:2 is visible! Any ideas? And is it an issue?

[huhn]

The weird thing is - with the 3dlut created with the TV in normal mode, all is good. Everything flashes on the black clipping test normally as solid shades. And yep it does appear my plasma behaves better with a limited>full>limited chain. So maybe it's just the way the TV interprets what it gets with a 3dlut when in PC mode that is the problem. Still don't know what the deal is with the difference between limited and full and MadVR dithering, and why there is a difference in brightness. Does limited require more dithering, and that in itself is making darker areas appear brighter?

no it doesn't require more dithering. the problem is most likely just your TV.

One last weird thing - if the TV is in normal mode and I display the pink/purple 4:2:2 4:4:4 test in say MS paint, fullscreen, 4:2:2 is brightly displayed and 4:4:4 is basically invisible (as expected). However, if I play that in fullscreen with MPC-HC with the 3dlut enabled, both 4:2:2 and 4:4:4 are clearly visible. But then if I disable calibration within MadVR, It looks exactly like it does in Paint, only 4:2:2 is visible! Any ideas? And is it an issue?

sharpening does the same so i'm not wondering what this is happening.

[iSeries]

sharpening does the same so i'm not wondering what this is happening.

The sharpening must be happening within MadVR then - because sharpening is disabled on the TV. And of course the pattern displays as expected with MS Paint. But then, I don't have any sharpening active in MadVR, and if I disable the 3dlut then the image displays normally with MadVR rendering it. So, I'm at a loss.

[huhn]

the point is this iamge only works if you are sending it before changing it but you are changing it so i'm not shocked by it.

[Asmodian]

The sharpening must be happening within MadVR then - because sharpening is disabled on the TV. And of course the pattern displays as expected with MS Paint. But then, I don't have any sharpening active in MadVR, and if I disable the 3dlut then the image displays normally with MadVR rendering it. So, I'm at a loss.

It is also possible for the 3DLUT to change the colors such that when blended they don't match the background.

I had a lot of trouble calibrating mine, it has a sort of auto dimming where a small square at ~15% area of 100% white would be much brighter than one even 30% of the screen area. This made any gamma curves taken with different patch sizes very different. I ended up using a very small patch size and letting the TV compress it as it saw fit, everything done with a larger patch came out with a weird gamma.

[iSeries]

It is also possible for the 3DLUT to change the colors such that when blended they don't match the background.

I had a lot of trouble calibrating mine, it has a sort of auto dimming where a small square at ~15% area of 100% white would be much brighter than one even 30% of the screen area. This made any gamma curves taken with different patch sizes very different. I ended up using a very small patch size and letting the TV compress it as it saw fit, everything done with a larger patch came out with a weird gamma.

'A lot of trouble...' man don't even get me started lol. Plasmas are clearly a nightmare to 'calibrate', if you can call it that, as like you say, different window sizes etc completely change the outcome. It took a looooong while to go through all the combinations of window sizes and backgrounds. Finally hit upon 4% window size and 36% linear light background. My wife has the patience of a saint lol.

[iSeries]

Well, it appears my AVR is the issue. Connecting directly to my TV, PC mode works just fine, no issues at all. Odd though, the AVR doesn't have any video processing capabilities, it's supposed to just pass through whatever it gets. Obviously not the case!

[dwaleke]

What AVR do you have?