AVS HD 709 - Blu-ray & MP4 Calibration - Page 137 - AVS Forum
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post #4081 of 4094 Old 10-26-2014, 09:24 AM - Thread Starter
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By default most computers use a full RGB range, which uses 0 for black and 255 for white. Video instead uses 16 for black and 235 for white. In order for video to fit with the full RGB range typically computers will expand video so that 16 goes to 0, 235 goes to 255, the video information between 16-235 is expanded accordingly, and any possible video information from 1-15 or 236-254 is removed. In this scenario of playing video on a computer that outputs a full RGB range, you would only expect to see the 17-234 bars flash on the clipping patterns.

Video expansion on a computer is a practical way to get video to fit with the full RGB range commonly used for computers, and using video expansion is easily the most common way to play video on a computer. From a video purist standpoint expansion is not necessarily ideal, since the ideal is to pass the original video information to the display without such alteration. One item introduced from expansion is grayscale banding. Because there are 256 values for black through white in the full RGB range and only 220 values for black through white in the video range, some grayscale values are assigned a step of two digits, instead of the original intent that all grayscale steps would be a single digit. Fortunately most video includes color information, and the amount of strictly grayscale information in most video is limited, so usually the grayscale banding from expansion will not be noticeable. Another argument against expansion is how it removes the video information outside the 16-235 range. Certainly there is information that decodes outside the 16-235 range from a lot of video, but usually the majority of the information outside 16-235 appears to be due to video compression in my opinion. There are people that consider these sorts of topics to be their profession that claim video often contains "specular highlights" above 235, but personally I was never able to happen to run across any examples to support such claims, which makes sense considering most people are unlikely to ever be able to notice how expansion limits the range to 16-235 when watching video on a computer. Basically expansion is an easy way to play video on a computer, and it's uncommon for the effects to be noticed, but from a video purist standpoint the general recommendation would be to pass video information from the video player to the display with very little alteration.

Often video driver or video playback software will have controls to affect expansion. There can be ways to set a Windows computer to decode at least some video so that black remains at 16 and white remains at 235, and the entire video grayscale from 1-254 is retained within the computer output. The issue with this scenario is that the video values may no longer match the computer desktop, so you might have a black level at the desktop that does not match the black level from video, and you would need some way to switch between the two outputs. If your video card has two outputs you might be able to setup one display input for video as 16-235 and one display input as 0-255 for computer desktop use, but most people don't care to go to this sort of trouble in dealing with two non-matching levels from their computer depending on what task they are doing. So video drivers and video software may have controls to affect how expansion is handled in some situations, but for convenience usually video is expanded to match the full RGB range when using a computer.

Last edited by alluringreality; 10-26-2014 at 09:29 AM.
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post #4082 of 4094 Old 11-04-2014, 05:28 PM
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alluring reality, should I set my amd driver settings to pc standard full rgb or limited studio? I know limited is better for video, but I assumed jriver with built in lavfilters automatically changed that when playing video? or am I kidding myself and I should use rgb limited on my HTPC all the time? I only play video on my htpc

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post #4083 of 4094 Old 11-05-2014, 01:04 PM - Thread Starter
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If you only use a computer for video, you could try setting it to output video levels. I think on my AMD card the limited range setting under the video properties with the default RGB full pixel format setting was one way that seemed to avoid any obvious video expansion, and my TV can be set to accept that sort of input. Generally I don't use my computer primarily as a video player, so I haven't used those settings enough to say for sure if there might be any items to specifically watch out for in various situations.

I'm not familiar with the video playback software listed, but the video patterns here may be able to help you to determine how various software might affect the video, and you may find that the patterns display differently depending on which settings you select. For example by looking at the color clipping pattern I found that the Blu-ray player software I bought a few years ago decoded color differently than the other video players on my computer, as indicated by the bars that flash depending on the player used. Some video players will allow you to check RGB values with programs like colorcop or a print-screen, but other video players will have copy protection that doesn't allow such ways to easily check RGB values. Basically I can't really provide specific settings for what you want to do, and even if I could, it still would be a good idea to try to check for yourself how your computer is operating, since I've personally seen some video driver versions with errors that caused video to playback differently than what would be expected from other versions.

Last edited by alluringreality; 11-05-2014 at 01:11 PM.
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post #4084 of 4094 Old 11-05-2014, 04:29 PM
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thanks alluringreality, I'll play around with it. what difference should I notice? better black levels in video?

Gear list: Main setup - Kef Q900, Svs sb12-nsd subwoofer, onkyo 609 receiver, epson 8350 projector, elitescreens sable 92" screen, mac mini htpc
bedroom setup: PSB Image B5, maverick tubemagic a1 amplifier, hifimediy sabre9023 dac, ZMF Fostex T50RP modded headphones
preordered gear: Light Harmonic Geek Pulse X dac and headphone amp
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post #4085 of 4094 Old 11-05-2014, 07:07 PM - Thread Starter
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Assuming things are set correctly, you have a display that is able to equally accept video or computer levels, and the display level matches light output for black and white, I'll suggest there probably is little reason to necessarily expect readily-noticeable differences depending if you are using video or computer levels. For example, I doubt if I could quickly pick out if I was looking at a limited or full-range signal in a blind test on my TVs. It's possible that items such as the previously mentioned grayscale banding or loss of video information above reference white might be noticeable from video expanded to computer levels in certain situations. Generally for those sorts of reasons the recommended practice is to deliver video levels to the display, but considering how common video expansion is used for practical reasons on computers, generally I wouldn't expect most people to be able to easily pick out differences with a majority of commercial video content.

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post #4086 of 4094 Old 11-08-2014, 09:11 AM
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I'm trying to calibrate my display which is connected to a HTPC, but I've got the issue where nothing below 16 ever flashes in the Black Clipping test pattern, and nothing above 235 ever flashes in the white clipping test pattern. Regardless of whether I have the brightness/contrast set to 0 or 100 the same lines flash, so it's impossible to calibrate.

Reading through some of this thread I thought the issue would be that my PC was outputting the full colour range (0-255) instead of the video colour range (16-235). In the Intel Graphics Control Panel there's a section under Video->Input Range, which by default is set to Application Settings. I changed it to Driver Settings and Limited Range, but this didn't solve the problem. I also read that outputting YCbCr might solve the problem, so I enabled that but it didn't help.

I'm at a bit of a loss. Should I be able to make lines below 16 and above 235 flash or am I misunderstanding the manual? If they should, can anybody suggest what might be going wrong in my setup?

I'm using the MP4 test patterns with:
Graphics Chip: Intel HD4000
OS: Windows 7
Codec Pack: CCCP
Media Player: MPC-HT with MadVR for output
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post #4087 of 4094 Old 11-08-2014, 09:32 AM
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I've been messing around with this for six hours and then a minute after writing that post I found the problem. After typing "with MadVR for output" at the end of the post I started to wonder if that was the issue. I had a look at the MadVR options and found a setting to output 16-235, and now everything is working.

Sorry for the above post. Unfortunately I can't edit/delete it, so please just ignore it.

Thanks a lot for the test patterns
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post #4088 of 4094 Old 11-09-2014, 08:39 PM
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Hey there, I'm having an issue with VLC. I tried using the first file, Black Clipping, and the only bars that flash are 18+, no matter how high I set the brightness. Is this a VLC issue or does my TV just suck that much?
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post #4089 of 4094 Old 11-09-2014, 08:41 PM
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oops, sorry, apparently I should read up more. Would edit my post if I could.
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post #4090 of 4094 Old 11-09-2014, 09:12 PM
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Okay, I fixed it in MPC-HC + madVR, but I can't find a way for VLC to output 16-235, even after a lot of googling... does anyone know how to?
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post #4091 of 4094 Old 11-15-2014, 03:31 PM
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Hi,

I tried the whole evening to calibrate my display, without success.
Whatever limited/full settings on both tv and video driver I choose, only 19+ bars flash.
With full range, the display is washed out.
With limited it's seems OK (the dark are really dark) but changing brightness doesn't work. The bars bellow 19 are not visible, instead of 17.
Any suggestions?
For the record, I use xbmc on windows, with Intel 4600 driver set as limited and Sony hx920 as limited too.
Thanks
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post #4092 of 4094 Old 11-21-2014, 08:48 AM
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How is this going to help in 2014-2015 when the last update was in 2010?
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post #4093 of 4094 Old 11-21-2014, 08:58 AM
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Quote:
Originally Posted by bbace View Post
How is this going to help in 2014-2015 when the last update was in 2010?
Welcome to AVSForum.

What is it not doing that you want it to do?

The standards it addresses have not changed since 2010. If it was correct then it is correct now.

4K and Rec 2020 are coming in now. I suspect they will require a new project.

-Bill
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post #4094 of 4094 Old 11-23-2014, 01:35 PM
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So I played this on my Samsung 4K 55 inch set through various sources

The results for black bars were consistent (brightness). However the results for white bars (contrast) were all over the place.

1 - via USB plugged into TV port - Almost all white bars upto 253 were blinking.
2 - via youtube app on samsung - Almost all white bars upto 253 were blinking
3 - via apple TV connected via HDMI to Samsung - Only 3 white bars below blinking (rest were all white). Changing contrast setting had no impact.
4 - via roku 3 connected via HDMI to Samsung - Only 3 white bars were blinking (rest were all white). Changing contrast setting had no impact.
5 - via Tivo premiere via HDMI to Samsung - Only 4 white bars were blinking (rest were all white). Changing contrast setting had no impact.

Colors were spot on. But I am confused about the inconsistencies shown above. What could be going on? It seems to be the HDMI connectivity. I know there is some basic knowledge that is escaping me.

Please help.
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