Reason for White Clipping? - AVS Forum
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post #1 of 4 Old 05-11-2014, 04:01 PM - Thread Starter
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Hi Guys,

A year ago I calibrated my new TV with the PS3 as a source. Once I figure out the HTDV should be set to Limited range (as does the PS3), everything went smooth.
I decided to connect my Desktop PC to the same HDTV, as I want to be able to play Games and watch movies directly from my PC.

Here's the setup:

- ATI Readon 4850HD Card
- On Catalyst I set "4:4:4:4 Limited RGB" instead of "4:4:4:4 Full RGB" when the Desktop is connected to the HDTV
- The video card only have DVI, so I'm using DVI to HDMI adapter
- I'm using AVSHD Calibration tool

Calibrating Brightness was easy enough. The issues started on the 3rd pattern (White Clipping). Using "Windows Media Player" and "Windows Media Player Classic" I'm only able to barely see 230 to 232. Change the Contrast on TV does nothing to the Flashing bars, but instead changes how "Strong" the white color is.
I tried VLC, and I got different results - with VLC I was able to see 230 to 234, but again - changing the Contrast on TV did nothing to the Bars.

I noticed another strange thing that happens. On the First Pattern (Black Clipping) I set the brightness so I can only see 17 and above. But when I'm checking the Brightness with the second pattern (APL Clipping), no bars are being shown at all. I have to play again with the brightness to make them visible, and that ofcourse breaking the First pattern (I can now see bars all the way to 4-5).

Clearly, I'm missing something Important here that clipping the whites.
I'm guessing the Video Players have different settings, and maybe that explains the delta between the results (which makes it all more complex because I can't really be sure that Calibrate the screen on VLC, will have decent results while playing a GAME for example).

Thank you.
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post #2 of 4 Old 05-12-2014, 03:13 PM - Thread Starter
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Figured it out. It was all due to a problematic Video Card driver.
I downgraded from Catalyst 13 to Catalyst 12.4 and everything sorted out. Hopefully Radeon 4800HD owner will find this post usefull in the future, as 13 is the latest and that's what ATI suggests to install.

Thanks.
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post #3 of 4 Old 05-12-2014, 05:06 PM
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On my ATI card the Limited RGB option in the pixel format area appears to process everything as full range, which is generally expected for a computer, and then it converts to a limited range when the video is output. I can clearly see that switching to the Limited RGB option changes black and white levels, but when I pull levels on the computer they're always the same, regardless if the pixel format is set to Limited or Full. Assuming my drivers are not exhibiting any unintended errors, the video dynamic range has to be left at the Full (0-255) setting to avoid further compressing the range that would occur if the dynamic range Limited (16-235) setting was used while the pixel format was set to Limited. If this is the way the ATI drivers are expected to work, video ends up being converted from limited to full and then back to limited, which will likely result in the same sort of video grayscale rounding that happens with typical video playback on computers, such as the default video dynamic range Full (0-255) option. Unless the TV does not accept a full-range input, personally I cannot come up with a general benefit for using the pixel format Limited setting.
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post #4 of 4 Old 05-13-2014, 01:30 AM - Thread Starter
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Thank you alluringreality. I indeed went with 4:4:4 Full RGB for the same reason. Everything looks washed out on Limited.
I'm guessing that I'll be using the PC to play Video Games (which I'm guessing are mostly designed at Full RGB), and stick with my PS3 for Movies.
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