OSSC Pro: HDMI Full RGB Black Clipping

[spacetime66]

There is some slight black clipping with OSSC Pro when the source, AV4 input and video output are all set to Full RGB when viewing the Lagom LCD Black level test on PC … one above black is the same as the black background no matter how high I raise the brightness on my display… when I connect my PC directly to the display with Full RGB output set in the nvidia control there is no black clipping as one above black is distinguishable from the black background especially when I raise the brightness… is this something that could be fixed via a setting or by firmware update? Also the black clipping happens in both A-LM and scaler modes.

• This topic was modified 1 year, 3 months ago by spacetime66.
• This topic was modified 1 year, 3 months ago by spacetime66.

[BuckoA51]

Just to check, that test is available on the page here? http://www.lagom.nl/lcd-test/black.php

[spacetime66]

yeah that is the page of the test I mentioned

[Zacabeb]

Does this also affect peak white (255 being clipped to 254?) The thing that comes to mind is that with limited range video, values 0 and 255 at 8 bpc are reserved for embedded sync and metadata, a limitation inherited from SDI. Maybe the HDMI sink in the OSSC Pro accidentally clips those values even with full range input where said limitation shouldn’t apply?

[spacetime66]

I just tried an Tendak hdmi to vga apater with input AV3 with full range rgb set in nvidia control panel and VGA out via the extra av out board and one above black in the Lagom LCD Black level test is now clearly visible when the brightness is raised on PC CRT moniitor… if I use hdmi full range in and extra av vga out one above black is clipped and If I use Tendak hdmi to vga with AV3 input and hdmi out full range one above black is also clipped… maybe the slight black crush is due to the HDMI DACs?

• This reply was modified 1 year, 2 months ago by spacetime66.

[marqs]

I looked into this shortly, and it seems HDMI RX chip has AV code insertion enabled by default which overwrites 0x00 and 0xff values in the video stream. Disabling the feature seems to have fixed the issue.

[spacetime66]

Are you sure the HDMI TX chip isn’t doing something similar? because when I used my Tendak hdmi to vga transcoder via vga in on the ossc pro and ossc pro’s hdmi out 1 above black was clipped but when I used my Tendak hdmi to vga transcoder via vga in on the ossc pro and vga out via extra av out board on the ossc pro the clipping was gone…

[marqs]

0x00, 0x01 and 0xff values can be all seen from both VGA & HDMI inputs when HDMI output is captured.

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