An extension block that won't force chroma subsampling

[ralphonzolio]

First post here. I'm glad to see a forum dedicated to this.

I've had a 4:4:4-capable display for years (an LG 32LD450) and it's an ideal TV for a PC. Low latency, full chroma, and pretty much all the awful processing common on TVs can be disabled. For years I've had to run DVI to HDMI from an AMD card in order not to have forced chroma subsampling (resulting in horrible reds and magentas). Only by using DVI to HDMI and disabling the extension block can I get proper chroma. I just put together a new rig with an nVidia card, and, no surprise, it also forces chroma subsampling unless the extension block is disabled.

Why is any of this bad when I have a solution that results in ideal picture quality with 4:4:4 RGB? Because I have an HDMI 1.4a receiver and a full 7.1 setup I cannot utilize with my PC. I spent countless hours in 2011 trying to somehow get 4:4:4 chroma AND fully featured HDMI audio (7.1 PCM as well as DTS-HD/Dolby TrueHD) running 1.4a HDMI cables from PC HDMI to AVR HDMI, and AVR HDMI to display HDMI. I did a little EDID hacking with some old Japanese program, but no luck, and I don't think this place was around back then.

TL;DR: In theory, with a totally customized EDID with extension block, can I somehow get 4:4:4 Chroma (and 0-255 RGB obviously) AND HDMI audio? These things cannot be mutually exclusive. In fact, I know they're not according to the HDMI spec. Everyone knows most EDIDs are in some way wrong and it would seem mine, like most "TVs", report only 4:2:2 support in the extension block. Every time I look at my display I prove it supports beautiful 4:4:4.

I've been waging this war for years. Help me out!

(Please note the brokeness here has nothing to do with the recent nVidia workaround that achieves 4K resolution over HDMI 1.4a by forcing chroma subsampling. This problem has been present on both nVidia cards and AMD cards at least since the TV was released, and it applies to all AVRs. It is, or at least was, a very popular TV with the PC crowd and the issue I'm posting about is confirmed on AVSForum by countless other owners. Many other "TVs" that also support 4:4:4 suffer from the same problem.)

Edit: I was unclear about something. I've tested both HDMI straight to TV and HDMI to TV through AVR equally thoroughly. If a proper revised extension will produce a working override for one, then I have little doubt it will work for the other as well (though needless to say the AVR block will be more robust due to all the supported audio formats).

[ToastyX]

If you import the hdmi-bitstream.dat file in CRU, it should only be using RGB 4:4:4. If you need YCbCr 4:4:4, import hdmi-bitstream-ycbcr.dat instead, and set the color format in the video driver's control panel.

[ralphonzolio]

(12-28-2014 04:37 AM)ToastyX Wrote:  If you import the hdmi-bitstream.dat file in CRU, it should only be using RGB 4:4:4. If you need YCbCr 4:4:4, import hdmi-bitstream-ycbcr.dat instead, and set the color format in the video driver's control panel.

I've tried this on my usual DVI -> display connection and got subsampled chroma. That bodes ill for HDMI -> HDMI (or, with my AVR in the path, HDMI -> HDMI -> HDMI) but I will give that a try soon, probably tomorrow. Thanks for the quick reply.

[ralphonzolio]

Ok, I finally did some testing. HDMI to HDMI fared no different from DVI to HDMI even with the hdmi-bitstream.dat active. Extension block of any sort being enabled = forced subsampled chroma no matter what full stop, and this has been my experience with both AMD and Nvidia, Win 7 and 8.1.

However, with your tool I was able to achieve something nearly as good as pure HDMI (arguably better as I can keep my PC-specific display settings). I now have DVI -> HDMI from GPU -> display with 4:4:4 chroma, and HDMI -> HDMI from GPU -> AVR with audio. The DVI connection is set to primary, HDMI secondary, cloned display, with the straight-from-PC input of my display active (I ignore the AVR -> display input when using the PC and only use it for my consoles and DVR.)

Initially I got subsampled chroma with this setup until, of course, I used CRU to disable the display's extension block. The AVR EDID remains unchanged with extension block enabled. 7.1 PCM and all bitstream formats working Thanks for writing the utility. Assuming I don't run into any games that loathe display cloning as much as they loathe extended display modes, it looks like I'm set.