Color misalignment fix for HTPC users! - AVS Forum
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post #1 of 3 Old 09-02-2009, 11:27 AM - Thread Starter
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Hey all,

I have a Panasonic AX200U and after about 6 months it developed a visible color alignment problem. On black/white borders I could clearly see a red line and it was starting to drive me crazy. So a few months ago I implemented a fix for this into XBMC, my favorite HTPC software (which is open source). The solution is simple - XBMC deliberately shifts the colors in the opposite direction of the alignment problem so that when the projector projects the image it will be aligned correctly.

I'd just been using it in my own personal builds since then but recently the XBMC devs made some changes that made it a bit simpler for other users to try this change. If you have a projector with color alignment problems and you use XBMC as your HTPC software then check out the steps below to get the fix!

1) Download http://wolfeden.ca/files/XBMC/yuv2rgb_basic.glsl, save it to XBMC/system/shaders/ (overwrite the one that's there)
2) Open up the yuv2rgb_basic.glsl in your favorite text editor (NOT NOTEPAD)
3) Start XBMC
4) Tweak your shift values, save the file, and play a reference video in XBMC to check the result. Instructions about how to edit the shift amounts are at the top of the shader file... basically, look for "EDIT HERE" and change the three lines below that. They're in the format vec2(x, y) where x and y are the percentage of your screen you want to shift the color (positive values are right and up respectively).
5) Every time you start a video the shader is reloaded so you can tweak your shift with XBMC open and just restart the video again to see the changes.

Notes:

1) You will need an XBMC revision higher than 22449 to use this feature (this means not the official 9.04 release). Windows users can go here for a recent version, Mac/Linux users should probably build from source (check the XBMC forums for help).
2) This will not work while using VDPAU under linux
3) This can only get you within 1px and will never be perfect - there's no 1:1 correlation between your misalignment and the RGB pixels on the screen.

If this is a popular feature then I'll pressure the devs into accepting changes that will make this feature a bit simpler to use, so please let me know if you are using it. If you have any questions feel free to post up and let me know.

Nic

P.S. I wasn't sure if this was technically supposed to be in the HTPC forum but I thought it made much more sense in the (cheap) projectors forum - if that's not the case feel free to move it mods.
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post #2 of 3 Old 09-02-2009, 11:32 AM
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This is a huge thing. Thanks for the post, will try it out with my HC5500 as it is a bit out, but not too bad. Makes you wonder why the projector makers don;t just build this in the firmware?
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post #3 of 3 Old 09-06-2009, 04:34 PM - Thread Starter
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Well looks like there's not much interest - this "feature" will probably stay as it is then.
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