3D LUT Calibration - Page 2

If I understand this right. (still new to LUT etc)

The box would be placed between your screen(input) and output media (blu-ray player as example) to do LUT conversions.
The box would have to accept various formats and resolutions etc acceptable for the chosen interface, and outputs the same but takes the data through the 3D lut table for correction.
It takes the input data and then does LUT transformation with the LUT placed inside it(which should be updateble with new and correct tables for the different device hooked up) and just output the data anew in same format as it got but with corrected colours, etc through that 3DLUT.

I understand such that the box is only really needed for non-PC hooked up displays. As if your pc is the source you can do the LUT conversion at the PC in the first place. But the device would have uses though with PC's as well as if you move the display to another computer you just move the Box with it and get same image. Though taking into consideration your PC's both used the same output format. For example fullRGB 4:4:4, and not changed it for YCbPr or etc in the same switch. (otherwise the LUT would need to be remade)
Or would it be more advanced that the box has capabilities to recognize the input format and do format conversations on the spot as well.
For example. it recieves a YPbCr 4:4:4 format but you can with the box pick it to transform it to YPbCr 4:0:0 as output unto your display with the aditional LUT corrections.
Other like fRGB to YPbCr be possible? This would require some switches or buttons to change between the conversions.

The prices mentioned here seem quite high to me. Damn high to be honest.
How will this be for home users if the little box and software will cost as much or more than their displays?

I could see a huge potential for the box if it's cheap.
You hire or buy a calibration and with this get the box with the service. Or your bought it separately. All you need now is a LUT table made, which your hired calibrator could come over to you to take measurements from your display to create the table with which he loads unto your little box. At same time maybe a little display setting is needed for the LUT to work optimally. But the process would be more automated than before by not needing going through every option in your display tweaking them all little by little while taking new measurements to see that results are good as the normal now manual calibrating of setting your TV correctly for example...
All the small tweaks and setting would be instead automated through measurements and following calculations to adjust the LUT matrix for correct gamut,gamma,saturation, colors etc which 3DLUT was capable of adjusting in appropriate software.

You just place the measuring device and connect and start the procedure in the software as it measures and calculates the appropriate table values for your LUT.
Lastly you just load the generated LUT into the box and check it's correct?

The format conversion ability of the box would be a major use-ability bonus. If it would recognize the input format and has choosable conversions you would not need to do a new LUT for each and every source if the output from it to the box is diffrent as long as you keep it to the display.
The box would allways output the desired correct format to the display but switch which conversion depending of the box. This way you it would be most useful for a end home user as he can use the box with any device as long as it's paired with the display it was matched for. Not needed a new LUT for every different source. But it would probably increase cost and development.

It's a bit cheaper than the alternative. Which would be the VideoEQ Pro from AVFoundry/Spectracal.

Depends on what you use..

yCMS - Color Management System


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I understood what you were posting about - past PC implementation(s) limitations.... yCMS has only been available for a few months and not many know about it.. however, it's an exciting offering for HTPC users and the developer is active...

It's also not system wide.

There is a built-in LUT for windows (system wide), but it just allows you to balance gamma and grayscale.

You can use 3dluts with full gamut correction on a PC , its a question of doing the transform in software rather than with the graphics hardware. ICC profiles are a case in point.

Of course.

I wasn't refuting that you can do a 3dlut on the PC, just that they aren't system wide. They require the application to be specifically aware of the profile.

Yes true but people have been using 3dluts with software hooks on PCs for about 15 years by my reckoning. I don't deny that 3dlut calibration is the way to go ( can't understand why Calman haven't implemented it) and I also can't understand why every single playback app out there doesn't just support it as a a matter of course.

What I would like to see is a universal playback app, BD/dvd/files/DVR type functionality with a profile based 3dlut CMS. This is precisely what John Adcock was trying to do to Media Center with his Upsilon Mixer and to be honest he got this particular feature pretty much there and managed to support a wider range of sensors than I've seen in just about any other system.

I'm still of the opinion that the humble PC is the absolute best video playback device in terms of quality vs cost. A properly setup PC can outperform even the extremely high end standalone systems and has the potential for so much more in terms of optimising the path of consumer video to display.

(profile based calibration , automatic colorspace switching by format, advanced scaling algorithms , advanced chroma upampling , linear filtering stages, advanced deinterlacing and cadence detection , meaningful post processing , AV sync adjustment , frame rate adjustment, non-orthogonal image transforms to name a few).

However it gets constantly hamstrung with badly implemented apps from devs who don't seem to know anything about maintaining and optimising video ( arcsoft and cyberlink for example). The only way we are ever going to get this fully unified is if someone writes a fully functional playback system from scratch that supports every possible video playback scenario someone could want.

The best implementation of 3DLUT on PC I would see to be on the graphics card driver or similar last place where the image output is last at.
Just have the out signal sent out through whatever dvi/hdmi/DP.. go through the 3DLUT in a final stage.. and voilÃ* you have system wide correction and no hassles meaning the it's not prone to bugs etc issues and actually works in it's implementation. (this is maybe a good idea to ask for the Linux side ATI Open driver team to implement? if it's not already?)

The problem with CMS and LUT's on PC's is that the tables and corrections get overrided by various programs creating a mess... or the "profile" is for compatible software only that implements that systems implementation...

It should really only be placed and implemented at one point at all for system wide correction. You can then have specific application if they need other tables do a additional conversion within their application borders like photoshop... But you still have that one last 3DLUT for the whole system doing it's magic.


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For software that takes 3DLUT? I think MPC-HC could do something like that. Never really figured out how to use it though or found any relevant information on where the LUT would be loaded and how to create the appropriate 3DLUT for it. Just were a lack of information with the little searching I did.

Agree that would be the ideal solution, for me the most promising avenue is either MCE or XBMC once they get the DVR stuff sorted out. I've never had much luck with MediaPortal and MPC-HC can play back a lot but isn't integrated.

MadVR has some great features too, pity it doesn't yet work with live TV or with DXVA.

But a decent all round solution still seems some way off although I've been surprised by the progress towards blu-ray playback in xbmc and the other open source players.

Applying a 17x17x17 3d lut is almost embarrassingly trivial, it's getting the lut that's hard.

John

MPC-HC recently added code to leverage lcms to turn a ICC profile into a LUT which is then applied to the video, results where not great on my system.

John

If you are writing the playback app then applying a 3d lut is just a small bit of shader code and as long as you're careful with the offsets in the interpolation it's straightforward.

Here's the MPC code

http://mpc-hc.svn.sourceforge.net/vi...99&view=markup

the tex3D is the 3d lookup.

If you don't build the player then things are more tricky, that's where my product comes in

John

I think the ideal solution would be windows implementing it in the WDDM 1.2 drivers or whatever windows 8 uses so anyone could drop a 3dLUT in.

That would also solve a huge problem with panel matching, and wouldn't require any additional hardware per display.

At least on the PC.

Obviously if you are just doing a home theater system then a video processor is a good option, but it does beg the question how much better is a 3d LUT vs the 1D LUT + CMS that's been around for ages?

FWIW, my video renderer "madVR" supports applying 8bit input 16bit output 3dluts. All mentioned bitdepths are per component. The resulting 3dlut files are 96MB. I admit that this might seem like overkill, but it runs fluidly with all current GPUs and allows ultra accurate gamut and gamma correction. madVR does all its processing via GPU hardware in 32bit+ floating point per component (temp buffers are 16bit integer per component). The final result is dithered down to the output bitdepth. I think this should achieve the best possible quality.

As JohnAd correctly said, applying a 3dlut is not a problem at all. Very easy to do with a GPU, just use a volume texture with trilinear interpolation. Creating a 3dlut is the real issue.

AFAIK there are currently 2 solutions which can create 3dlut files for HTPC playback:
- yCMS
- Upsilon Mixer

Both can create 3dlut files accepted by madVR. But sotti is right, madVR only applies these for video playback. So the computer desktop, photo applications etc do not benefit from the 3dlut.

I'm not aware of any external hardware that can apply 3dluts in a satisfying manner. IMHO 3dlut output should be high bitdepth (not even sure if 10bit is enough). And the result needs to be dithered down to the display output bitdepth. Which external hardware can do that? If you compromise on bitdepth and/or skip the dithering step, you'll end up with banding problems.

Even though I still agree that it would be a good solution due to its broader effect, unless they also go with 16 bit per component bit depth for the desktop resolutions it would be a lesser solution than madVR for watching movies. The YCbCr->RGB conversion results in float values, so, rounding the resulting values to 8 bit RGB (the current max bit depth) before feeding them to the 3DLUT would be worse than keeping the precision until the end and then feeding the 3DLUT using trilinear interpolation, like madVR does.

That's surely true for gamut/colors. But I think for black & white movies a perfect grayscale is crucial and there a bit more than 17 measurements might be beneficial to achieve a perfect grayscale. Of course it also depends on the display. If the display is nearly linear in its response then less measurements will do. But if the display response has a lot of funny unexpected bumps then more measurements might be needed to achieve a perfect grayscale.


For non-HTPC users that's definitely true. But many HTPC users (including myself) only use their HTPC and have no further sources. For such people application specific LUTs can be all that is needed, depending on the setup.

I know, was just trying to keep it simple. B&W movies do use a very limited subset of colors, of course, and for best quality playback their "grayscale" (as in darkest to brightest shades of colors used by a given B&W movie) needs to be as smooth as possible. And I think having a 17x17x17 cube that spans the entire gamut might be too coarse to achieve perfect results if the display has a very bumpy response.

Ok, maybe I'm a bit paranoid here. Maybe with most displays a 17x17x17 cube is all that is needed to achieve near perfect results. But as a developer and a perfectionist I'm usually not satisfied with "most" and with "near perfect". So I would personally rather go overkill, just to be on the safe side.

This is an exciting concept for this home user and calibration enthusiast. Given reasonable pricing I am a candidate for a box for each of my displays. Thank you, Steve, for your efforts.

The attachment is extracted from the Light Illusion site. The parameters are a 10 point cube and a 5 second frame rate. Total time to create the LUT is 1 hour and 23 minutes.


Creating the same LUT with an i1Pro requires a 10 second frame rate so the LUT creation would take 2 hours and 47 minutes. Plus, the i1Pro requires black readings every 10 minutes.


Would a 10 point cube be the standard for accuracy for our home displays?

What about creating a 17 point cube for maximum accuracy? How much more accuracy would be gained? I guess my real question is, could/would we see it?

Thanks for the information. A 17 point calibration by anything less than the Hubble would take a long time - ie. i1Pro = 13.65 hours if my calculation is correct.

I saw in another thread where you said another meter (can't remember which it was) didn't need 10 minute dark readings) yet it is "common knowledge" on this forum that the readings are required. I guess I'll start a separate thread to sort it out.

Edit: Better yet, I just wrote X-Rite Support and should have the answer within 24 hours.