VG248QE Color Accuracy with G-Sync - Pro Calibration

[MonarchX]

You have to remember that a 6 bit color palette only has 64 steps. When you attempt to modify your gamma curve, you are running into a granularity problem at the lower end of the scale. For example (making up numbers) normally working with 8 bit color your 20% target may be 5,7,3 and 30% may be 12,17,9. With 6 bit color your 20% target may be 2,3,2 and 30% may be 6,7,5. Trying to hit D65 exactly at the low end is going to be literally impossible. Then you add in the dithering. Dithering doesn't magically give you more dynamic range. What it attempts to do it so add more granularity through averaging. You may get a 2,2,1 / 3,4,4 checkerboard pattern instead of 2,3,2 and so on. Then when you take this logically a step further, you realize that a solid checkerboard field is the best case scenario. When you look at ramps for instance, the monitor does it's best to dither adjacent pixels of slightly differing luminances together as best it can. This is most likely the culprit for the tinting you are seeing. When you are attempting to micromanage the lower end with a LUT, you are for instance making 20% white slightly blue, 25% slightly red, 30% slightly green, etc. When the monitor is then mixing all these together with dithering, you are probably getting a tint from the interaction.

There are only 64 steps per color at most, and that the act of trying to change the white point lowers this even further for at least 2 of the primaries. At best you will get an approximation of what you want. This is where your professional skills will come into play. You will have to determine what the most acceptable compromise is. The meter does it's best to approximate human vision, but in the end you have to determine what looks most natural to the human eye.

Take what I say with a huge grain of salt as I'm not a professional calibrator. I highly recommend heading over to the avs forum display calibration area. It's one of the greatest resources online for calibrators:

http://www.avsforum.com/f/139/display-calibration

As for your questions about using ULMB, you would probably be best to direct them at either the forum I linked to or the company that you purchased your probe and software from. The strobing back light may cause the probe's results to be inaccurate. If so, this may be addressed by calibration software that takes this behavior into account.

I joined AVS Forums a while back and while they were generally helpful, they weren't as helpful as you have regarding this very issue.
I understand what you are saying, but the levels that have whichever tint continue having that exact tint without any change at all. I can see interaction, but that is not what is causing the effect... There are areas that are practically impossible to calibrate, regardless of the white balance setting used. I had it even worse with my original VG248QE, so I had it replaced with this one, which was somewhat better, but still sucked like I explained. I am not seeing the checkerboard pattern anywhere, btw... something I saw other people talk about, but I just do not see it...

In this test - http://www.lagom.nl/lcd-test/gradient.php the dark 0-10% or so is like a giant purple band, then 10-20% or so looks very neutral, and then 20-100% are fine with only LUT interpolation banding, which I could care less for. Its the 0-10% that destroys my gaming experience as no amount of WB manipulation, which is quite impossible to do anyway, makes the purple turn neutral. I think its not just not capable of doing it... And that is with 350:1 contrast ratio...

The non-LightBoost mode is better, but still has that un-calibrate-able purple band 0-10%, even after calibration.

This is just very interesting to me from a professional point of view - I never ran across a display device other than my own monitor, that would behave like this. Not being capable of producing gray is just... out of whack!

I did see others complain of the same tint, but now it seems nobody except for me gets that purple band 0-10% of the grayscale ramp. I was hoping G-Sync would fix it, but now it doesn't look like it will. At least now I know to save the money instead of expecting G-Sync to normalize 0-10% somehow.

[TSM]

No, I'm definitely seeing the blue in the 0-10% area of the gradient pattern you linked to here as well using the same display but with the g-sync upgrade. It appears to be inherent to the display, and like you said it's probably uncorrectable by the end user. You might want to contact ASUS about as it could be firmware correctable. It may also be that with the 6 bit color range that 1 step of blue below that level makes the luminance too dim and 1 step of red/green above that makes the liminance too high. It may be that way because ASUS engineers decided there's no better compromise to be made.

I'm sorry I misunderstood earlier, but when you linked the gradient pattern it became obvious what you were talking about. I intentionally didn't go looking for problems with this display as I knew I would find many. Moving my head around while looking closely at that gradient pattern you linked to was also cringe inducing. I mainly bought into g-sync because I decided that fluidity of movement was more important to me in gaming then 100% correct visuals at all times.

As an aside, moving to the g-sync upgrade gets rid of the tinting that happens on non g-sync monitors in lightboost. The reason non g-sync monitors have that tint is that lightboost mode was explicitly for using a 3D vision or similar kit. The tint is meant to color correct for the 3D glasses. With the g-sync monitors, they are making lightboost available to all applications and have eliminated the tint for all times that you aren't explicitly using 3D vision. I bought this monitor with the kit already installed, so I'm not sure how much improvement the kit brings otherwise. It is however extremely convenient to just hit a single button to turn lightboost on/off.

[spacediver]

OK, that makes sense. But that should only apply to native hardware characteristics, like contrast ratio, luminance, colorspace, native gamma, white balance, etc. Calibration should fix all of that, but it doesn't. 6500K is 6500K and when its achieved using balanced R, G, and B - the reddish.purplish tint should go away, but it doesn't.

6500K typically refers to correlated color temperature, which, for 6500K, can range anywhere from d65 to a purplish or greenish tinge. I think you meant to say d65.

[MonarchX]

A few more things:
- If 3D glasses really ARE green-tinted and require a specific standard where B and R are elevated, then what kind of a calibration should be performed? I saw some 7500K profiles out there - is that the standard to use if I am to watch 3D movies/games?
- Does it also mean that the regular LightBoost mode will have green tint even if it is properly calibrated to D65? It does not seem to be the case after my calibration
- What about ULBM - why doesn't it have elevated B and R to make up for 3D glasses green tint? Is 3D available on ULBM?

I am debating whether I want to sell it and get the Eizo, but it will cost way more. I already have an awesome TV for very high image quality, so a good TV for SP games + fast G-Sync monitor for fast MP games seems to make more sense for the money. Anyway, I'll make up my mind eventually.

[TSM]

Assuming that the only color correction done by 3D mode is altering the white color temperature, then you should be able to correct it just by doing a normal grayscale calibration. If the monitor or drivers are actually altering the color decoder, then it's going to be more involved. I'd just start with the grayscale as you have already done. If 3D mode plays with the gamma, you'd have to correct for that as well. You can then check the color decoder using test patterns and see how far you are off on your primaries and secondaries after doing the grayscale. As long as you are in the ballpark, you should be alright. If you have some serious abnormalities, then you are going to have to start tinkering. There is no reason you can't eventually end up with a good calibration. It's just a matter of how much work it will take.

Nvidia realized that people wanted back light strobing at 120 hz as a standard feature and created a mode that doesn't do the color correction. Thus ULMB was created. 3D uses the strobing back light by default and doesn't have any other fancy name like ULMB. When you specifically engage the 3D vision mode, it turns on the color correction. Otherwise the color correction is disabled. With a g-sync monitor the drivers only engage the color correction specifically when using 3D mode.

Theoretically the only correction done by 3D mode is altering the color temperature and your post calibration image should be identical to one done in ULMB. You won't know until you get in there and start measuring.

Personally, if you don't want g-sync upgrade, then I don't see why you'd choose the ASUS over it other then cost. The ASUS is arguably a better gaming monitor, but the Eizo is far and away a better monitor overall. If you are in it for g-sync, then it's the only game in town at the moment.

[MonarchX]

OK, so you're saying that a normal D65 profile is all that I need for the real 3D Mode because NVidia will just enable correction for green tint? I thought I would have to make a specific LUT for the 3D Mode that takes green tint into consideration. I admit I am not all that knowledgeable when it comes to rarely-used standards. I know 9300K is a cold/blue temperature, 6500K is a warm/reddish temperature, but what kind do I need to offset NVidia 3D green tint? I am not sure I want to trust NVidia's color correction - its not likely accurate.

BTW, I managed to get a really great calibration LUT for the 144Hz mode. I re-profiled my colorimeter and used ArgyllCMS Ultra quality calibration, which took more than an hour, making insane number of readings and using very tight dE tolerances. The end-result is quite awesome - the purple band is still there, but it got smaller, way smaller! I SO suggest using ArgyllCMS for the most accurate LUTs. I have CalMAN v5 Enthusiast (includes CalMAN RGB) and its nowhere as accurate as ArgyllCMS at making LUTs.

I have another question though - I know that 60Hz and 144Hz have different gammas on regular VG248QE, and 60Hz is supposedly better-looking. So, when you use G-Sync, does that mean that color accuracy/quality goes up and down based on your FPS? That would be a big problem!

[TSM]

As someone pointed out before using 6500K or 9300k is meaningless. 6500K is actually a small range of colors. D65 is the standard which is specifically x=0.31271, y=0.32902. You can get an exact 6504K color temperature and still have it not be D65. Much like all thumbs are fingers, but not all fingers are thumbs.

Here's how I would set the color temperature in that situation. Make sure that windows color management is completely disabled. This is important because you need to be reading the end results for your monitor. I would then lower the contrast on the monitor to something really low so that there is a lot of headroom (probably 50% or less of the contrast with such an extreme color shift). Display a 255, 255, 255 white test pattern (this would be a 109% grayscale pattern if you were calibrating a display using video standards). Then I would use the red/green/blue drives on the monitor and your colorimeter or spectrophotometer to achieve D65 (.313, .329). Then you are going to want to run continuous measurements with your meter and watch the x and y coordinates. As you raise the contrast on the monitor watch the .313, .329 coordinates and at some point while raising the contrast they are going to change. Go a couple clicks past that point and you will notice the same number changes by a little every time you raise the contrast by 1. If .313 drops, you have run out of red contrast (you would be at step 255 out of 255 for red on an 8 bit monitor). If .329 drops, you have run out of green contrast. If both of the numbers start going up, you have run out of blue contrast (this won't happen). Once you see the numbers change, back off 1 on the contrast before the point it started changing, and this will be your maximum contrast setting. Keep in mind that you might have to tweak the drives as you raise the contrast if it the color temperature shifts slightly as you raise the contrast. Now you should be at D65 at the top end. The bottom end you are going to have to correct using color management (ICC profile).

Obviously if the frame rate of the display affects things like gamma and color temperature something like g-sync is going to cause your results to vary as the frame rate varies. While in g-sync on the ASUS the display is running in a quasi 144 mode. All screen updates are at 144hz, but it doesn't update the display unless a new frame is available or you have fallen below 30hz.

You also have to remember that the actual temperature of the monitor will affect it's performance (hot room vs cold room or warmed up vs recently turned on for example). A lot of calibration is realizing the limitations of the display and making the best compromises. Quirks, flaws, bugs and actual display limitations will creep up preventing you from achieving your "perfect" calibration. Even if you manage a perfect calibration, the lighting in your environment throws a lot of it out the window as well.

[spacediver]

Then I would use the red/green/blue drives on the monitor and your colorimeter or spectrophotometer to achieve D65 (.313, .329). Then you are going to want to run continuous measurements with your meter and watch the x and y coordinates. As you raise the contrast on the monitor watch the .313, .329 coordinates and at some point while raising the contrast they are going to change. Go a couple clicks past that point and you will notice the same number changes by a little every time you raise the contrast by 1. If .313 drops, you have run out of red contrast (you would be at step 255 out of 255 for red on an 8 bit monitor). If .329 drops, you have run out of green contrast. If both of the numbers start going up, you have run out of blue contrast (this won't happen).

HCFR's real time measurements show chromaticity, and they also show Red Green and Blue balance. If you customize your white point to D65 in the advanced/references (which it should be at by default), a balanced RGB indicates the D65 target has been achieved. It's a useful way to visualize the relationship between changes in the CIE xy domain, and the RGB domain, and is extremely useful for making adjustments in the RGB domain.

[TSM]

Yeah, I use HCFR. I've always wanted to try some of the other software, but as I'm only doing it for my own displays I never could convince myself to spend the money when HCFR gets the job done.

[MonarchX]

As someone pointed out before using 6500K or 9300k is meaningless. 6500K is actually a small range of colors. D65 is the standard which is specifically x=0.31271, y=0.32902. You can get an exact 6504K color temperature and still have it not be D65. Much like all thumbs are fingers, but not all fingers are thumbs.

Here's how I would set the color temperature in that situation. Make sure that windows color management is completely disabled. This is important because you need to be reading the end results for your monitor. I would then lower the contrast on the monitor to something really low so that there is a lot of headroom (probably 50% or less of the contrast with such an extreme color shift). Display a 255, 255, 255 white test pattern (this would be a 109% grayscale pattern if you were calibrating a display using video standards). Then I would use the red/green/blue drives on the monitor and your colorimeter or spectrophotometer to achieve D65 (.313, .329). Then you are going to want to run continuous measurements with your meter and watch the x and y coordinates. As you raise the contrast on the monitor watch the .313, .329 coordinates and at some point while raising the contrast they are going to change. Go a couple clicks past that point and you will notice the same number changes by a little every time you raise the contrast by 1. If .313 drops, you have run out of red contrast (you would be at step 255 out of 255 for red on an 8 bit monitor). If .329 drops, you have run out of green contrast. If both of the numbers start going up, you have run out of blue contrast (this won't happen). Once you see the numbers change, back off 1 on the contrast before the point it started changing, and this will be your maximum contrast setting. Keep in mind that you might have to tweak the drives as you raise the contrast if it the color temperature shifts slightly as you raise the contrast. Now you should be at D65 at the top end. The bottom end you are going to have to correct using color management (ICC profile).

Obviously if the frame rate of the display affects things like gamma and color temperature something like g-sync is going to cause your results to vary as the frame rate varies. While in g-sync on the ASUS the display is running in a quasi 144 mode. All screen updates are at 144hz, but it doesn't update the display unless a new frame is available or you have fallen below 30hz.

You also have to remember that the actual temperature of the monitor will affect it's performance (hot room vs cold room or warmed up vs recently turned on for example). A lot of calibration is realizing the limitations of the display and making the best compromises. Quirks, flaws, bugs and actual display limitations will creep up preventing you from achieving your "perfect" calibration. Even if you manage a perfect calibration, the lighting in your environment throws a lot of it out the window as well.

Thank you TSM - I am very familiar with what dynamic range is and I always calibrate at least 20 minutes after turning on the screen, but most of the time give it good 30 minutes. I also give my i1D3 a dry run or two.

I do not think I am getting my point across at all... I have no big issues with D65 calibration, except for that purple band. I was talking about the LightBoost mode. You stated that LightBoost mode, the original, has blue and red tint to compensate for the green tinted 3D glasses... There has to be an exact calibrated amount of that extra blue and red to accurately compensate for the green tinted 3D glasses. I was asking about a specific temperature or some kind of a standard that has more of blue and of red than of green, so I can calibrate to that standard.