Note: Even though I mention some Epson projectors specifically, this method can be applied just as effectively to all projectors. In fact, this calibration philosophy is applicable to all display devices.
Stereomandan’s Calibration Method for Epson 1080 (partial), 1080UB, 6100, 6500UB, 7500UB, 8500UB, 8700UB...
From my discussions with folks here, I’ve discovered that the CMS (Color Management System) behaves the almost the same on all the projectors listed above (except the 1080 which doesn't have brightness control in the CMS, so a Epson 1080 owner will only get partial benefit) This means that my method listed below will perform roughly the same with any of these projectors. (Personally, I own the 1080UB the early brother to the 6500UB, 7500UB, 8700UB...)
As a side note. I have not had a chance to fool around with the THX mode on the newer models. I believe this mode is closer to the correct REC.709 standard than other presets on older models, but still can benefit from this method.
While performing detailed calibration of my 1080UB, I discovered that I could achieve what most would seem almost a perfect result. My primary and secondary color and brightness lined up perfectly with the REC.709 reference points, my gamma tracked dead-on 2.22, and my grayscale was fantastic at 6500K with a dE of less than 2 from 20% to 100% stimulus. Here is an example of my calibration, which I was extremely happy to achieve. Doesn’t get much better than that huh? Well, read on.
I noticed that areas of scenes looked washed out(gray), and as if color had been reduced. The picture was better than the "out of the box" settings though. While the picture looked good, it lost a lot of that colorful POP wow factor. It was most noticeable in mildly lit scenes. When colors were subtle, they looked washed out. The problem was particularly noticeable with skin tones, which are critical. Faces looked too gray, and the picture just looked flat. Outdoor, well lit scenes didn’t seem to suffer as much.
What did I do?:
I tried to understand why colors looked washed out. This led me to the Color Saturation Windows in the downloadable AVSHD REC.709 disk found here:
I had been using this disk for my calibration, but had simply been using the 75% or 100% Brightness Color windows for calibration. This is what is commonly used, and the standard method for calibrating. See the top two arrows in the picture below:
For more background information, look here at Kurt’s Dummies Guide for calibration, a fantastic source of information.
Important Information before you read on:
Color terminology. I will be discussing Color Brightness Windows, and Color Saturation Windows. They are NOT the same. When most people talk about using 75% or 100% color windows for calibration, they are talking about the Color Brightness windows. The saturation does not change between these 75% or 100% color windows. (the x, y locations remain the same.)
Using my calibration method, you will use the 75% Saturation windows (which are at 100% Color Brightness). I’ll explain why later, and where you can find the patterns.
In order to understand what I mean, let’s take a look at the color gamut triangle. Shown below is the color gamut from above, but with some explanations. Take the green primary for example (at the standard REC.709 reference point.) Let’s say you were to pull up a 100% brightness color window for green. If you measure the Green location to be outside the REC.709 triangle, then it is oversaturated. If you were to measure the green primary and it was inside the REC.709 triangle, then it is undersaturated. Adjusting Hue spins the measured point around the D6500 reference white point, as shown. The goal is to get the measured value of green to match the reference point of the test pattern. This chart does not show the brightness of green, another critical measure. You can have green perfectly saturated and the correct hue, but it can still be to too light, or too dark. This is why there is a x, y location for all colors, but also a Y (Brightness) value. All three have to be set correctly to have an accurate color.
O.k., with that said; let’s say you want to find out how accurately your projector displays more subtle colors of green, closer to the center 6500K white point in the color gamut. Are there test patterns for this? Yes, but the only ones I’m aware of are on the AVSHD REC.709 disk. They are listed in the Color menu, under saturation windows, as shown below.(the bottom arrow) Here are where the 75% Saturation windows are located (as well as 0%, 25%, 50%, 75 and 100% color saturation windows for all primaries and secondaries.) All of these patterns use 100% brightness (Y) as their reference. The patterns also assume your display gamma is 2.22. (By the way, the 6500K white point, shown in the photo above, is where all of the grayscale measurements are located, from black all the way on up the grayscale to white. This gray, "middle area", of the triangle is where there should be no noticeable color.)
This is where all of these saturation windows are located on a color gamut chart:
Don’t confuse these with the standard 75% and 100% Color Window patterns shown below. These are the color windows found on most calibration disks. These color windows are only at the outer edge of the color gamut triangle, but the brightness (Y) is either 100%, or 75%. Here are where they are located on the AVSHD REC.709 disk.
So, what happens when you calibrate our Epson projectors to the standard color windows? Take a look below. The 100% saturation points, at the outer edge of the triangle look great, but look at the 75%, 50%, and 25% saturation points for all the colors. Pretty surprising huh? Let’s take green again for example. When green is supposed to be 75% saturated, it will really only be close to 50% saturated! The same holds true for other colors. This is why I noticed the colors looking gray and washed out! It was really happening, as the measurements show.
So what do we do? Well, after studying my calibration files, I noticed that the 0, 25, 50 and 75% saturations seemed to perform o.k. after some adjusting, but then all heck broke loose at 100% saturation and became oversaturated. So I thought, well, maybe I can at least get the 75% saturation gamut(and lesser saturations) to look great. This 75% gamut is outlined by the light gray triangle in the picture above. This makes up a LOT of the available colors to choose from. The 100% saturation points will be off, but maybe this is overall a better solution.
So here are the results:
The 0, 25, 50, and 75% saturation points line up fantastic, and the 100% points are oversaturated. How does the picture look in real life, on the screen? Fantastic! Skintones are spot on, and WOW, the colors look beautifully accurate and have good POP. I’ll explain more below.
How do you do this? Open up the saturation windows and use the 75% saturation window patterns for calibrating, instead of the typical 100% saturation windows. Here is a walkthrough:
Colorometer (I used the Display One LT when performing calibrations for this guide, and have since upgraded to an i1pro. All of the suggestions in this method still apply)
Download the ColorHCFR software:
Laptop or PC close to the screen
Tripod (to hold meter)
Blu-Ray Source settings:
Turn off any picture enhancement modes (sharpness, contrast, dynamic…)
If you are going to use 24fps for viewing, turn this on
Projector Initial Settings:
Color mode: Natural (yes, this matters. Do not use the Theater Black Modes)
Turn off any Frame Interpolation.
Iris: Off (Can be turned back on after calibration is complete)
Choose either low or high lamp mode, but don’t switch during calibration session. You will need a separate calibration for each mode if you are going to use both high and low lamp mode. (This only impacts the grayscale, so that’s all you need to adjust for each mode)
Color = -10 (this gives a good starting point)
Tint = -4 (this gives a good starting point)
Color temp = 6500K, or 6000K
Skintone = 0
You can turn on 2-2 or 4-4 pull down if the Blu-Ray player is set output 24fps
HDMI expanded (Depends on Blu-Ray player setting for Blacker Than Black and Whiter Than White setting)
1) Brightness = Set by eye with AVSHD pattern
2) Contrast = Set by eye with AVSHD pattern (I typically bump my contrast down two to four notches from what the test pattern would suggest. I had problems with overdriving the bulb when adjusting to meet the test pattern. This does sacrifice some lumens though)
3) Adjust grayscale using the gray window patterns on AVSHD (I use the 90% and 30 or 40% gray windows) You typically don't mess with Green, unless you have to. Only adjust Blue and Red to match Green. Use Gains first with the 90% window, and get the red, green and blue levels equal. Then use the Offsets to adjust the 30 or 40% window, again making red green and blue equal. You may have to go back and forth a few times between the 90 and 30 window to get the correct setting. Remember, gains first on the bright windows, then offsets for the darker windows.
4) Recheck brightness and contrast, and adjust as necessary. Sometimes, adjusting the Gains and Offsets can impact the correct brightness and contrast setting, particularly brightness.
5) Adjust gamma. Use the Custom Gamma. My spreadsheet below helps with setting custom gamma.
My Excel Download
For this, I recommend using my spreadsheet. Instructions on how to use the spreadsheet are in the first post of the thread in link to below. I've attached a copy of this file at the end of this post as well. This spreadsheet has been a HUGE help for me. I developed it because I was tired of constantly calculating the correct gamma brightness, and also the primary and secondary color locations, and brightness. To use the spreadsheet, you copy and paste data from HCFR into the excel spreadsheet. It provides charting, target locations for colors and brightness, dE calculations... For your initial calibation, you only need to use the "Calibration Aid" tab. Here is the link:
Go to the Calibration Aid tab. Enter the measured Y value of your 100% Gray window from HCFR. See the pictures below:
Then, using the custom gamma sliders in the EPSON, adjust your Gray windows brightness to match the target Y values (cells N14 thru N24). You will need to adjust the gamma sliders for the 10%, 20%...90% windows. I start with the 90% window, and adjust that, then go to the 80% window and so on until I finish with the 10% window. Some gamma sliders impact more than one brightness window(especially the sliders to the far right), some only impact one (sliders to the left). The sliders on the left affect the darker windows, while the sliders on the right adjust the bright windows. Don't touch the first or last slider! (they impact your 0% grey, and 100% grey, which is brightness and contrast which you've already set)
Alternatively, I’ve included a table that shows the %Y for each gray window, shown below. (this is more work than my spreadsheet, but the table is provided in case you don't have Excel) For instance, the 30% gray window should measure 6.91% of the 100% gray window. If your 100%Y reading is 20 cd/m2, then the 30% window should read 1.38 cd/m2. This needs to be repeated for the 10-90% windows. Do NOT adjust the 0% or 100% window. (the first and last gamma slider bar). I like my gamma to be 2.22 for all windows except the 10% window, which I like to have at 2.15 gamma to improve shadow detail and prevent black crush.
Gray Window\tRelative to 100% Y 0%\t 0 10%\t 0.60% 20%\t 2.81% 30%\t 6.91% 40%\t 13.08% 50%\t 21.46% 60%\t 32.17% 70%\t 45.30% 80%\t 60.93% 90%\t 79.14% 100%\t 100%
6) Adjust Color Gamut
I go in this order. Red, Green, Blue, Yellow, Cyan, Magenta.
Example of 75% saturation Window
Here are the x, y locations and %Y for each color at 75% saturation.
\tx\ty\tRelative to 100% Y Red\t0.5582\t0.3298\t0.213 Green\t0.3032\t0.5323\t0.715 Blue\t0.1907\t0.1273\t0.072 Yellow\t0.3927\t0.4612\t0.928 Cyan\t0.2466\t0.3288\t0.787 Magenta\t0.3189\t0.1979\t0.285 White\t0.3127\t0.3290\t1.000
If you use my Excel spreadsheet, in the Calibration Aid tab, it will make it easier because the target brightness is also shown. When you adjust saturation on the Epson, the brightness will change. As you increase saturation, the brightness will go up and vice versa. Be aware of this. Your goal is to hit the x, y locations for the 75%, and the correct Y. For example, let’s say your 100%Y reading is 25 cd/m2, then Red should hit 5.33 cd/m2 and Green should hit 17.88 cd/m2, and so on. You need to calculate the Y for each color. My spreadsheet does this for you automatically if you enter the 100% Y value.
I have found a very easy way to hit the correct color locations. This takes away the headache of trying to hit x, y locations (as shown above) and how you adjust saturation and hue to get there. See the red, green, and blue bars in the HCFR picture above? (three pictures back) In the picture, the bars show 98%, 100%, 100% to the left of the ftL and cd/m2 readings. These are the bars I'm talking about. Here are the target %'s for the red, green, and blue bar for each 75% color saturation location. (They are also listed in my Excel spreadsheet on the "Calibration Aid" tab as shown a couple of pictures back).
\t Red Bar Green Bar Blue Bar Red Primary\t 378%\t24%\t24% Green Primary\t 15%\t133%\t15% Blue Primary\t 64%\t64%\t555% Yellow Secondary 106% 106% 17% Cyan Secondary\t 24%\t120%\t120% Magenta Secondary 247%\t41%\t247%
For example, lets say you want to calibrate red. To hit the correct saturation, all you have to do is increase or decrease the red saturation slider in the Epson RGBCMY menu until the red bar reads 378%, and the Green and Blue bar read 24%. If the green and blue bars are not equal, use hue to correct this. Hue is always used to balance colors. When calibrating blue for example, you want green and red to be equal. This creates the correct hue. When adjusting a secondary color, like yellow for example, you want an equal balance of green and red. (red and green will have a high %, while blue will be low.)
Keep in mind that you still need to set brightness (Y) for red, and all the colors The target value will be shown in the "Calibration Aid" spreadheet, or you can calculate it based on the 100% gray window. Remember, calibrate red, green, and blue before you calibrate the secondary colors.
That’s it. You’re done! Enjoy. You will notice that your 100% colors are oversaturated, but your brightness at these locations will also drop. (I'll write up some more on this later) This helps compensate for the oversaturation. I have found this method to look far superior to the standard method of using the 75% or 100% Brightness Color Windows. If the Epson CMS worked 100% accurately, we would not have to use my method. You could use the standard method.
O.k., so I mentioned that I would explain the brightness drop at 100% saturation, and why this is a good thing. The error in a color (Delta E, or dE) uses saturation, hue and brightness in it’s calculation. This means that if a color is oversaturated, you can use a lower brightness to fool the eye into thinking the color is less saturated. This works, but there are limits.
As you can see from the results above, when you use my 75% saturation technique, the 100% locations are oversaturated. What does the brightness of each color do as you increase saturation from 0 to 100%? Look at the picture below. It stays well behaved up to 75%, but then drops at 100%. This drop in brightness helps compensate for the oversaturation. This is why the 75% method provides a picture superior to the standard calibration method even though the 100% points are oversaturated.
Edited by stereomandan - 12/4/13 at 10:20am