Calibration Overview
One of the greatest improvements you can make to the quality of your video image is to get your display device calibrated. In order to keep things consistent, the vast majority of video production companies worldwide have agreed upon a series of standards for color settings. Video calibration involves measuring the current output of a display device, comparing that output to the defined standard of your choice, then modifying the display settings of your output device to come as close as possible to the standard.
It sounds simple, but it can get tricky - especially if you don't have the right tools for the job. Professional calibrators certainly have the tools, but I wanted to give it a shot myself. After researching all the available options, the tool I chose to calibrate my Marantz VP12-S2 DLP projector was the ColorFacts CF-6000 package from Milori Software. Milori is a small company who has been making a lot of noise recently (and upsetting their competition) with their powerful solution. I initially learned about ColorFacts through the AVS Forum, where I met and became friends with Milori Software's CEO, Mark Hunter. Mark has been extremely valuable in helping me get the best possible image from my projector by using ColorFacts.
Before I continue, I should explain a little bit about how video calibration works. There are many ways to measure the output of a video device, but most experts agree that the four primary metrics are:
- Color Temperature
- Luminance
- Black Level
- Contrast Ratio
There are volumes of information available on each of these measurements, but I've created some simplified definitions below.
1. Color Temperature
When calibrating a device, the goal is to achieve a consistent color temperate across a wide spectrum of images output from a video source (such as a DVD player). Currently, the most popular color temperature standard for theater use is 6500 degrees Kelvin (commonly referred to as 65K). The amount of output from the video source is measured in IRE units (which comes from the Institute of Radio Engineers) and is expressed as a percentage of pure white. For example, 0 IRE is pure black, 50 IRE is a medium shade of grey, and 100 IRE is pure white. Therefore, the goal when calibrating color temperature is to achieve a consistent 65K color temperature at every IRE level between 0 and 100. Most commonly, this is done by tweaking the individual red, green, and blue (RGB) output settings of the displaye-1_ice.
2. Luminance
The simple definition of luminance is brightness, or the amount of light (measured in units called lumens) that is emitted by an area of the display screen. The luminance of a properly calibrated display device should curve upward smoothly from 0 IRE to 100 IRE. That curve is often referred to as a Gamma Curve.
3. Black Level
A device's black level is the level of brightness on the screen when the source is displaying 0 IRE. Black level varies from video display to video display with better displays having a better black level. If a display device has a bad black level, colors are less "saturated" and will appear somewhat washed out, while black images will tend to appear dark grey. Some reference standards define 7.5 IRE as Video Black, and 0 IRE as Pure Black or Blacker than Black.
4. Contrast Ratio
A device's contrast ratio is comparison of two numbers, derived by a mathematical calculation that compares the amount of light output (measured in lumens) at 100 IRE compared to its light output at 0 IRE. Without discussing the equation at length, suffice it to say that a higher contrast ratio (such as 3000:1) is better than a lower one (such as 10:1). Video calibration should aim to achieve the highest possible contrast ratio from a display device.
Enough with the terminology, let's get to the results! All the following readings were taken with a GretagMacbeth Eye-One spectroradiometer connected to a laptop running ColorFacts 2.5. The sensor was mounted on a tripod facing the screen a few feet away. The Marantz VP12-S2 DLP projector shoots approximately 20 feet on to a 123" Stewart GrayHawk Microperf screen. I calibrated three different sources, but the results I'm including in this article are from a Marantz Marantz DV-18mkII DVD using the Avia video test DVD. Special thanks go to Darin Perrigo (whom I met on AVS Forum) for his help in my initial calibration attempts.
Setting Device Primaries
Device Primaries are numbers that refer to the color gamut (range of all colors) that a display device is able to create. Setting them accurately in a calibration program allows the software to maximize the accuracy of the analysis instrument. ColorFacts has a wizard for measuring the device primaries, but I used the following values, which I obtained from an unnamed but extremely reliable source:
|
x |
y |
Y |
| Red |
0.6440 |
0.3460 |
0.1560 |
| Green |
0.3730 |
0.5960 |
0.7372 |
| Blue |
0.1470 |
0.0790 |
0.1068 |
| D65 White |
0.3127 |
0.3290 |
1.0000 |
|
|
|
|
Using those numbers as the device primaries, my ColorFacts CIE Chart for the Marantz VP12-S2 looks like this:
Pre-Calibrated (Default) Measurements
To establish a baseline (and to satisfy my curiousity), took readings in ColorFacts from 0-100 IRE and graphed RGB, Luminance, and Color Temperature histograms of the projector's default factory settings. Here's what the default RGB settings looked like:
Default RGB Historgram
Notice on the RGB histogram that the red and blue values in the images are high compared to the green value. This would logically translate to an image that was too purple, which is exactly what I was seeing with the naked eye.
Here is what the Color Temperature histogram looked like with the default settings:
Default Color Temperature Historgram
This graph really shows the need for calibration. Below 30 IRE, the color temp is high, but becomes too low below about 35 IRE. A good color temp histogram should be as flat as possible at 65K throughout the entire spectrum.
Finally, I graphed the Luminance histogram:
Default Luminance Historgram
It looks pretty good, but still could use some minor tweaking to make sure I'm not "crushing" my blacks.
Tweaking the Settings
Using the ColorFacts software and the Avia test DVD, I was able to display full screens of 0 IRE through 100 IRE test patterns while I modified the projector's output settings and got real-time feedback through the software. When my adjustments were done, I achieved the best results with the following settings for each of my three sources and projector inputs:
| Component Input: DVD Player |
| Preset: | Theater 2 |
|
Contrast: | 75 |
| Brightness: | 45 |
|
Color: | 60 |
| Sharpness: | 1 |
|
Color Temp: | Middle |
| Contrast Red: | 106 |
|
Brightness Red: | 121 |
| Contrast Green: | 131 |
|
Brightness Green: | 132 |
| Contrast Blue: | 120 |
|
Brightness Blue: | 116 |
|
| Component Input: Xbox |
| Preset: | Dynamic 1 |
|
Contrast: | 70 |
| Brightness: | 44 |
|
Color: | 60 |
| Sharpness: | 9 |
|
Color Temp: | Middle |
| Contrast Red: | 106 |
|
Brightness Red: | 121 |
| Contrast Green: | 131 |
|
Brightness Green: | 132 |
| Contrast Blue: | 120 |
|
Brightness Blue: | 116 |
|
| RGB Input: PC |
| Preset: | Standard 1 |
|
Contrast: | 75 |
| Brightness: | 47 |
|
Color: | 58 |
| Sharpness: | 7 |
|
Color Temp: | Middle |
| Contrast Red: | 101 |
|
Brightness Red: | 131 |
| Contrast Green: | 126 |
|
Brightness Green: | 125 |
| Contrast Blue: | 121 |
|
Brightness Blue: | 125 |
|
Calibrated Measurements
Once I had made all the adjustments to my display device settings, my ColorFacts charts looked much better. Here's what the calibrated RGB histogram looks like:
Calibrated RGB Historgram
Notice that the three color channels are all relatively close to each other from about 40 IRE and up. They look good to the naked eye below 40 IRE, but there is not enough light output to measure reliably with the size of my screen and the throw distance. I plan on redoing this measurement with the updated software.
Here is what Color Temperature histogram looked like after my calibration:
Calibrated Color Temperature Historgram
This shows the vast improvement over the default color temp. It is close to flat at 65K throughout the entire spectrum.
Finally, here's the calibrated Luminance histogram:
Calibrated Luminance Historgram
It looks pretty good, but I can see some room for improvement. I'll be messing with this some more when I install the new software version.
Conclusions
People can spend thousands of hours (and dollars) trying to get their display images to look "reference." But the bottom line should always be that the image looks good for you. After my initial calibration attempts, I can already notice a much higher quality image, and in the end, that's all that matters. I will continue to tweak the settings and post any updates here!
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