Measurement And Calibration Methodology: How We Test
To measure and calibrate monitors, we use an i1Pro spectrophotometer, a Spectracal C6 colorimeter, and version 22.214.171.1244 of SpectraCal’s CalMAN software.
The i1Pro is very accurate and consistent measuring color on all types of displays, regardless of the backlight technology used. When we just need a luminance value, the C6 works better, especially in low light.
For patterns, we employ AccuPel DVG-5000 and DVDO AVLab TPG video signal generators. This approach removes video cards and drivers from the signal chain, allowing the display to receive true reference patterns. Connections are made via HDMI.
The AccuPel DVG-5000 is capable of generating all types of video signals at any resolution and refresh rate up to 1920x1080 at 60 Hz. It can also display motion patterns to evaluate a monitor's video processing capabilities, with 3D patterns available in every format. This allows us to measure color and grayscale performance, crosstalk, and ghosting in 3D content via the 3D glasses.
The DVDO generator is a new addition to our lab. It supports resolutions up to 4096x2160. We’re using it to verify the proper signal handling of QHD and UHD displays.
The i1Pro or C6 is placed at the center of the screen (unless we’re measuring uniformity) and sealed against it to block out any ambient light. The AccuPel pattern generator (bottom-left) is controlled via USB by CalMAN, which is running on the Dell XPS laptop on the right.
Our version of CalMAN Ultimate allows me to design all of the screens and workflows to best suit the purpose at hand. To that end, I’ve created a display review workflow from scratch. This way, we can be sure and collect all the necessary data with a concise and efficient set of measurements.
The charts show us the RGB levels, gamma response, and Delta E error for every brightness point from zero to 100 percent. In the table, we get raw data for each measurement. And the area in the upper-left tells us luminance, average gamma, Delta E, and contrast ratio. The individual charts can be copied to the Windows clipboard to easily create graphics for our reviews.
Every primary and secondary color is measured at 20-, 40-, 60-, 80-, and 100-percent saturation. The color saturation level is simply the distance from the white point on the CIE chart. You can see the targets moving out from white in a straight line. The further a point is from center, the greater the saturation until you hit 100 percent at the edge of the gamut triangle. This shows us the display’s response at a cross-section of color points. Many monitors score well when only the 100-percent saturations are measured. Hitting the targets at the lower saturations is more difficult, and factors into our average Delta E value (which explains why our Delta E values are sometimes higher than those reported by other publications).
mixed with the convenience for manufacturers of making mostly
1080 screens. When I hunted for a 2560x1600 screen last year,
I was shocked at the prices, because the same thing has happened
at 2560, ie. the market has narrowed in on 1440 height instead of 1600,
so the latter are now expensive (assuming one can find them at all),
eg. the Iiyama XB3070WQS-B1 is about 700 UKP, and the HP Z30i
is more than 1000 UKP.
At the least one positive from all this is that good 1200-height IPS
panels are now much more affordable. My first 1920x1200 IPS was
an HP LP2475W which cost about 450 UKP, but today the Dell U2412M
costs less than half that much (is the Dell better? Well, yes & no,
different feature set, etc., but the screen is nice).
I gave up on finding an affordable IPS 2560x1600, and meanwhile it
was obvious review sites had settled on 1440 height anyway (a few
years ago many sites were still testing wtih 1600 screens, but not
now), so I bought a Dell U2713HM instead which works pretty well,
except for its irritating resolution limitation over HDMI (watchout for
that if you buy a new screen, some models only support their max
res via DVI or DP - the Dell I bought can't do more than 1080 via HDMI).