Measurement And Calibration Methodology: How We Test
A Quick Word About G-Sync Testing
G-Sync only affects synchronization between the video signal’s input and output refresh rate. Because of this, it either works or it doesn’t. There is no test we can think of that would demonstrate the superiority of its implementation in one monitor over another. For this, and all subsequent G-Sync product reviews, we’ll be sticking to our usual battery of display tests.
In the case of the PG278Q, we’ve added tests to determine the impact of ULMB (backlight strobe) on light output. You’ll find them on page ten.
To measure and calibrate monitors, we use an i1Pro spectrophotometer, a Spectracal C6 colorimeter, and version 188.8.131.524 of SpectraCal’s CalMAN software.
The i1Pro is both 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 and 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 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. The table shows us the 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).