Display Testing Explained: How We Test Monitors and TVs

Grayscale Tracking, Gamma Response and Color Gamut

Grayscale Tracking

The majority of monitors, especially newer models, display excellent grayscale tracking (even at stock settings). It’s important that the color of white be consistently neutral at all light levels from darkest to brightest. Grayscale performance impacts color accuracy with regard to the secondary colors: cyan, magenta, and yellow. Since computer monitors typically have no color or tint adjustment, accurate grayscale is key. Grayscale tracking is the one thing that’s adjustable on nearly every computer monitor and HDTV. Even the least-expensive products typically have a set of RGB sliders. HDTVs usually have a high and low range, known as a two-point control, and a few have a 10-point adjustment.

Our standard is 6500 Kelvins, which matches all computer- and video-based content mastered with the Adobe RGB or sRGB color space.

The chart shows RGB levels at every brightness point from zero to 100 percent. A perfect result places all the bars level at the center position. If one bar is higher than the others, that’s the tint color you might see if the error is great enough. The Delta E graph shows the amount of error at each brightness point. It’s generally accepted that errors less than three are not visible to the naked eye.

Depending on the monitor’s color temp and picture modes, we may show several charts to give you an idea of a product’s uncalibrated performance. We always calibrate when possible, even if the gains are small, to show you a display’s full potential.

When we compare monitors, the lowest average Delta E value comes out on top.

  • Patterns used: Gray Step, Gray Fields 0-100 percent
  • Lower average Delta E values mean more accurate grayscale tracking

Gamma Response

Gamma is the measurement of luminance levels at every step in the brightness range from 0 to 100 percent. It's important because poor gamma can either crush detail at various points or wash it out, making the entire picture appear flat and dull. Correct gamma produces a more three-dimensional image, with a greater sense of depth and realism. Meanwhile, incorrect gamma can negatively affect image quality, even in monitors with high contrast ratios.

In our gamma charts, the yellow line represents 2.2, representing the most widely used standard for television, film, and computer graphics production. The closer the white measurement trace comes to 2.2, the better.

In professional monitor and HDTV reviews, we also test for compliance to the BT.1886 gamma standard. Introduced in 2011, it is slowly replacing the 2.2 power function in film and television content. The differences are subtle. But in practice, it shows just a bit more shadow detail and greater contrast in mid-tones and highlights.

To compare displays, we chart the gamma tracking (difference between highest and lowest values), and deviation from the standard in percent.

  • Patterns used: Gray Step, Gray Fields 0-100 percent
  • Computer application standard: 2.2 power function
  • Video content standard: BT.1886

Color Gamut And Performance

Color gamut is measured using a saturation sweep that samples the six main colors (red, green, blue, cyan, magenta, and yellow) at five saturation levels (20, 40, 60, 80, and 100 percent). This provides a more realistic view of color accuracy.

Like the grayscale tests, we show color charts that illustrate each product’s different picture modes, as well as a final one with calibration results. It’s easy to see in the example which colors are closer to or further from their targets. The goal is to have the dots within the squares.

The luminance chart shows a third dimension of color, which is how bright it should be. If a bar is above zero, that color is too bright. Below the line is too dark. An ideal chart would show no bars at all!

The final Delta E value is calculated from the CIE and luminance results. Obviously, lower is better. You can track the accuracy of all six colors at five different saturation levels on each of the three charts.

  • Patterns used:Color Bars; Red, Green, Blue, Cyan, Magenta, and Yellow Full-Fields
  • Lowest average Delta E error means more accurate color
  • Standards: sRGB, Rec.709, Adobe RGB, DCI & Rec.2020 where appropriate

Gamut Volume: Adobe RGB 1998 And sRGB

Gamut volume is a specification used by the photo industry to benchmark monitors. It’s just another way to measure color accuracy, so we include the metric in addition to the gamut tests above. Manufacturers usually quote a volume number in their specs like 100 percent of sRGB or 70 percent of Adobe RGB. Our test simply verifies that claim.

Using CalMAN and QuickMonitorProfile, we create an ICC profile from our measurements. Then we use Gamutvision to calculate the volume with respect to both the sRGB and AdobeRGB gamuts.

  • ICC profile generated with QuickMonitorProfile using x & y coordinates from our gamut measurements
  • Rendered percentage of sRGB and Adobe RGB 1998 gamuts
  • Standard: 100 percent
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