Chroma Test Setup for Complete Gamma Measurement on Video Signal Generators

Displays measure the gamma value to correct the compatibility between our perception of brightness and the actual intensity of the light source. The images below show the effect of gamma correction on the same photo; the larger the gamma value, the more distinct the details in dark regions, while the display effects in bright regions decrease. Too high gamma values will reduce the image quality, so display manufacturers generally set the gamma value between 1.8 ~ 2.4.

The two graphs below plot the human perception against the brightness and grayscale signals from the display, following the gamma function L = aVγ+Lb defined by VESA in the Flat Panel Display Measurement Standard (302-5A). The brightness perception figure on the left depicts the response of the human eye to changes in brightness; the gamma 2.2 curve on the right is the curvature of the black to white curve as output by the monitor. Quantitative research has found that the human perception of brightness is a non-linear curve; we are slower at detecting brightness changes at high brightness than at low brightness. Therefore, adjustment of the gamma value makes the displayed brightness come closer to the perceived brightness by the human eye.

CHROMA's optical measurement equipment and signal generators can achieve automated testing without the need for a computer. Users can set the equipment to provide complete signal output in four standard colors (R/G/B/W) for thorough gamma measurements. The measurements can be configured as a standard gamma curve or shown as the gamma curve and value of each tested color up to 4096 (12bit) levels.

Chroma 2238 Video Pattern Generator provides 8K Super Hi-Vision (7680x4320/8192x4320) resolutions for testing, fully supporting 8K @ 60Hz resolution. Combined with Chroma 71241 color analyzer, the test setup supports a wide luminance range (0.001 ~ 6000cd/m2) and high-precision chromaticity ≤ ±0.002 (> 0.1 cd / m2) for measurement.

Users can set the output timings and patterns on the 7'' screen of CHROMA 2238 and control the Chroma 71241 color analyzer to measure the unit under test. The test functions enable free switching between a variety of test modes that, besides gamma measurement, also include chromaticity, brightness, and flicker measurement functions. The test results are directly shown through coordinates on the CIE color space diagrams. Chroma 71241 and Chroma 2238 test setup supports program editing as well as one-click retrieval of test data through a flash drive for highly improved production efficiency.

CHROMA provides complete solutions for these and other video test applications. For more details on our products, please visit Chroma's website.