This voltage-to- light CRT transfer function is characterized by the formula output-luminance transfer function that is nonlinear. The CRT electron guns in analog CRT displays have an inherent input-voltage vs. Informally and historically, the relationship has been known as display gamma (symbol γ). This relationship between each of a display’s pixel input values and its luminance values is formally known as the display’s electrical to optical transfer function (EOTF). However, for the display technologies mentioned above, the values of all the other pixels in the frame have a dynamic effect on the relationship between a particular pixel value at the display’s input and the resulting luminance that the display produces at that pixel position. These displays include plasma panels with ABL, LCDs and PDPs with global and local dimming, and projectors with auto iris.įor many displays, there is a static relationship between a particular pixel value at the display’s input and the resulting luminance that the display produces at that pixel position.
Many display technologies dynamically adjust the luminance levels of the display, depending upon the average picture level (APL) of the currently displayed image. We present an innovative method of maintaining constant APL at any desired window size or APL, as well as constant chromatic, to maintain accurate gamma measurements not only for grayscale levels, but for all colors. We then present a type of test pattern that maintains a constant APL, despite changes to its measurement stimulus level. We also examine the latest standard for measuring the gamma performance of these displays with dynamic luminance levels. We see how a display’s gamma measurement and/or adjustment is complicated by dynamic luminance changes that are based on average picture level. We examine how a display’s gamma is specified and how it is normally measured. This report examines the gamma relationship between a display’s pixel input values and its luminance output values. This dynamic luminance adjustment complicates the accurate characterization or adjustment of gamma for these displays. Many displays dynamically adjust their luminance levels based not only on individual pixel stimulus levels, but also on the average picture level (APL) of an entire frame.
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