Contrast Modulation (CM) Explained

CM is a measure of how adjacent pixels in a display distinguish themselves from one another. Technically, CM is a measure of the ability of a display to distinguish black lines and white lines on a screen.

Note that a pixel is a black line while the space between the pixels is the white line. The clarity of each is what contrast modulation is all about.

Contrast Modulation Formula

CM is calculated as a ratio or percentage of luminance using the following formula. Cm = (Lb-Lw)/(Lb+Lw) where Lb and Lw represent the luminance of black lines and white lines respectively.

The lower the Cm value less distinguishable the pixels are. Whereas, the higher the value, the more distinguishable adjacent pixels are.

Significance of Contrast Modulation

ICDM is from May 2019 onwards using CM to certify 8K Ultra HD screens. ICDM adopted contrast modulation as the ultimate true test of screen resolution in a meeting at California on May 18, 2019.

Evolution of resolution from SD, HD, UHD, 4K UHD, and now to 8K UHD was previously purely based on the number of pixels in the display. Manufacturers were required to produce screens with at least 50% contrast modulation. Therefore, screen manufacturers never paid much attention to contrast modulation.

Application of Contrast Modulation

The invention of 8K UHD caught the attention of ICDM that there is more to screen resolution than just the number of horizontal pixels as it was the case before 8K UHD. ICDM was right. Further research revealed that it was possible to have poor resolution even with more pixels.

International Committee for Display Metrology (ICDM) is the body that is mandated with the task to set metrology standards. Currently, TV manufacturers must indicate CM value of the screens they produce for approval. Previously, the CM value of 50% was just sufficient.

So far, only LG has met this regulation on their “Real 8K TV” and that was released on. Courtesy of that, LG becomes the first company to have its 8K displays certified.

 

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