Luminance frequency response for local dimming of LCD displays

Measuring the luminance of LCD screens with Local Dimming reveals the equivalent of a low-pass filter, whose transition frequency depends on the size of the zones. https://i.ibb.co/2F9vxDm/IMG-00001.png

A white window on a black background of 1% corresponds to an image of 288 x 288 pixels on a UHD panel. A fMAX frequency on a UHD panel corresponds to 1920 horizontal cycles of 2 pixels in size. Contrast at this frequency is limited by the panel’s native contrast ratio (1000:1 in IPS, 6000:1 in VA, 50,000:1 in Dual Layer IPS-LCD, 1,000,000:1 in OLED/µLED). A fMIN frequency on a UHD panel corresponds to 1 horizontal cycle of 3840 pixels. Local dimming therefore only acts at low frequencies.

The idea would be to link luminosity to spatial frequency to help people understand the difference between a technology such as OLED on the one hand and a mini-LED LCD on the other, so as to highlight the sudden loss of luminosity of a mini-LED when an object measuring 72 x 72 px (0.0625%), 36 x 36 px (0.015625%), 18 x 18 px (0.004%) or even less is displayed on screen on a black background. This may be the case for a simple subtitle or a specular reflection on a black background, which will not be very bright (typically less than 100 cd/m² on a black background at 0.015 cd/m² without blooming, or 150 cd/m² with slight blooming, or 250 cd/m² or more with visible blooming, or ¼ of these luminous values on IPS/ADS panels, forcing the black level up to avoid blooming), whereas the TV’s specifications would suggest otherwise (5,000 cd/m²).

This would make it possible to assign a spectral signature to each TV. https://i.ibb.co/P5GVt30/IMG-00002.png

So my question is this: Could you perform a luminance test between 100% and 0.004%? 1 %, 4 %, 10 %, 16 %, 25 %, 50 %, 64 %, 100 % = OK ¼ %, 1/16 %, 1/64 %, 1/256 % = Necessary to reveal the true nature of mini-LEDs

Ideally, you’d like to measure the white level but also the black level, as the black level tends to increase at high frequencies.

It could give this kind of curve on a TV with 10,000~100,000 zones (this is not a measurement but an estimate). https://i.ibb.co/28BmJCZ/IMG-00003.png

Thank you for reading. Thank you for your excellent tests.

Best regards.

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