LMK Display Sparkle

Display uniformity is an essential quality criterion for modern displays. This also applies for high frequency non-uniformities as OLEDs sandy Mura or anti-glare-layer (AGL) caused display sparkle. In 2019 TechnoTeam and two major companies from the automotive industry started a joint venture to measure anti-glare layer display sparkle. There we identified the following requirements:

• Measurements with BlackMURA compliant equipment and setup
• Measurements without the need to remove the Anti-Glare-Layer
• High correlation to human perception

Meanwhile, our sparkle measurement solution has been applied to display specifications of major automotive companies. Our sparkle AddOn can be used with all LMK5 and LMK6 cameras and all standard lenses starting from 16 mm focal length.

Sparkle measurement setup table for different (BlackMURA complaint) LMK systems

Starting from an initial distance according to the available camera and lens (see table), the alignment procedure is identical to that of BlackMura. Our camera's live view mode allows an easy and comfortable alignment. This includes the measurement of the sparkle-relevant setup parameters “angular aperture” given in degrees and the “optical magnification” given in camera pixels per mm. The only difference to a BlackMURA measurement is, that the lens focus needs to be adjusted directly to the display (within Moiré). After this, a full green image is shown to evaluate the sparkle and an image is captured. The impacts of Moiré, pixel structures or dusts and pixel defects are corrected by our frequency-filter based algorithm. While the default evaluation is set to automotive viewing distances, it can also be adapted to other viewing distances. Via the innovative frequency-downscaling we can correct for different magnifications, which leads to an outstanding ratio between reproducibility and the flexibility of the setups.

As sparkle values are very sensitive to the focus setting (blurring sparkle can be very critical), we developed the distance-focus-scan. Using this method all LMKs (especially manual focus lenses) can be used to search for the maximum, where we have the sharpest image of the sparkle. This significantly improves reproducibility and also ensures that we evaluate the worst case sparkle that a human can observe in the sample. All that is required is a simple motorized linear axis, which can be ordered together with the sparkle add-on. Of course the add-on also allows to use external (even manual) stages. Alternatively, a LMK Positon system can be used as well.

Typical curve of a distance-focus sparkle scan from LabSoft.