Systemaufbau und Komponenten

A rugged camera stand carries the LCD monitor on which the samples to be measured are placed and provides continuous adjustment of the working distance of an electronic camera with a b/w sensor. For measurements of scattering and reflectance, a linear lamp is integrated in the optical head behind a slit with a width of 1 mm. Display monitor and sample sheets are placed on the base plate of the stand. The monitor or other display devices can be fixed with commercially available mounting clamps. Thread holes are provided in the base plate. 

The Device Under Test is typically a combination of a monitor and a cover glass. Usually the same monitor is used for evaluation of series of cover glass samples.  

Since the sparkle effect is significantly influenced by the pixel geometry of the monitor, the measurement system can optionally be delivered with specific monitor types according to the application. The pixel shape and size are the determining parameters (please specify). On the other hand any monitor can be used, that can be placed horizontally on the base plate of the stand. The monitor can be exchanged for different applications.

With optional motorized shifting stage the sample can automatically be shifted during the measurement of sparkle. Thus this measurement can be fully automated and does not need operator's interaction during image capturing. At the same time this stage can be adjusted to the sample size (width) and thus facilitates the placement of the sample to the correct position. The stage also works with series of samples with different sizes, if the sample is aligned with one side of the sample holder at the beginning of the measurement.


The system is delivered with a software package that automates the

measurements (depending on the equipment) and the evaluation of the

images. The picture at the right shows a sample dialog for sparkle measurement.

Measurement method for sparkle: Image difference. The difference of two images with shifted DUT is evaluated by the statistical figures of the grey-level distribution:
s =  σ / μ   sparkle value 
The magnification of the optical system can be varied in the range of appr. 5 - 25 camera pixels (cpx) per display pixel (dpx), with typical settings of 10 cpx / dpx. The working distance can be varied between appr. 100 mm and 700 mm, with typical values of 500 mm. The measurement setup reproduces the actual application situation: 

 -         LCD-monitor with a glossy screen as light-source
 -         Test samples: AG treated glass sheets on top

Best results are typically achieved with monochromatic green monitor image. However the color can be varied according to the application and requirements.


Illumination: linear light source (CCFL). 

The intensity of reflected light is recorded as a function of the location on the display.

The shape of the intensity curve describes the scattering characteristics of the AG-layer. 

Anti-reflection factor:
AR = max(LAG) / max(LLCD) < 1

The scattering of the AG layer effects a low-pass filtering (blurring), the Distinctness of Image (DOI) is reduced. 

Glossy display without surface treatment (right) and with AG coated glass (left). The image of the pixel array gets blurred. 

Luminance modulation obtained from the figure above.

Red: without AG layer,
blue: with AG-layer.  

The scattering AG-layer reduces the amplitude and attenuates high-frequencycomponents (smoothing). A measure for the distinctness or blurring of an image is the Modulation Transfer Function (MTF):