What is the Difference between an HDTV's Dynamic and Static Contrast Ratio?

Contrast control refers to grasping the measurement of different brightness levels between the brightest white and the darkest black in the image. The larger the difference range, the larger the contrast, and the smaller the difference range, the smaller the contrast.

The CCD camera used by the CCD camera generally has a large dynamic range, which enables the CCD camera to adapt to high-contrast shooting environments. Dynamic Contrast Control (DCC-Dynamieeontrasteontrol) is a technology that uses the characteristics of the large dynamic range of a CCD camera to enable the CCD camera to obtain high-quality color images under high-contrast shooting conditions (including shooting objects with high contrast).

The range of contrast performance that an ordinary CCD camera system can achieve is determined by two factors: First, in order to ensure that the dark part of the image has a sufficiently high signal-to-noise ratio, the noise level determines the darkest area in the reproducible scene. Second, the maximum video signal peak of the PAL system is 700mv. If this camera is used in a shooting environment with a high contrast, when the video level exceeds the above-mentioned two-level limit, the quality of its reproduced image will be affected by the decrease in contrast expressiveness. For example, when the camera is aimed at a bright scene outside the window for shooting, because the light levels inside and outside the window are different, the image details outside the window will not be reproduced normally on the image monitor due to its high video level. ^[1]

The related problems of establishing a four-mirror ring-shaped feedback system are discussed, and the principle of changing the ratio when using the ring-shaped feedback system to control the image is discussed. ^[2]

How contrast control works

Suppose that the input is an irregularly arranged multi-gray scale transparent sheet, in which every two transmittances can form a contrast C. If A _{1 is} fixed and A _{2 is} changed, a set of discrete values of the input contrast C can be obtained. Let a and be fixed, then we know that the corresponding output C will change non-linearly. Now adjust the regulated variable power supply to cause displacement deformation of the piezoelectric crystal connected to M ₃ and further change , then the change of the output contrast C corresponding to different formazan, if A _{1 is} taken Through all the transmittance values in the input, the contrast changes of all C values after the system is processed can be clear. Part of the calculation result curve during the analysis, the rest can be reasoned by the same reason.

When A ₁ = 0.08 and a = 0.75, the relationship between C and C can be obtained. The dashed line is a curve with zero change in the output contrast, and it represents the input contrast curve. When A ₁ = 0.3 and a = 0.75, the relationship between C and C is obtained.

Analysis of analytical formulas and curves can be concluded:

Compared with the input contrast, when = 0 ° , the output contrast increases the most, and when = 180 ° , the output contrast decreases the most. ^[2]

a Effect of contrast control loss coefficient a on coefficient processing ability

The analysis performed under the condition that a is a fixed value, when a changes, feedback changes in the processing capacity of the system. From the analysis, it can be seen that when = 0 ° or = 180 ° , the output contrast increases or decreases as an extreme value. Now is fixed at 0 ° or 180 ° , and the change of the output contrast when a is changed is analyzed. When is another fixed value, the influence of a on the processing capacity of the system can be reasoned by the same reasoning.

Also set A ₁ = 0.01, which is a fixed value, then when = 0 ° and a is a variable value, the relationship between input and output can be obtained. When = 180 ° and a is a variable value, another set of relationship curves between input and output can be obtained, see ₃ and ₄ . When A ₁ = 0.3, the contrast relationship curve when a is changed can be obtained.

Analyzing the contrast relationship curve when a changes, it can be seen that compared with the input contrast, when = 0 ° , the output contrast increases with the increase of a, and when = 180 ° , the output contrast decreases As the a increases, the amplitude also increases, that is, the larger the a, the larger the dynamic range of output contrast changes, that is, the stronger the system's ability to handle contrast changes. When A ₁ has other fixed values, the same conclusion can be drawn. In order to obtain a large a value, the r value of the high mirror and the transmittance of the Fourier transform objective lens can be increased as much as possible. For the value of r ₁ , it should be selected through experiments to ensure that the system has sufficient output light energy to observe and take pictures, and has strong processing ability. ^[2]