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Contrast refers to the measurement of different brightness levels between the brightest white and the darkest black in the bright and dark areas of an image. The larger the difference range, the greater the Contrast, and the smaller the difference range, the smaller the contrast. A good contrast ratio is 120. :1 can easily display vivid and rich colors, when the contrast ratio is as high as 300:1, it can support all levels of colors. However, the contrast ratio suffers from the same dilemma as the brightness. There is no effective and fair standard to measure the contrast ratio, so the best way to identify it is to rely on the user’s eyes.

In a dark room, the brightness in a white screen (when it is brightest) is divided by the brightness in a black screen (when it is darkest). To be more precise, the contrast is the subtraction of the saturation of the white signal at 100% and 0%, and then dividing by the 0% white value with Lux (illuminance, that is, lux, lumens per square meter) as the unit of measurement ( 0% of the white signal is actually black), the value obtained. Contrast is the division of the whitest and darkest brightness units. Therefore, the brighter the white and the darker the black, the higher the contrast. Strictly speaking, we mean the contrast ratio is the ratio of the brightness of the same point on the screen when it is the brightest (white) and the darkest (black), but usually the contrast index of the product is in terms of the entire screen, for example, a screen is completely white. The brightness of the screen is 500cd/m2 in the screen state, and the brightness is 0.5cd/m2 in the black screen state, so the contrast of the screen is 1000:1.

Visual influence
Contrast is very important for visual effects. Generally speaking, the greater the contrast, the clearer and more eye-catching the image, and the brighter the color; while the lower the contrast, the whole picture will be gray. High contrast is very helpful for image clarity, detail performance, and gray level performance. In some aspects of text display, CAD display and black and white photo display with large black and white contrast, high-contrast products have advantages in black and white contrast, sharpness, and completeness. Relatively speaking, in terms of color levels, the effect of high contrast on the image is not obvious. Contrast has a greater impact on the dynamic video display effect. Because the light-dark transition in the dynamic image is faster, the higher the contrast, the easier it is for human eyes to distinguish such a conversion process.
There are two ways to improve contrast:

  1. Increase the brightness of the white screen.
  2. Make the black darker and lower the minimum brightness. This may be a bit difficult to understand. First of all, you need to know that controlling the light and dark changes of the Liquid Crystal display is impossible to achieve by turning on and off the light-emitting tube, and the Liquid Crystal cannot be done. It is 100% without light leakage, so even if it is adjusted to a pure black screen, the LCD display will still have some brightness. This is a problem of denominator and numerator. If the denominator is smaller, the contrast will naturally increase.

The method of increasing brightness and contrast is relatively simple, but due to problems such as lamp life, liquid crystal light leakage, etc., the brightness cannot be increased infinitely. The second method is the development direction of many high-end LCD manufacturers, which is why LCDs with low brightness can achieve high contrast. When buying a liquid crystal display, you should pay attention to whether the display screen has color distortion due to high brightness, because such high contrast is of no reference value. More importantly, the falsely high brightness will not bring a better display effect, it will only turn the light-colored image into a vast area, but it will not help the performance of the dark part.

In contrast adjustment, there are also big differences in the processing methods of each product. Some products have a very small contrast adjustment range, and the adjustment process is more inclined to change the image brightness (increase the highlight area.

Lithography process contrast
It is an important indicator for evaluating image quality. It is usually obtained by dividing the difference between the maximum light intensity and the minimum light intensity of the aerial image by the sum of the two, or the difference between the maximum light density and the minimum light density of the image divided by the sum of the two The ratio, the value is between 0-1, the larger the value, the greater the difference between light and dark in the image, and the better the image contrast.

Photoresist contrast refers to the steepness of the transition from the exposed area to the non-exposed area on the photoresist. The higher the contrast, the easier it is to produce vertical photoresist sidewalls. In the imaging field, a more classic characterization index is contrast. Consider a line pattern of equal width. The light-transmitting area and opaque area of ​​this pattern have the same width. The contrast of the image of equal width line graphics is determined by the maximum and minimum imaging results. Since the goal of photolithography imaging is to present a clear image of the mask on the silicon wafer, the smaller the minimum imaging value, the greater the contrast. If the minimum value is 0, the contrast is 1.