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在彩色电视机中,为了重现逼真的图像及艳丽的色彩,必需传送代表背景亮度的直流分量。但这样做,在背景亮度较亮的画面中的某一个高亮度的特写部分,很可能会出现亮度饱和现象,造成图像灰度等级压缩,失掉图像柔和感并使清晰度降低。另外这种过亮的现象也会使行输出电路负载加重,成为故障的苗子。所以在彩色电视机中都设有自动亮度限制电路(ABL 电路)。本文以 X 53 P 型电路为例,说明 ABL 环路构成原理和使用国产彩色显象管时其正确工作状态的确定。
In color televisions, in order to reproduce lifelike images and gorgeous colors, it is necessary to transmit a direct current component that represents the brightness of the background. However, in a brightly colored close-up part of a picture with a brighter background, brightness saturation is likely to occur, causing the image gradation to be compressed, losing the softness of the image and degrading the sharpness. In addition this too bright phenomenon will make the line output circuit load aggravate, become the fault of seedling. So in the color TV are equipped with automatic brightness limit circuit (ABL circuit). In this paper, X 53 P-type circuit, for example, illustrates the principle of ABL loop and the use of domestic color CRT to determine the correct working state.