学习 bit depth

bit depth用来描述图片中用来描述颜色需要的bit数。

每一个像素（pixel）都需要表示颜色的bit，这些bit越多，能够表示的颜色也就越丰富。

Every color pixel in a digital image is created through some combination of the three primary colors: red, green, and blue. Each primary color is often referred to as a "color channel" and can have any range of intensity values specified by its bit depth. The bit depth for each primary color is termed the "bits per channel." The "bits per pixel" (bpp) refers to the sum of the bits in all three color channels and represents the total colors available at each pixel. Confusion arises frequently with color images because it may be unclear whether a posted number refers to the bits per pixel or bits per channel. Using "bpp" as a suffix helps distinguish these two terms.

bits per channel，每个颜色通道的bit depth。

bits per pixel，每像素点总共的bit depth，bpp。

一般的数码相机的bpp都是24，即每个channel有 8 bit depth。

上表汇总了一些常见的名词术语。

The human eye can only discern about 10 million different colors, so saving an image in any more than 24 bpp is excessive if the only intended purpose is for viewing. On the other hand, images with more than 24 bpp are still quite useful since they hold up better under post-processing.

人眼大约只能识别1000万中颜色（已经够多了），那么bpp超过32的图片，主要是用来进行后期处理使用，并不是用来view的。

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