Bit depth is the number of bits used to store the color information of each pixel. Most images use at least 8 bits for each of the red, green and blue channels. This makes 24 bits per pixel and about 16.7 million possible colors.
Most digital cameras record raw files with a higher bit depth, usually 12 or 14 bits per channel. The extra information gives smoother tones and more room for editing before banding or other problems appear. JPEG files are limited to 8 bits per channel.
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