How many bits of data does a digital camera sensor actually capture?
Asked 5/6/2011
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I’ve seen claims that camera sensors typically output only 12–14 bits, which seems low compared with 24-bit RGB images. Is that 12–14 bits per pixel or per color channel? How do digital camera sensors usually encode their data, especially in RAW files versus final RGB images?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
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The photosites of a digital sensor are actually analog devices. They don't really have a bit depth at all. However, in order to form a digital image, an analog-to-digital converter (A/D converter) samples the analog signal at a given bit depth. This is normally advertised in the specs of a camera — for example, the Nikon D300 has a 14-bit A/D converter.
But keep in mind that this is per channel, whereas 24-bit color usually means 8 bits per channel. Some file formats — and working spaces — use 16 bits per channel instead (for 48 bits total), and some use even more than that.
This is partly so the extra precision can reduce accumulated rounding errors (as you note in your question), but it's also because human vision isn't linear, and so the color spaces we use tend to not be either. Switching from a linear to "gamma compressed" curve is is a lossy operation (see one of the several questions about raw files), so having more bits simply means less loss, which is better if you change your mind about exposure/curves and don't have access to the RAW file anymore.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
15y ago
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Generated from our catalog & community — verify before relying on it.
A camera sensor itself is analog; the bit depth comes from the camera’s analog-to-digital converter (ADC). In practice, many cameras digitize sensor data at about 10–14 bits per sampled value, with 12–14 bits being common.
That is usually per component/sample, not per finished RGB pixel. Most sensors use a Bayer pattern, where each photosite records only one color value (red, green, or blue). So a RAW file typically stores one 12–14 bit value per photosite. Later, demosaicing interpolates the missing two color channels for each pixel from neighboring samples.
This is why “24-bit color” is not a contradiction: 24-bit RGB usually means 8 bits each for red, green, and blue in the final image, while RAW capture may start from 12–14 bits per sensor sample. Higher internal bit depth helps preserve tonal precision and editing latitude before the image is converted to an output format.
Also, usable bit depth is limited by noise, so not every recorded low-order bit represents meaningful image information.
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