Even Higher Bit Depths?


Today’s Question: You answered a question about the 32-bit per channel option but suggested that 16-bit was the most a photographer would realistically need. But my flatbed scanner claims to have a bit depth of 48-bit. Is that just marketing hype, or is there actually some benefit to this higher bit depth?

Tim’s Quick Answer: Actually, in this case the confusion comes from how the information is being presented. A bit depth of 48-bits for the scanner is the same thing as 16-bits per channel for an RGB image.

More Detail: Bit depth can understandably be a somewhat confusing topic, especially because the numbers involved can get rather big rather quickly.

Bit depth is typically described as a number of bits per channel, such as 8-bits or 16-bits per channel. Most photographers are dealing with RGB (red, green, blue) images, which have three channels.

So, if you are able to scan at a bit depth of 16-bits per channel, that is the same as 48-bit (without “per channel” on the end of it). If you have 16 bits for the red channel, 16 bits for the blue channel, and 16 bits for the green channel, that adds up to a total of 48 bits (16+16+16=48).

Similarly, you may sometimes see a bit depth presented as 24-bit, which would indicate a bit depth of 8-bits per channel for an RGB image (8+8+8=24). The key thing to keep in mind is that if you don’t see “per channel” after the indication of bit depth then you likely need to divide the number by three to determine the actual per-channel bit depth, assuming of course that the information presented was based on an RGB image.