Slide Scanning: Part 3—Colour Depth
In scanning my slides, the next setting I needed to think about was the bit depth for the colour. The scanning software from Epson basically allows the colour depth choice of 24-bit or 48-bit. With 24-bit this allows for 8 bits for each of the RGB colour channels.
With 8 bits a channel that permits 2**8 (2 to the power 8) shades of colour per channel—which is 256 shades per the red, green, and blue channels. This number of shades per channel allows for a total of 16,777,216 colours (being 256 to the power 3).
Selecting a 48-bit colour depth allows for 16 bits per RGB colour channel. This gives you 2**16 (2 to the power 16) shades of colour per channel—which is 65,536. With 65,536 shades per channel then a total of around 280 trillion colours is available (being 65,536 to the power 3).
If you do some research on the Internet you will find that the effective colour depth provided by the emulsion used on slide film is considered to be around 12 bits per channel (it varies slightly per emulsion type), which suggests that slide film can capture about 68 billion different colours.
This being the case, using 48-bit scanning—which allows for 280 trillion colours—should be able to pretty much represent the 68 billion possible colours on a slide.