Why a photo scanner doesn’t need white balance

Your digital camera needs to be white balanced — actually, grey balanced would be more accurate. The reason is that the camera’s whites, greys and blacks, should all be calibrated to a known neutral value. From there, the camera’s electronics can figure out how other colors should be rendered. Photo scanners don’t have that problem.

A digital camera is used under multiple, different light conditions. It may be used in a studio, but also under sun light, in cloudy weather, etc. This makes it virtually impossible to calibrate a camera for all known colours, the way you can calibrate a printer by measuring colour patches and creating a colour profile.

Instead, all you can do with a camera is ensuring it “sees” white, grey and black the way it’s supposed to look, and then take other colours from there. Unless you’re in a studio with lighting you know the colour temperature of.

A photo scanner doesn’t need white balancing, but instead very much works like a printer. It can be calibrated by using a full-colour target and creating a colour profile for the scanner. The reason is simple: the scanner lamp has a fixed and known colour temperature and this value will not change over time — well, until the lamp starts wearing so much the scanner becomes unusable.

Because all parameters are known it doesn’t make sense to only measure white balance. With a scanner it makes sense to create a full colour profile, and that makes the scanner more colour-accurate than an ordinary digital camera.

The scanner may be more accurate, but the colours will not, because the great unknown here will be the film, and that in turn is why scanner apps like SilverFast offer so much in terms of colour correction.

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