Why a photo scanner can be fully colour balanced

Ever wondered why a scanner can be colour calibrated and a digital camera can’t? Your digital camera needs to be white balanced at the least. The reason is that the way the camera ‘sees’ grey should be calibrated to a known neutral value. From there, you can rely on the camera ‘knowing’ how other colors should be rendered. For best accuracy, a camera should be fully colour calibrated, just like  a scanner. But in practice, this is near-impossible.

You use your digital camera under different lighting conditions. One moment, you’re in bright sun light, the next clouds make for a grey mess. This makes it virtually impossible to calibrate a camera for all known colours. What you theoretically should do is make a profile for every slight change in colour temperature — whenever the light changes even a little bit — and that is simply not feasible.

Instead, what you can do is ensuring the camera “sees” white, grey and black the way it’s supposed to look, and then correct the minor colour casts that are inevitable, in software. Only in a studio with lighting you know the colour temperature of can you create a full blown colour target for your camera. Even then, it’s difficult to do so because you need to make sure the colour target is shot with as even lighting as possible, under ideal circumstances (no stray light, etc, etc).

A photo scanner is easier: it can be calibrated by using a full-colour target and creating a colour profile for the scanner because 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 anyway.

With a scanner it makes sense to create a full colour profile. The element of uncertainty becomes the film or print you’re about to scan. And that  is why scanner apps like SilverFast offer so much in terms of colour correction. Of course, you could do such editing in Photoshop, well after you’ve scanned your photos, but SilverFast offers a huge benefit: it allows you to edit one photo and batch process all the others.

So, if you have a negative film and you correct one photo of that film, all other photos will require the same corrections. Batch processing then saves you a lot of time.

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