Colour Basics: How cameras see colour.

I have decided instead to serialise what was planned to be a very large tutorial on colour, and this is the first of these which will look at how film and camera sensors interpret colour.

How digital sensor’s see colour:

You might not know that a sensor does not natively record colour, and that digital sensors record light by increasing the amount of light in the image into a series of microlenses, which then filter into a pixel for each micro lens, each pixel can only however record the amount of light it receives in black and white.

The way a colour image is created from these pixels is through three channels, for Red, Green and Blue. Each pixel is filtered to only record from one of these and the pixels are aligned in the Bayer interpolation. The Bayer interpolation is an arrangement of the pixels to give even distribution of colour, it is the most commonly used arrangement and features in most DSLRs.
The Bayer interpolation, photo courtesy of Wikipedia

How films see colour:

Films interpret colour chemically and depending on the type of film either darkens (Negative/ Print film) or brightens (Reversal/ Slide Film) under light. Film also divides into three colour channels. This is done through the use of emulsion layers, which are layers which are sensitive to a certain colour of light, with intermittent filters which block the already received colours.
Emulsion layers, courtesy of How are they different?

There are a variety of differences in the subtleties of how these two methods interpret hues, and there are of course the physical advantages, digital being able to take almost limitless photos with the single sensor, whilst film is relatively immune to sensor dust from shot to shot. Some of the more noticeable differences however are the digital sensor’s “clipping” white highlights, the result of a pixel filling with light and effectively overloading and spilling over to it’s neighboring pixels, this is especially noticeable with CCD sensors (Now less common then the CMOS sensors used in most modern DSLRs). The other key difference is that whilst light from any angle is absorbed directly down through emulsion layers, light hitting the microlenses of a digital sensor from a wide angle lens run the risk of penetrating neighboring pixels of other colours, resulting in chromatic aberration. Below is a diagram of this.
This one is by me, you can probably tell..

Further Reading:

The process is quite simply and understandably demonstrated in Photojojo’s tutorial on how to create a colour image using black and white photographs and coloured filters.


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