What is subtractive colour?
Subtractive systems involve coloured dyes or filters that absorb power from selected regions of the spectrum. The three filters are placed in tandem. A dye that appears cyan absobs longwave (red) light. By controlling the amount of cyan dye (or ink), you modulate the amount of red in the image. In physical terms the spectral transmission curves of the colourants multiply, so this method of colour reproduction should really be called “multiplicative”. Photographers and printers have for decades measured transmission in base-10 logarithmic density units, where transmission of unity corresponds to a density of 0, transmission of 0.1 corresponds to a density of 1, transmission of 0.01 corresponds to a density of 2 and so on. When a printer or photographer computes the effect of filters in tandem, he subtracts density values instead of multiplying transmission values, so he calls the system subtractive. To achieve a wide range of colours in a subtractive system requires filters that appear
