Do optical WB filters improve RAW color latititude?

Started Aug 26, 2012 | Discussions thread
alanr0 Senior Member • Posts: 2,153
Sensor filters and colour accuracy

ZOIP wrote:

I may well be wrong about this and happy to be proven so, but as far as I know colour accuracy is not a product of differing degrees of exposure across the three channels but rather the cut off of colours brought about by having filters that better reject wavelengths outside their filter colour. In other words if the filters are significantly different we get better seperation and improved colour.

As I understand it, colour accuracy would not improve if crosstalk between red green and blue channels were greatly reduced. Reproduction of subtle variations in hue relies on partial overlap between colour channels.

Consider a rainbow, or preferably the spectrum of light dispersed from sunlight by a prism or diffraction grating in a darkened room. The eye perceives a continuous transition through red/orange/yellow/green/blue/violet. Suppose your camera sensor has filters with sharp transitions between red/green and green/blue. If there is no overlap between filters, then each monochromatic hue can only appear to the camera as saturated red, green or blue, with more subtle distinctions impossible.

For accurate colour reproduction, the filters should respond in a similar way to the pigments in the human retina, which show considerable spectral overlap.

In general, the match is not exact, so it can be difficult to simultaneously get good reproduction of, for example, skin tones, reds and greens, all in the same image.

Thousands of fully balanced captures that I have made have consistently produced better not worse colour and this especially applies to subtle natural shades in skin, foliage etc. Having said that one does need to do some profiling etc to get the optimal results, it is not a trivial matter but in my experience the ultimate result is better not worse colour.

Theory can point you in a good direction to experiment, but the final result - as perceived by a human eye - is what matters.

Alan Robinson

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