Duochrome

This filter was suggested by Bill, MaryLou and others at PIRC - thanks! The idea was to produce something similar to 'Ultraviolet', but with more control over the colouration. This version actually uses a completely different algorithm from 'Ultraviolet', and so the results are significantly different - generally, the colouration is stronger.

	Here they are again - my sons Lee and Jack, photographed on a recent Sunday afternoon visit to Sand Point, which is on the Bristol Channel near where we live. They have just decided to re-enact the famous 'stoning' scene from 'Monty Python's Life of Brian' and I, showing commendable pluck, photographed them before making a run for it...
	The filter dialog has two colour selectors, one marked 'Highlights', the other 'Shadows'. Broadly speaking, each image pixel will be re-coloured on a gradient between these two colours, depending upon its brightness. However, two sliders control the strength of the effect and the amount of the original colouration that's preserved.
	Generally, you should choose a light colour for the highlights and a dark one for shadows; if you do it the other way around, the image will take on a sort of 'negative' look (which may be useful on occasions). Use complementary colours, such as blue and yellow, for a dramatic effect; here I've used a deep plum colour with yellow just to demonstrate how sickly things can look if you have no taste.