Chart mapping the relationship of filter colour and strength. Strongest filtration is furthest from the centre. Using combinations of filters you can change the colour of light in directions between the main ‘spokes’ — for example, choosing yellowish orange (10R + 20Y) or reddish orange (20R + 10Y). Filter values hold good for CC filters used in shooting or printing; also for the relative strengths of filters in a colour head enlarger. To make up red, green and blue use combinations of yellow, magenta and cyan filters.