The colour processing that we shall be using is the subtractive method. Using the subtractive filters of yellow magenta and cyan. In practise you will only use two filters at any one time, as a third filter will simply reduce the effect of the other two.  In practise you will only use the filters magenta and yellow. …see full text PDF: Colour Printing   Min Test Strip  Print Size Exposure: Aperture – start at f8, First Test Strip: 5,10,20,40  sec, Adjust aperture to target 20  sec exposure… see full text A ring-around chart for neg/pos colour printing Filtration data shows what  to subtract from present filter settings Read more