To combine with an original during the printing of a separation negative or positive.

In this case, the mask is used to produce a separation image that matches the other two separation images in contrast. The process is used for the restoration of faded negatives or positives where one dye is more faded that the others. The mask is made on black and white panchromatic film by printing the original with colour light of the colour to be restored. A faded cyan dye on a negative requires a black and white mask made through a red filter. The resulting positive mask is printed to make a negative mask, the mask and the original combined in register to make the corrected red separation positive.

This process is extremely rarely performed, it is costly, time consuming, and requires a technician capable of matching the resulting separation contrasts. Considerable technical understanding of the process is essential to calculate the process gammas required. This makes the procedure one that will only be carried out as a last resort in organisations that specialise in colour film restoration.

This process can correct faded colour film when one or more dyes are virtually undetectable to the eye. Similar but less correction can also be produced by varying the development contrast of the separation image. This is explained in Colour Duplication chapter [cv].