Development Pages



Simulated Colour Filters
Translucent overlays to see colour constancy effects like those produced by photographing through coloured filters.
This page is inspired by Experiments in Colour Vision by Edwin Land from 1959 (Land’s paper here).
Land was not the first to demonstrate the effect of creating coloured images from black-and-white film taken through filters, In the late 19th and early 20th century there were the Biocolour process, Kinecolour and early Technicolor, all used red and green filters onto black-and-white film, re-projected through red and green filters to create something approaching full colour on screen.
Colour films made by Claude Friese-Greene in the 1920s using the Biocolour process can be seen on YouTube.
Can we simulate that on the computer monitor? On this page you select a colour photo and the code creates a greyscale image from that; it then creates three monochrome images in different colours, with translucency. Then it overlays these images which one would imagine would produce a subtractive mix – unlike projected images which form an additive mix.
The overlays do not produce a subtractive mix; it must be additive because although the amount of light is reduced with every overlay, the print process colours of cyan, magenta, yellow and black produce no better a result than red and green filters. Also intoducing the blue filter with red and green intensifies the yellows! So it is some sort of additive mix, but a rather dark one.
The colour overlays are made through the method of keeping the red, green and blue sliders in unison, there can be no brightness greater than the highest-numbered slider reaching 255, or, ignoring those that are on zero already, the lowest-numbered slider reaching zero. I also find that you really need a red or orange-red level 1 colour, and a green or cyan level 2 colour, other equally-spaced color values don’t have the same effect, though have some surprising effects nonetheless, for example in purple over black-and-white, the yellow areas of the original photo have a green look, magnified if a yellow overlay is included. These are colour constancy effects that are non-intuitive: hard to predict.
This page requires HTML5 - your browser is to old to display the page images
Brightness calculation formula:
Layer 1 (top)
Layer 2 (middle top)
Layer 3 (middle bottom)
black & white   b&w opacity %   Layer 1   Layer 2   Layer 3

Dave Collier 2020 . . . email me . . .