Colour Constancy Overlays

Description ↓

Colour Constancy Overlays click on the checkboxes (marked black & white, green and red) below to see the effect of the colour overlays

The red and green transparency overlays produce an approximation to full colour which is quite surprising from just red and green. Even more surprising is the blue-green you see when you overlay only the B&W and red transparencies (see notes at the foot of this page).

black & white green red

the three moving blocks are:

1. lowest layer black and white which is the reference photo converted to black and white in Photoshop using 100% on all the colour channels with the default preset.

2. middle layer green, Photoshop channel mixer to set the red channel and blue channel to zero using default preset. Then set that layer to 65% opacity.

3. top layer red. Photoshop channel mixer to set the green channel and blue channel to zero using default preset. Then set that layer to 40% opacity.

Each of these layers is saved in png format to preserve transparency.

Just checking the black & white, and red, checkboxes (i.e. no green), gives a very marked demonstration of colour constancy. The greeny-blue you see is entirely in the eye, if you colour-sample the pixels you'll find they are not green or blue, they are a dark brown or grey, but translucent 40 per cent, though that just lets through grey from the underlying black and white monochrome image.

There is a more elaborate demonstration of colour constancy on my Simulated Colour Filters page. And there is a hyphothesis about red and grey filters showing blue-green, on my page, Equivalent Colour Brightnesses.

For further examples of colour constancy see my page Colour Constancy.