Chroma: How pure a hue is in relation to gray Saturation: The degree of purity of a hue. Intensity: The brightness or dullness of a hue. One may lower the intensity by adding white or black. Luminance / Value: A measure of the amount of light reflected from a hue. Those hues with a high content of white have a higher luminance or value. Shade and tint are terms that refer to a variation of a hue.
This powerful optical illusion, created digitally by R. Beau Lotto, is called the cross-piece illusion. Two bars made up of colored cylinders, meet in a junction piece. In one picture, the cross-piece looks blue-gray. In another it looks yellow. In fact it’s precisely the same color. View the illiusion with a slider here: http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html #colour #illusion
Another famous illusion, this one was recently rediscovered in a cafe wall at the bottom of St. Michael’s Hill. Although the lines appear to be diverging from one another they are in fact quite parallel.