Brought to you in cooperation with the Musée des arts et métiers - Paris.

The Phenakistiscope is a disk that turns freely around its own center. An observer must turn the disk at sufficient speed while observing images on the disk through a slit. This procedure results in an animated image, repeating itself in loop fashion, appearing on the other side of the slit. The Belgian  physicist Joseph Plateau,  born in 1803, is often credited with the invention of this ancestor of  motion pictures.
Photo credits: Musée des Arts et Metiers, Paris, 2008.

The Flash9 plugin is necessary for this animation !
Since the 1890s, additive color processes have been used to create color photographs. The cones that carpet our retinas are only sensitive to  the primary colors: Green, Red and Blue. Television, cinema and photography all use these additive, three  color processes, as did the pointillist painters of the 19th Century.

Light has to enter the eye in sufficient amounts in order for us to see. Alhazen, the Persian scientist of the 11th century, was the first to propose  this theory. Before him, there were many other theories, including ones that held that something was emitted by the eye to interact with objects being observed.

To see, enough light must go into the eye.
In general, light propagates from the source to the object and then from the object to the eye. The objects that are seen in this way are secondary sources. In contrast, the light bulb that illuminates the scene is a primary source.

An illustration of light dispersion (separation of light into component colors) through a prism. One of the most important properties  of L.A.S.E.R light is illustrated here: It is  monochromatic light (it has a very narrow frequency spectrum).

On a color monitor each group of phosphor dots is made up of one green, one blue and one red dot (RGB). By varying the brightness of each of these primary colours, color monitors can create an unlimited number of colors.

The eye merely transmits light signals to the brain which then interprets them through a series of complex operations. It may misinterpret them, in which case an optical illusion occurs. Such illusions may, like mirages, originate naturally or be induced artificially by causing what appears to be a distortion on a test element, for example by drawing arrows on straight parallel lines.

Optical illusions reveal some of the ways our brain functions.

A real example of subtractive color. You can select different filters by clicking on them, and observe their effects by rolling  them over the photo.
Primary color filters only allow their own color to pass. Secondary color filters allow two primary colors to pass.

This animation demonstrates both additive and subtractive color. Select  a color first – the roller will paint this on the screen. Then select a filter through which the screen is to be viewed.

Substractive color mixing. The three primary subtractive colors are cyan, magenta, and yellow. By mixing these, you can produce red, green and blue.