Color II

Classification of Colors The eye detects 3 primary colors. The color sensitive cells are the cones. there are 3 distinct types of cones. They have a peak sensitivity at wavelengths of: 477 nm blue 540 nm green 577 nm 'red' actually more yellow The brain calculates ratios from the 3 types of cones. Reminder: spectrum of visible light Monochromatic or spectral light consists of only one wavelength. e.g., = 600 nm is "Orange chrome" or "Cadmium red orange" Intensity distribution Curve. here: Solid line: the intensity of light, at each visible wavelength, obtained when white light is reflected from a greenish surface. Dashed line the same light with a little extra of red light mixed in. Although in the above curve there is a predominance of green light, there is also a little bit of every other visible wavelength present. Thus, Most colors consist of a distribution of wavelengths. When on simultaneously plays two different notes on a piano, one usually hears the two separate notes. But when two different wavelengths of light shine on the same place on a screen, the eye does not separate the resulting light into two colors, rather ones sees some sort of mixture. We need to characterize the sensations of these mixtures. Hue corresponds to the main color or color name. Hue is what distinguishes one spectral color from another. Example: all yellows differ in hue from all blues, regardless of any other possible similarity. Hue is specified by the dominant wavelength in an intensity distribution curve. Thus, the greatest intensities in the above curve lie between 500 and 530 nm, so the hue of that light is some sort of green. Note: Artists use the terms chroma or intensity to express something similar to saturation. Saturation corresponds to the purity of the color. A very saturated color generally has almost all its intensity fairly close to the dominant wavelength, while an unsaturated color would have contributions from any other wavelengths. The monochromatic, spectral colors have the highest saturation. An example of a blue color is given below: White light , which consists of all wavelengths with no dominant one, is completely unsaturated. Other colors may be thought of as mixture of white light with a saturated color. Saturation: White light is completely unsaturated. A saturated red light. A less saturated red light - pink. Brightness: Brightness of a light. The intensity distribution curves for three different brightnesses. Lightness of a surface. The curves correspond to the percentage of incident light reflected at each wavelength. Brightness refers to the sensation of overall intensity of a light, ranking from dark, through dim, to bright, and dazzling. Brightness:Intensity of Light Lightness is related tot he percentage of incident light reflected by a surface and refers to the blackness, grayness or whiteness of a color. Lightness:Percentage of incident light reflected by surface We know how to change the brightness of a light (even a colored one), we need to adjust the intensity of the source. To change the lightness of a surface one must make it less reflecting. We often think of lightness as being related to the total amount of light reflected at all visible wavelengths, but we must be careful. We can change the amount of reflected light in two ways. One is to make the surface less reflecting, the other is to change the overall illumination, the incident light. But if you shine less light on a piece of white paper, it does not appear gray, it continues to look white. That is, the lightness of any surface is nearly independent of the overall illumination. Try it! Surface reflections and saturation. Colors may be arranged according to their hue, saturation, and lightness in a color tree The `trunk' of the tree consists of the completely unsaturated colors, it ranges from black at the bottom, through grays, to white at the top. That is the height is a measure of lightness. Our from the trunk, one finds different hues in different directions, the hue varies around the tree. Finally, as one moves away from the trunk in some direction, the color becomes more saturated This scheme is realized in the Munsell Color Tree, where colors are organized by hue, saturation and lightness.

Ch. Elster
Aug 26 14:27:03 EDT 2019