Introducing Colour For Print
http://en.wikipedia.org/wiki/Color
http://en.wikipedia.org/wiki/Subtractive_color
http://en.wikipedia.org/wiki/Additive_color
http://en.wikipedia.org/wiki/Gamut
http://dx.aip.org/advisor/cmyk_color.html
Color or colour (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, green, blue, and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates.
Because perception of color stems from the varying spectral sensitivity of different types of cone cellsin the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully explain the psychophysical perception of color appearance.
The science of color is sometimes called chromatics, chromatography, colorimetry, or simply color science. It includes the perception of color by the human eye and brain, the origin of color in materials,color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light).
Electromagnetic radiation is characterized by its wavelength (or frequency) and itsintensity. When the wavelength is within the visible spectrum (the range of wavelengths humans can perceive, approximately from 390 nm to 750 nm), it is known as "visible light".
Most light sources emit light at many different wavelengths; a source's spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, there are many more possible spectral combinations than color sensations. In fact, one may formally define a color as a class of spectra that give rise to the same color sensation, although such classes would vary widely among different species, and to a lesser extent among individuals within the same species. In each such class the members are called metamers of the color in question.
- The eye contains two kinds of receptors: rods and cones.
- While the rods convey shades of grey, the cones allow the brain to perceive colours .
- Of the three types of cones, the first is sensitive to red-orange light, the second to green light and the third to blue-violet light.
When a single cone is stimulated, the brain perceives the corresponding colour:
If our green cones are stimulated, we see "green".
If our red-orange cones are stimulated, we see "red".
If both our green and red-orange cones are simultaneously stimulated, our perception is yellow.
Additive color describes the situation where color is created by mixing the visible light emitted from differently colored light sources. This is in contrast to subtractive colors where light is removed from various part of the visible spectrum to create colors. Computer monitors and televisions are the most common form of additive light, while subtractive color is used in paints and pigments and color filters. The additive reproduction process usually uses red,green and blue light to produce the other colors. Combining one of these additive primary colors with another in equal amounts produces the additive secondary colors cyan, magenta, and yellow. The colored pixels in displays do not overlap on the screen, but when viewed from a sufficient distance, the light from the pixels diffuses to overlap on the retina. Another common use of additive light is the projected light used in theatrical lighting, such as plays, concerts, circus shows, and night clubs.[1] Every possible combination of luminosoties of each light (color) is equal to the fullgamut of those three lights (colors).
All work should be in the CMYK (Cyan/Magenta/Yellow/Black) mode, as this is the mode required for the printing process. If an RGB (Red/Green/Blue) file is submitted, it must be converted to CMYK. When the conversion takes place, color shifts can occur and TSG will do our best to reproduce as close of a match to your printed output as possible.
Color or colour (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, green, blue, and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates.
Because perception of color stems from the varying spectral sensitivity of different types of cone cellsin the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully explain the psychophysical perception of color appearance.
The science of color is sometimes called chromatics, chromatography, colorimetry, or simply color science. It includes the perception of color by the human eye and brain, the origin of color in materials,color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light).
Electromagnetic radiation is characterized by its wavelength (or frequency) and itsintensity. When the wavelength is within the visible spectrum (the range of wavelengths humans can perceive, approximately from 390 nm to 750 nm), it is known as "visible light".
Most light sources emit light at many different wavelengths; a source's spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, there are many more possible spectral combinations than color sensations. In fact, one may formally define a color as a class of spectra that give rise to the same color sensation, although such classes would vary widely among different species, and to a lesser extent among individuals within the same species. In each such class the members are called metamers of the color in question.
- The eye contains two kinds of receptors: rods and cones.
- While the rods convey shades of grey, the cones allow the brain to perceive colours .
- Of the three types of cones, the first is sensitive to red-orange light, the second to green light and the third to blue-violet light.
If our green cones are stimulated, we see "green".
If our red-orange cones are stimulated, we see "red".
If both our green and red-orange cones are simultaneously stimulated, our perception is yellow.
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| SUBTRACTIVE COLOUR |
A subtractive color model explains the mixing of paints, dyes, inks, and natural colorants to create a full range of colors, each caused by subtracting (that is, absorbing) some wavelengths of light and reflecting the others. The color that a surface displays depends on which colors of the electromagnetic spectrum are reflected by it and therefore made visible.
Subtractive color systems start with light, presumably white light. Colored inks, paints, or filters between the viewer and the light source or reflective surface subtract wavelengths from the light, giving it color. If the incident light is other than white, our visual mechanisms are able to compensate well, but not perfectly, often giving a flawed impression of the "true" color of the surface.
Subtractive color systems start with light, presumably white light. Colored inks, paints, or filters between the viewer and the light source or reflective surface subtract wavelengths from the light, giving it color. If the incident light is other than white, our visual mechanisms are able to compensate well, but not perfectly, often giving a flawed impression of the "true" color of the surface.
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| ADDITIVE COLOUR |
Additive color describes the situation where color is created by mixing the visible light emitted from differently colored light sources. This is in contrast to subtractive colors where light is removed from various part of the visible spectrum to create colors. Computer monitors and televisions are the most common form of additive light, while subtractive color is used in paints and pigments and color filters. The additive reproduction process usually uses red,green and blue light to produce the other colors. Combining one of these additive primary colors with another in equal amounts produces the additive secondary colors cyan, magenta, and yellow. The colored pixels in displays do not overlap on the screen, but when viewed from a sufficient distance, the light from the pixels diffuses to overlap on the retina. Another common use of additive light is the projected light used in theatrical lighting, such as plays, concerts, circus shows, and night clubs.[1] Every possible combination of luminosoties of each light (color) is equal to the fullgamut of those three lights (colors).
Colour Gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut, is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device. Another sense, less frequently used but not less correct, refers to the complete set of colors found within an image at a given time. In this context, digitizing a photograph, converting a digitized image to a different color space, or outputting it to a given medium using a certain output device generally alters its gamut, in the sense that some of the colors in the original are lost in the process.
Computer monitors emit color as RGB (red, green, blue) light. Although all colors of the visible spectrum can be produced by merging red, green and blue light, monitors are capable of displaying only a limited gamut (i.e., range) of the visible spectrum.
Whereas monitors emit light, inked paper absorbs or reflects specific wavelengths. Cyan, magenta and yellow pigments serve as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colors. Like monitors, printing inks also produce a color gamut that is only a subset of the visible spectrum, although the range is not the same for both. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. Also, because printing processes such as offset lithography use CMYK (cyan, magenta, yellow, black) inks, digital art must be created as CMYK color or must be converted from RGB color to enable use.
It can sometimes be difficult to visualize the reason for color shift in color space conversion. The best way to see the color differences between the CMYK and RGB color spaces is to look at a color gamut comparison chart. The chart to the left plots the visible color spectrum as the large "horse shoe" area, and within this is a plot of the CMYK colors, and the RGB colors. You can see that in some areas the RGB color space is "outside" that of the CMYK space. It is these colors that will be affected by a conversion from RGB to CMYK.
