User:Krispy Treat/Temp

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The HSV (Hue, Saturation, Value) model, also known as HSB (Hue, Saturation, Brightness) or hexcone model, defines a color space in terms of three constituent components:

• Hue, the gradation of color
• Saturation, the departure from achromaticity
• Value, the departure from black, the color of zero energy

The HSV model was created in 1978 by Alvy Ray Smith in an attempt to better capture the artistic ideas of hue, tint, shade, and tone. It is a nonlinear transformation of the RGB color space, and may be used in color progressions. Note that HSV and HSB are the same, but HSL is different.

[edit] Components

[edit] Hue

Main article: Hue

Hue ranges from 0° (red) through 60° (yellow), 120° (green), 180° (cyan), 240° (blue), 300° (magenta), and back to 0°. It specifies the dominant wavelength of the color, except for the blue-magenta-red region (between 240° and 360°) where it denotes a position along the line of pure purples. Red, Chestnut, and Falu red are all shades of red with a hue of 0°. The hue of achromatic color is undefined.

[edit] Saturation

Main article: Saturation (color theory)

Saturation ranges from 0 (fully desaturated) to 1 (fully saturated). A desaturated color is achromatic, with undefined hue.

[edit] Value

Main article: Brightness

Value ranges from 0 (black) to 1 (white). A devalued color is black, with undefined hue and saturation.

[edit] Visualization

An HSV color wheel allows the user to quickly select a multitude of colors.

Time-varied representation of the HSV color wheel.

The HSV model is commonly used in computer graphics applications. In various application contexts, a user must choose a color to be applied to a particular graphical element. When used in this way, the HSV color wheel is often used. In it, the hue is represented by a circular region; a separate triangular region may be used to represent saturation and value. Typically, the vertical axis of the triangle indicates saturation, while the horizontal axis corresponds to value. In this way, a color can be chosen by first picking the hue from the circular region, then selecting the desired saturation and value from the triangular region.

The conical representation of the HSV model is well-suited to visualizing the entire HSV color space in a single object.

Time-varied representation of the HSV cone.

Another visualization method of the HSV model is the cone. In this representation, the hue is depicted as a three-dimensional conical formation of the color wheel. The saturation is represented by the distance from the center of a circular cross-section of the cone, and the value is the distance from the pointed end of the cone. Some representations use a hexagonal cone, or hexcone, instead of a circular cone. This method is well-suited to visualizing the entire HSV color space in a single object; however, due to its three-dimensional nature, it is not well-suited to color selection in two-dimensional computer interfaces.

The cylindrical representaion of the HSV model might be considered the most mathematically accurate model of the HSV color space.

Time-varied representation of the HSV cylinder.

The HSV color space could also be visualized as a cylindrical object; similar to the cone above, the hue varies along the outer circumference of a cylinder, with saturation again varying with distance from the center of a circular cross-section. Value again varies from top to bottom. Such a representation might be considered the most mathematically accurate model of the HSV color space; however, in practice the number of visually distinct saturation levels and hues decreases as the value approaches black. Additionally, computers typically store RGB values with a limited range of precision; the constraints of precision, coupled with the limitations of human color perception, make the cone visualization more practical in most cases.

[edit] HSV and color perception

An image, along with its H, S and V components. Note that the H element is the only one displaying colour. Compare the dark on the left side of the barn roof and the white of the snow; in both cases these have colour, but the saturation is very low, causing them to be near-greyscale; the intensity of the barn, however, is much lower than the snow. The green of the grass is highly saturated and of moderate intensity; the blue of the mountains is consistent in colour but varies in intensity and saturation; and the sky has constant colour and intensity but varying saturation.

Artists sometimes prefer to use the HSV color model over alternative models such as RGB or CMYK, because of its similarities to the way humans tend to perceive color. RGB and CMYK are additive and subtractive models, respectively, defining color in terms of the combination of primaries, whereas HSV encapsulates information about a color in terms that are more familiar to humans: What color is it? How vibrant is it? How light or dark is it? The HLS color space is similar and arguably even better than HSV in this respect.

The HSV tristimulus space does not technically support a one-to-one mapping to physical power spectra as measured in radiometry. Thus it is not generally advisable to try to make direct comparisons between HSV coordinates and physical light properties such as wavelength or amplitude. However, if physical intuitions are indispensable, it is possible to translate HSV coordinates into pseudo-physical properties using the psychophysical terminology of colorimetry as follows:

• Hue specifies the dominant wavelength of the color, except in the range between red and indigo (somewhere between 240 and 360 degrees) where the Hue denotes a position along the line of pure purples
• If the hue perception were recreated, actually using a monochromatic, pure spectral color at the dominant wavelength, the desaturation would be roughly analogous to an applied frequency spread around the dominant wavelength or alternatively the amount of equal-power (i.e. white) light added to the pure spectral color.
• The value is roughly analogous to the total power of the spectrum, or the maximum amplitude of the light waveform. However, it should be obvious from the equations below that value is actually closer to the power of the greatest spectral component (the statistical mode, not the cumulative power across the distribution.)

[edit] Transformation between HSV and RGB

An illustration of the relationship between HSV and RGB color spaces.

From RGB to HSV:

Let MAX equal the maximum of the (R, G, B) values, and MIN equal the minimum of those values.

From HSV to RGB:

Hi =
f =
p =
q =
t =

	R = V,	G = t,	B = p
	R = q,	G = V,	B = p
	R = p,	G = V,	B = t
	R = p,	G = q,	B = V
	R = t,	G = p,	B = V
	R = V,	G = p,	B = q

In computer graphics, it is typical to represent each channel as an integer from 0 to 255 instead of a real number from 0 to 1. It is worth noting that when encoded in this way, every possible HSV color has an RGB equivalent. However, the inverse is not true. Certain RGB colors have no integer HSV representation. In fact, only 1/256th of the RGB colors are 'available' in HSV, effectively eliminating a single channel of control from the graphics artist.

[edit] References

• Rafael Gonzalez, Richard E. Woods (2002) Digital Image Processing, 2 ed, Prentice Hall Press. p. 295, ISBN 0-201-18075-8

[edit] See also

• Colorimetry
• Dominant wavelength
• Saturation
• Color space:
  • RGB color model commonly used for color monitors
  • CMYK color model for color printing
  • HSL color space
  • RYB color model the traditional color model used by artists.
  • YUV for PAL television
  • YDbDr for SECAM television
  • YIQ for NTSC television