Wikipedia:WikiProject Color/Normalized Color Coordinates
|Sample color Information Box|
|sRGBB (r, g, b)||(255, 165, 0)|
|CMYKH (c, m, y, k)||(0, 35, 100, 0)|
|HSV (h, s, v)||(39°, 100%, 100%)|
|CIELChuv (L, C, h)||(75, 105, 45°)|
|B: Normalized to [0–255] (byte)|
H: Normalized to [0–100] (hundred)
Color coordinate ranges are a matter of choice and there is no universal standard range for many color spaces (though some ranges may be prevalent). A box having all of the different possible coordinate ranges would be impractical.
Therefore, Wikipedia has chosen standard ranges for the coordinate systems, so as to have consistent coordinates in all color articles. This article describes the chosen systems and provides instructions for conversion to other ranges which might be needed by particular color environments.
Decimal sRGB coordinatesEdit
Every manufacturer has its own color definitions, so this is an internationally acceptable practice. The RGB coordinates describe the amounts of red, green, and blue light which are added together in order to create a particular color. In Wikipedia, the coordinates are presented as three numbers separated by commas, as in this example for the color orange:
- (255, 165, 0)
The coordinates within the parenthesis provide, in order, the relative values of red, green, and blue light. The number in each position ranges from 0 (no color added) to 255 (100% color added). This range was chosen because it is the most commonly used in computer color selection dialogs. (The numbers 0 through 255 fit naturally within one byte and are therefore used to directly drive graphics cards.)
Most image editing programs accept this range. Therefore, RGB should be entered into image editing programs wherever possible because it rarely (if ever) requires conversion.
It is assumed that the exact meaning of the primary colors ("red" for example) is that of the sRGB standard, and that the sRGB gamma function is in use. This color space is not linear. Middle-grey RGB values are near 195,195,195, assuming the γ (gamma) value is 2.6, where , instead of .
Out-of-range values are generally not used. If they are encountered, an scRGB interpretation scaled to 0-255 is recommended.
This is a compact representation of sRGB, using hexadecimal numbering. The hex triplet is based upon the standard format for representing colors within HTML, which is used to construct webpages. This coordinate system should not require any conversion; it should be able to be used directly in HTML source as, for example, in this style attribute:
The CMYK coordinates describe the amounts of each of cyan, magenta, yellow and key (black) pigments (such as inks) which are mixed subtractively in order to create a particular color. In Wikipedia, the coordinates are presented as four numbers separated by commas, as in this example for the color orange:
- (0, 35, 100, 0)
The coordinates within the parenthesis provide, from left-to-right, the relative values of cyan, magenta, yellow, and key. The number in each position ranges from 0 (no pigment used) to 100 (maximum = 100% pigment coverage).
However, the ranges shown for Wikipedia do not correspond to the range normally used as the mathematic basis for computing CMYK, and may not correspond to those accepted by any given color selection dialog. (Probably few, if any, color selection dialogs provide direct access to this coordinate group.)
CMYK is generally something of a disaster[attribution needed], except as used in the internals of a printer driver. Unlike RGB, which is well-standardized as sRGB and which generally has a 1:1 mapping between coordinates and colors, CMYK is device-specific. Even if we assume that two devices will use the same value range and gamma function, we have the problem of radically different notions of what the primary colors actually look like. Not every "cyan" looks exactly the same. Multiple CMYK values will map to the same perceived color. One may minimize the use of black to save ink costs and avoid soggy paper, or maximize the use of black to reduce speckles. Printing oddities, such as dot gain and paper variations, serve to make the situation quite hopeless[attribution needed].
|Coordinate Group||Usage||Converting from Wikipedia coordinates|
|0–1.0, 0–1.0, 0–1.0, 0–1.0||
||Divide each of the Wikipedia coordinates by 100.|
|0–100, 0–100, 0–100, 0–100||
The HSV color space coordinates describe a color in terms of the hue, given as degrees, combined with a saturation and a value, both represented as percentages. (Value is similar to brightness in this usage.) In Wikipedia, the HSV coordinates are represented as three numbers separated by commas and identified as either degrees or percentage, as in this example for the color orange:
- (39°, 100%, 100%)
The coordinates within the parentheses provide, from left-to-right, the relative values of hue, saturation, and value.
The first number, the hue, ranges from 0° to 359°. This defines the overall hue of the color. The following table shows the correspondence between major colors and the angle:
Angles falling between these major color points yield colors intermediate to the bracketing angles; the color Amber, for example, falls at 45°, between orange and yellow. For angles increasing above 300° (magenta), colors become progressively redder as if red resided at 360°.
The second number, the saturation (color intensity), ranges from 0% to 100%, with 100% indicating a very intense color and 0% indicating grey (that is, being completely neutral or without hue).
The third number, the value (or brightness), ranges from 0 to 100%, with 0% indicating black and 100% indicating the brightest possible intensity of a color, whether white or otherwise, as limited by a maximum in RGB color space. In HSL color space, on the other hand, only white can have a lightness of 100%.
This coordinate system is problematic, because programs that accept this system use several different ranges of numbers on input. Some of these are listed in the table below.
|Coordinate Group||Usage||Converting from Wikipedia coordinates|
|0°–360°, 0–1.0, 0–1.0||
||Strictly speaking, this conforms to the Wikipedia range, since 100% = 1.0. Divide saturation and value coordinates each by 100.|
|0°–360°, 0%–100%, 0%–100%||
|0–255, 0–255, 0–255||
||Multiply hue by 0.71; multiply saturation and value each by 2.55|
|0–1.0, 0–1.0, 0–1.0||
||Divide hue by 360; divide saturation and value each by 100|
Most image editing programs probably accept the RGB value, which should also be more easily used.
CIELChuv is a perceptually uniform color space consisting of lightness, chroma and hue coordinates. It is derived from the CIELUV space, usually based on the 2° observer and the standard Illuminant D65 representing daylight.
huv is an angle that is normally given in degrees. L* is in the range 0% to +100%. u* and v* are typically in the range −100% to +100% but may exceed it. C*uv is the hypotenuse of u* and v*, so it typically ranges from 0% to 100% × √ ≈ 141%, but may extend beyond, for example, 179% for
Microsoft HSL inputsEdit
Many Microsoft Windows programs (such as Microsoft Paint) provide inputs to accept HSL (hue, saturation, lightness) color coordinates in the range 0–240, 0–240, 0–240. These can be approximated by multiplying the hue of the HSV coordinates by 0.67 and multiplying the saturation and value each by 2.4; then using the value coordinate as input to the luminance coordinate. However, HSL does not exactly correspond to HSV, so the result may be not be an accurate color rendition. (Proper conversion from HSV to HSL is complex.)
However, most (if not all) of these programs also accept RGB, which can typically be entered without conversion. Therefore, it is usually best in these programs to use the RGB coordinate.