![]() ![]() That’s why we can capture colors in cameras and view them with colors close enough on a computer screen: different SPDs may have the same color coordinates. Since a 3D coordinate system for color does not carry information about actual SPD of the source, two light sources with different SPD may have the same coordinates, their SPD weighted against standard observer gives the same numbers. It takes a reference CIE XYZ white for its definition so L*=100, a*=b*=0 are the coordinates of reference white. It has 3 coordinates (3D color space), L* for luminance, a* for a green-magenta axis and b* for blue-yellow axis. There are other common 2D projections of other 3D color coordinate systems like CIE u’v’.Īnother color coordinate system derived from CIE XYZ is CIE L*a*b*. The concept of this CIE xy 2D plot (or other 2D plot of a 3D color space) is important for the next articles. ![]() CIE xy coordinates (without capital Y) represent a 2D plot of CIE 1931 XYZ color space, like a city map… and like in a 2D city map some information is discarded, but we get a picture of locations quickly. Since a Y coordinate (capital Y) is kept in CIE xyY (it’s a 3D coordinate system after-all), original XYZ values can be restored. In that CIE xyY color space, XYZ values (3D coordinates) are normalized to lowercase x,y,z values with the condition x+y+z=1, a scale conversion. A similar approach is CIE xyY color space, derived from CIE XYZ. A city may be a 3D space, but we find it useful to represent a city in a 2D plane, like a paper map with north-south, west-east locations. Like our world, a city is a 3D space: north-south, west-east, but also an up-down location of a building. Wikipedia has a very good definition of CIE XYZ and where X, Y & Z coordinate values come from. Measuring color in CIE 1931 XYZ coordinates (the most used color coordinate system for measuring) is about weighting the spectral power distribution (SPD, distribution of how much light is coming to measurement device for each visible wavelength) against a “model” of human vision called CIE 1931 2º standard observer (or just “standard observer” to keep it short). There are several coordinate choices that map to color spaces like CIE 1931 XYZ (or just CIE XYZ onwards), which is a 3D coordinate system for visible colors with X, Y and Z coordinates. Such number transformations are possible, because colors (visible colors seen by humans) can be defined objectively as coordinates in a color space that covers human vision, like the CIE 1931 color space. This is where color management comes into play: if applications know the actual gamut of that monitor, they can translate this “0,255,0” sRGB value to another set of RGB values that represent the same color (or fairly close) in a bigger color space: ![]() But if you do the same thing in a wide-gamut monitor configured to show its full gamut, that “0,255,0” RGB value will show native gamut green 255 and it will look over-saturated. With a common monitor (sRGB monitor) you can output its contents to the monitor directly, without conversions or color management, and you will see the green color that is “fairly close” to color information stored in that JPEG file. For example, you have an sRGB 300×300 JPEG image that is just a green background (RGB values “0,255,0” in sRGB). The first thing photographers need to know is that their wide-gamut monitors are meant to be used in color-managed applications: applications that work in a color managed environment. 2) Color Management and Color Coordinates That’s the main reason that leads professionals and photo hobbyists into seeking monitors with a wider gamut which covers a large percentage of color spaces like AdobeRGB 1998 or eciRGBv2. This color space is not able to cover colors printable with current technology like offset printing or a domestic inkjet printer – there are colors like cyan-turquoise green that are printable with such devices, but cannot be shown on an sRGB monitor. For historical reasons, sRGB and other similar color spaces like Rec.709 cover the same gamut (subset of visible colors) as CRT monitors. The Internet and most computer content is meant for this particular color space. Common monitors try to cover a minimum standard color space known as “ sRGB” with their red, green and blue emitted light. As you might already know, monitors, TVs, mobile devices, etc., can show us colors using a mixture or Red, Green and Blue (RGB) light. ![]()
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