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Interactive 1931 CIE Chromaticity Diagram

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This interactive CIE 1931 Diagram requires Silverlight which is most likely already installed on your computer.

Wikipedia has a good article on CIE 1931 color space.

Moving the cursor in the diagram will show the CIE diagram coordinates (x, y, z) and its corresponding (R, G, B) values in the upper-left panel.

Clicking the left mouse button places an arrow pointing to the clicked point, and the upper-left CIE coordinates panel freezes the values. Clicking the left mouse button again removes the arrow, and the CIE coordinates values will follow the cursor again.

Lower-left panel displays monochromatic light information. The monochromatic light wavelength can be changed by using the wavelength slider.  

If "Show monochromatic mark" is checked, a dot corresponding to the selected monochromatic light wavelength will be displayed along the boundary of the diagram.

If "No added white" is checked, only the triangle region which color can be truly rendered by a standard monitor is displayed. Any point of the CIE diagram outside this region has at least one of the (R, G, B) being negative. When "No added white" is not checked, the color of each of these points is rendered by adding white color (i.e. increaseing R, G and B in the same amount) until no more negative values among (R, G, B). 

CIE chromaticity diagram is a 2-D diagram in a 3-D (xyz) space, so the best way to present it is to draw it in the 3-D xyz space and allow it to be looked at from different angle. Biyee has a limited version of 3D CIE 1931 Diagram (Java 3D needs to be installed).   

Since it is impossible for a color monitor with RGB phosphors to display the full spectrum of colors of a true CIE diagram, the part that has negative R, G, or B values are displayed by adding white to them until the most negative value is raised to zero.

The following table lists different variants CIE 1931 chromaticity diagram

Just diagram Three simple 2-D CIE 1931 diagrams
Diagram w/o added white Three diagrams with negative R, G, B values replaced with zero by adding white to the entire diagram.
Honest Diagrams Three diagrams that do not show the part that cannot be reproduced with RGB

These diagrams are based on 1931 2-degree CIE xyz color matching functions that remain international standards in both colorimetry and photometry.  International Telecommunication Union uses 1931 CIE color matching functions in their recommendations for worldwide unified colorimetry (ITU-RBT.709-4, ITU-R  BT.1361).  Most color monitors comply with the standard.  This makes it possible to display 1931 CIE diagrams correctly on different color monitors.  

There are other color coordinate systems most of which are not any kind of  transform of 1931 CIE system, so it is impossible to display diagrams of those system correctly on different monitors that are calibrated with 1931 CIE system.