Method and system for displaying colors utilizing tristimulus values

A system for displaying color comprising:

• display means for generating and displaying an image including a reference light image in a first display area of said display means and a color image in another display area of said display means in response to applied electrical signals;
• information input means connected to said display means for receiving, as an input, information representative of a desired color to be displayed and for converting said input information into said applied electrical signals to cause said display means to generate and display in the other display area a color representative of said input information;
• analyzing means optically coupled to said display means for analyzing the reference light image and providing analyzed values representative thereof;
• standard means independent of said analyzing means for continuously producing standard values which represent a predetermined standard light;
• comparator means for continuously comparing said analyzed values and said standard values and for producing error signals representative of the difference between said analyzed values and said standard values, said error signals being provided to said display means for modifying said applied electrical signals in accordance with the difference between the reference light image values and said predetermined standard image value.

A color display system comprising:

• a data input device for keying a set of numerical data;
• first means for generating a set of first electrical signals representing the tristimulus values of a desired color in response to said keyed numerical data;
• and
• second means for generating radiations of different basic colors in response to said electrical signals;
• said first means comprising a plurality of comparators 14, 15, 16 each having a first input terminal receptive of a respective one of said first electrical signals and a second input terminal receptive of an error correction signal to generate a set of second electrical signals X.sub.c ', Y.sub.c ', Z.sub.c ',
• said second means comprising a cathode ray tube 18 having a plurality of electron beam generating means and a plurality of light emissive areas for generating radiations of different wavelengths in response to impingement of the electron beams thereo, means 12 for converting said second electrical signals in accordance with the emission characteristics of said light emissive areas to modulate the intensity of said electron beams, means for causing said electron beams to produce a white light in a specified area 21 of said cathode ray tube screen, means for deflecting the intensity modulated electron beams to produce an image which is a blend of said radiations of different wavelengths in different areas of said cathode ray tube screen, a spectral component analyzer 23 for analyzing the spectral components of said white light for generating a set of third electrical signals Xw', Yw', Zw' representing the tristimulus values of said white light, a plurality of second comparators each having a first input terminal receptive of a respective one of said third electrical signals Xw', Yw', Zw' and a second input terminal receptive of a respective one of a set of reference signals Xw, Yw, Zw representing the tristimulus values of a reference white light to generate a set of fourth electrical signals .DELTA.Xw, .DELTA.Yw, .DELTA.Zw representing the difference between said third and reference signals, and means for multiplying said fourth electrical signals by the inverse matrix of a set of said input data to generate a set of fifth electrical signals .DELTA..alpha..sub.1w, .DELTA..alpha..sub.2w, .DELTA..alpha..sub.3w for application to the second input terminals of said first comparators.

A method of color control in a visual display using a cathode ray tube which has a separate electron source for each of three primary colors comprising:

• (a) inputting values for Hue, Value and Chroma according to the Munsell color system into a computer from a data input device;
• (b) determining the tristimulus values for each of the three primary colors in said computer corresponding to the Munsell color system values inputted to the computer;
• (c) using the determined tristimulus values to produce signals and energizing said electronic sources with said signals;
• (d) focusing at a given position on the screen of said cathode ray tube, the beams produced by each of said electron source to produce a white spot;
• (e) analyzing said white spot and producing tristimulus values for each of said three primary colors:
• (f) generating tristimulus values for each of said three primary colors which values represent absolute white, said step of generating being independent of step (e);
• (g) continuously comparing in said computer each of the tristimulus values obtained in step (e) with said values obtained in step (f) which represent absolute white;
• (h) producing error signals for each of the three primary colors determined from the comparison of step (e);
• (i) modifying the values determined by said computer in step (b) using said error signals;
• (j) repeating step (c) using the modified values obtained in step (i) in place of the original values used in step (c);
• and
• (k) repeating steps (d) to (j).