Visual calibration target set method

Abstract

A novel process of visual calibration of a computer display or the like in volves adjusting the appearance and relative appearance of targets and su targets displayed on the display. An objective method is provided for determining the precisely optimal brightness setting for CRT displays, which method is also applicable to the setting of the “Black Level” control on some FPDs. A precise method is provided to visually determine conformity of a display's tonality to a given standard tone curve, for example a gamma 1.8 curve, which is embodied in one of the preferred calibration target sets. The need to sense and therefore be able to control and to verify the correct gray balance of the entire tone scale of the display is met. The problem of verifying the similarity of the tone curve in the display profile and that of the actual calibration is solved. By converting a preferred RGB gamma target into CIE Lab image data through an ideal display profile of the correct gamma, a new kind of target is taught.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Application No. 60 / 185,969, filed Mar. 1, 2000.FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not applicable.CD-R APPENDIX[0003]This application includes a one-disk CD-R Appendix, the full contents of which are incorporated by reference herein. The disk contains the following files, listed by file name, creation date and file size in bytes: “ColorBlind Video Startup” created Jun. 22, 1999, 100K; “ColorBlind_Video_Startup.exe” created Sep. 16, 1999, 160K; “Complete_Text.txt” created Feb. 22, 2001, 40K; “Contents_of_CD.txt” created Feb. 22, 2001, 4K; “Lab Color Space Profile” created Aug. 4, 1997, 7K; “Prove it!” created Aug. 27, 1999, 4,116K; “Prove it! Installer” created Jul. 20, 1999, 2,251K; “Prove it_Beta.exe” created Jul. 16, 1999, 11,555K; and “Prove_it_Setup.exe” created Nov. 18, 1999, 7,432K.FIELD OF THE INVENTION[0004]This invention relates to the calibration of computer mo...

AI Technical Summary

Benefits of technology

[0034]Second, the current invention provides a precise method to visually determine conformity of a display's tonality to a given standard tone curve, for example a gamma 1.8 curve, which is embodied in one of the preferred calibration target sets of the invention. The current invention clearly reveals conformity with the standard tone curve for each relevant sub-region of the tone scale, thus assuring a visual tone match between the displayed image and the image data when simulations are performed (see FIGS. 13-17). The prior art methods provide only limited ability to verify the actual tonality of a display and its conformity to a standard tone curve, because the methods of the prior art do not reveal the tonality of each relevant subsection of the tone curve. Also, some prior art methods rely on a gridded or halftone pattern of mixed dark and light tones instead of a pattern of alternating horizontal lines, rendering them essentially useless for reliable tone calibration of CRT displays because of limitations of the electronics of CRT displays. The present invention relies primarily on patterns of mixed light and dark tones, which consist of horizontal lines containing only one value, for gamma or tonality assessment. The invention relies primarily on such lined patterns, which complement the nature of currently ubiquitous display hardware used for imaging. The invention also makes it feasible to implement a solution which, in the visual calibration targets, includes the mixing of pixels of different values in individual, horizontal rows of pixels, especially in the Gray Balance Method Two procedure and target. Flat panel displays, which are not in widespread use for imaging, are likely to be much better suited to use with such mixed pixel values in individual horizontal rows of pixels in the visual calibration targets than are CRT displays of the present day. The invention also makes it possible to combine the gamma and gray balance adjustment functions into a single target set which relies on a combination of patterns such as described below in the Gray Balance Method Two targets (see FIGS. 9 and 23).

[0036]The second preferred embodiment of the gray balance capability of the invention (see FIGS. 23, 24 and 25, illustrating what is referred to herein as Gray Balance Method Two, Increased Precision) extends the ability to see even further into the shadows by utilizing a pattern of dots, at the risk of making this embodiment function less ideally with CRT displays, in terms of correct lightness in the blended areas. This embodiment allows double the gray balance matching precision in the three-quartertones, relative to the first embodiment, and brings precise-matching to an even darker value of RGB (40, 40, 40) in this target example designed for use at gamma 2.2. This is more than 5 / 6ths of the way from white to black in the input value scale, and is a tone which, in this case of a gamma 2.2 version of the target, equals only 2% of the absolute luminosity of the white. This second preferred embodiment also increases the precision of the quartertone matching when used with displays having color crossovers in the lighter half of the tone scale. Flat panel displays are more prone to this problem than are CRT displays. Numerous variations on this part of the invention are possible, as necessitated by the nature of the display, the nature of the software interface, or the need for simplicity in the method. For example, more sub-targets can be added at almost any lightness where user control is needed to force correct tonality or gray balance. Also, a single target set of a type broadly similar to the Gray Balance Method Two, Increased Precision target (see FIGS. 23, 24 and 25) can be used for both gamma and gray balance adjustment. By combining tones in new and more complex patterns than the prior art, the invention makes it possible to extend gray balance from the white to a midtone value, and from there to other values, and so on, until all important parts of the tone scale have been reached with the ability to match them to the color of the white.

Problems solved by technology

The prior art methods provide only limited ability to verify the actual tonality of a display and its conformity to a standard tone curve, because the methods of the prior art do not reveal the tonality of each relevant subsection of the tone curve.

Also, some prior art methods rely on a gridded or halftone pattern of mixed dark and light tones instead of a pattern of alternating horizontal lines, rendering them essentially useless for reliable tone calibration of CRT displays because of limitations of the electronics of CRT displays.

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