Method and device for the true-to-original representation of colors on screens

Abstract

Described is a method and a device for screen calibration for the true-to-original reproduction of surface colors, the spectral reflection distribution of which is known, wherein by setting parameters the screen can be influenced using software and an electronic controller in each partial region of the screen. The disclosure is characterized in that an observer adapts the reproduced color impression of the screen to the color impression of an original in each partial region of the screen, wherein the original is compared to the screen colors immediately thereafter on the screen surface and the screen parameters are varied until the color impressions of the original and of the screen appear identical to the observer on the respectively viewed partial screen, viewed from a predefined observer angle, and the settings performed are stored in a screen profile.

Claims

1. A method for the screen calibration for the true-to-original reproduction of surface colors, the spectral reflection distribution of which is known, on a screen, which is operated under incident light from at least one light source with angle of incident outside a gloss angle and with known spectral light distribution, whereby the screen is influenced by adjustment of parameters with software and electronic control in each of a plurality of partial areas of the screen, the method comprising: adjusting a reproduced color impression of the screen in each of the plurality of partial areas of the screen to an original color, whereby the original color is compared to screen colors directly bordering the screen surface, and whereby the screen parameters are varied until the color impression of the original color and the screen appear identical when viewed from a predefined observer angle; storing settings of the screen parameters in a screen profile; positioning at least one mask in front of the screen, wherein the at least one mask has at least one window distributed across the screen, whereby the at least one window is partially covered by an original color of a test surface color, and wherein behind each uncovered area of the window on the screen, a color reproduction allocated to the test surface color is created; controlling the screen with software operated on a computer to change and adjust the brightness of the reproduced color, until a brightness difference between the original color and reproduced color under illumination of the screen is reduced, wherein brightness values are stored as support points and therefrom a brightness profile created which controls an absolute brightness for each color reproduced in a pixel of the screen; and automatically executing brightness calibration and determination of support points for the brightness profile of the screen, wherein as a camera is viewing the mask, for each window of the mask, an area of the surface colors and the colors reproduced by the screen are selected and measured within the area and average color signals are produced, wherein the color signals are supplied to the computer which controls the screen, and wherein the brightness of the color signals are changed repeatedly until, in each window, color signals created via the test surface color and the color reproduction are of identical magnitude.

2. The method according to claim 1, wherein the parameters are varied until the color impression of the original and the screen appear identical when viewed from the predefined observer angle by a standard observer in accordance with CIE 1964-10 degree or CIE 9131-2 degree.

3. The method according to claim 1, wherein the camera is equipped with an optical filter, which together with a spectral sensitivity of the camera, results in a total spectral profile of the picture taken, which corresponds to a spectral brightness (V2) of a standard observer.

4. The method according to claim 1, wherein color stimuli as a result of a reflection of the light at the screen surface in a direction of a location is measured in their spectral distribution and their intensity, wherein the color stimuli are described for a standard observer as reflected color values of the screen and differences of color values of the original colors and the reflected color value are reproduced on the screen.

5. The method according to claim 1, wherein color stimuli resulting from reflection of the light at the screen surface in a direction of a position is measured during measurement of the screen profile during turned on lighting and then are contained in an optionally stored screen profile.

6. The method according to claim 1, wherein the screen is positioned in a box, a horizontal screen center is illuminated in the screen center in a vertical section under 45 degrees, wherein the illumination is executed through extended rod-shaped light sources that are mounted above and/or below the screen, and a homogenization of the lighting distribution on the screen is achieved whereby the masks are mounted in a ray path of the light from the light sources to the screen, which as a result of their configuration, block or let pass fractions of the light rays from the light sources on the way to the screen depending on location and/or angle.

7. The method according to claim 1, wherein illumination in a room environment is generated from the ceiling and the light sources are positioned so that light strikes the screen under a 45 degree angle.

8. The method according to claim 1, wherein spectral distribution of the lighting is measured by a spectrometer mounted directly on the screen and results of the spectral light distribution are taken into account when preparing the screen profile.

9. The method according to claim 1, wherein the screen is operated under an internal light source in a box and additionally external light falling on an observation surface with the same or other spectral distribution is included in calculating the reproduction of the color, and at the same time, the color distribution separated from light coming from the outside and light from the internal light source is ascertained and the color reproduction is represented as total of color values resulting from the internal and external illumination.

10. The method according to claim 9, wherein brightness distribution of the light impinging from the outside is measured during turned-off light source via sensors that are distributed through the box.

11. The method according to claim 1, further comprising using variable basic color-matching curves for calculating colors from the spectral reflection properties of original colors and for calculating color reproduction via the screen in an order of magnitude of a color and an observation angle derived therefrom, and wherein a color display in areas of almost the same colors are segmented and an allocated observer angle for a segment is determined from as a size proportion of given color represented in a picture.

12. The method according to claim 1, wherein for the color reproduction with different standard observers, a data bank is built in which basic color-matching curves of various observers are stored, further comprising using the basic color-matching curves as a function of an observer angle, wherein color values of original colors are created from their spectral reflection from the variable basic color-matching curves, wherein colors displayed on the screen resulting from their spectral distribution are described and color values are calculated for building screen profiles dependent on different observer angles, wherein the screen profiles are stored in real time processing for color reproduction of pictures or as precalculated profiles in a data bank and retrieved subject to a selected observer angle.

Description

LIST OF FIGURES

(1) FIG. 1a: Lighting box with adjacent screen for color equalization between mode in the lighting box and reproduction on the screen (State of the Art);

(2) FIG. 1b: Lighting box in FIG. 1a in cross section and longitudinal section (State of the Art);

(3) FIG. 2: Lighting box with two frames, one for the mode and one for the reproduction, in cross section and longitudinal section (State of the Art);

(4) FIG. 3: Lighting box of the invention with screen;

(5) FIG. 4a: Detailed view of an observation mask with original and reproduced color in top view and cross section;

(6) FIG. 4b: Screen with observation mask with a multitude of windows distributed across the screen in the observation mask;

(7) FIG. 5a: Schematic representation of the lighting situation of a screen with two fluorescent tubes;

(8) FIG. 5b: Model light masks in longitudinal section;

(9) FIG. 5c: Light mask from FIG. 5b in longitudinal section rotated by 90 around longitudinal;

(10) FIG. 6: Lightning box of the invention with screen and light sensor On the screen edge;

(11) FIG. 7: Schematic representation of the true-to-original color reproduction on a screen with variable color-matching curves;

(12) FIG. 8: Schematic representation of the method create a screen profile.

LITERATURE

(13) [1] Mark. D. Fairchild, Color Appearance Models, Addison-Wesley Longman, Inc, Reading Mass., 1998, ISBN 0201-63464-3. [2] CIE publication 159-2004: A Colour Appearance Model for Colour Management systems: CIECAM02 [3] G. Wyszecki, W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae, 2nd. Edition, John Wiley & Sons, New York 1982, Chapt. 5.6 [4] F. Vienot, Report on a fundamental chromaticity with physiologically significant axes, Proc. 9th Congress of the International Colour Association, SPIE Vol 4421 (2202), p. 565-570

LIST OF USED REFERENCE SIGNS AND VARIABLES

(14) 1 Observation box 2 Monitor or Screen 2.1 Observation area 2.2 Surface of a screen 3 Illumination or Light 3.1 Direct Incidence of Light 3.2 Indirect Incidence of Light 3.3 Indirect Incidence of Light 3.4.1 Light Mask 3.4.2 Light Fraction 3.5.1 Light Mask 3.5.2 Light Fraction 4 Observation Surface 4.1 Color sensor/Original 4.1.1 Test Color or reflected rays 4.2 Color Reproduction 4.2.1 Light of Reproduction 4.3 Frame 5 Observer 6 Mask 6.2 Window 7.1 Light intensity of Lamp LI on the Screen 7.2 Light intensity of Lamp L2 on the Screen 7.3 Light intensity of L1 and L2 on the Screen 8 Light Sensor 9 Position for spectral measurement of external light 10 Data bank 10.1 User-specific color-matching curves 10.2 User-specific screen profile 11.1 Color areas of original 11.2 Color areas of reproduction 12 Backward Model 13 Radiometric measurement 14 Color-Value Calculation 15 Color Values 16 Signal Value Calculation A Distance D Diameter i Observation Index I Light intensity K Standardizing Constant L1-L3 Lamp P Scatter Lamp Pi/Pi() Screen profile for observer angle R1, R2, R3 Reflectors Rp,Gp,B.sub.p Control Signals R, G, B Input signal S Spectral Distribution S,.sub.B Spectra of the Screen Color V Brightness Sensitivity x (),y(),z() Color-Matching Curve xi (,), yi (,),zi (,) Color-Matching Curve X,Y,Z Standard Color Values Xw,Yw,Zw Color Values for a reference white Xp, Yp, Zp Color Values to be reproduced Xr,Yr,Zr Color Values of reflected Fractions Xp.sub.(F, Yp,.sub.F, Zp,.sub.F Color Values from External Light Illumination Xp(),Y.sub.P(),Zp() Color Values for Observer Angle a Observer Angle to Light Incidence () Spectral Reflection Observer Angle/Opening Angle of a Color Surface