Color calibration of color image rendering devices

• US 20060280360A1
• Filed: 08/31/2005
• Published: 12/14/2006
• Est. Priority Date: 02/26/1996
• Status: Active Grant

• Current Assignee: RAH Color Technologies LLC
• Original Assignee: RAH Color Technologies LLC
• Inventors: Holub, Richard A.
• Granted Patent: US 7,728,845 B2
• Time in Patent Office: Days
• US Class Current: 382/162
• CPC Class Codes: G01J 2003/2866 Markers; Calibrating of scan
• CPC Class Codes: G01J 2003/466 Coded colour; Recognition of predetermined colour; Determining proximity to predetermined colour
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0202 Mechanical elements; Supports for optical elements
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/0262 Constructional arrangements for removing stray light
• CPC Class Codes: G01J 3/0264 Electrical interface; User interface
• CPC Class Codes: G01J 3/0272 Handheld
• CPC Class Codes: G01J 3/0289 Field-of-view determination; Aiming or pointing of a spectrometer; Adjusting alignment; Encoding angular position; Size of measurement area; Position tracking
• CPC Class Codes: G01J 3/0291 Housings; Spectrometer accessories; Spatial arrangement of elements, e.g. folded path arrangements
• CPC Class Codes: G01J 3/18 using diffraction elements, e.g. grating gratings per se G02B
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: G01J 3/463 Colour matching
• CPC Class Codes: G01J 3/50 using electric radiation detectors
• CPC Class Codes: G01J 3/506 measuring the colour produced by screens, monitors, displays or CRTs
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G03B 27/547 colour mixing heads
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20072 Graph-based image processing
• CPC Class Codes: G06T 7/80 : Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• CPC Class Codes: G06T 7/90 : Determination of colour characteristics
• CPC Class Codes: G09G 2320/0285 : using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/0626 : for control of overall brightness
• CPC Class Codes: G09G 2320/0666 : for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/0693 : Calibration of display systems
• CPC Class Codes: G09G 2330/021 : Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 : the light being ambient light
• CPC Class Codes: G09G 2360/147 : the originated light output being determined for each pixel
• CPC Class Codes: G09G 3/3413 : Details of control of colour illumination sources
• CPC Class Codes: G09G 5/02 : characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607
• CPC Class Codes: H04N 1/6033 : using test pattern analysis H04N1/6055 takes precedence
• CPC Class Codes: H04N 1/6052 : Matching two or more picture signal generators or two or more picture reproducers
• CPC Class Codes: H04N 17/02 : for colour television signals
• CPC Class Codes: H04N 17/045 : Self-contained testing apparatus
• CPC Class Codes: H04N 23/13 : with multiple sensors
• CPC Class Codes: H04N 23/88 : for colour balance, e.g. white-balance circuits or colour temperature control
• CPC Class Codes: H04N 9/12 : Picture reproducers H04N9/11 takes precedence
• CPC Class Codes: H04N 9/3182 : Colour adjustment, e.g. white balance, shading or gamut white balance per se H04N9/73; control of amplitude of colour signals H04N9/68; colour control circuits for displays in general G09G5/02, G09G3/2003, G09G3/3607
• CPC Class Codes: H04N 9/3194 : including sensor feedback
• CPC Class Codes: H04N 9/68 : for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86
• CPC Class Codes: H04N 9/73 : Colour balance circuits, e.g. white balance circuits or colour temperature control camera processing pipelines for colour balance H04N23/88

Abstract

Color calibration of color image rendering devices, such as large color displays, which operate by either projection or emission of images, utilize internal color measurement instrument or external color measurement modules locatable on a wall or speaker. A dual use camera is provided for a portable or laptop computer, or a cellular phone, handset, personal digital assistant or other handheld device with a digital camera, in which one of the camera or a display is movable with respect to the other to enable the camera in a first mode to capture images of the display for enabling calibration of the display, and in a second mode for capturing image other than of the display. The displays may represent rendering devices for enabling virtual proofing in a network, or may be part of stand-alone systems and apparatuses for color calibration. Improved calibration is also provided for sensing and correcting for non-uniformities of rendering devices, such as color displays, printer, presses, or other color image rendering device.

Claims

1. An instrument for calibrating a projection color video display having a housing and a microprocessor-based system for producing images and optics for projecting said images onto a surface, said instrument comprising:

one or more sensor elements in said housing which receive light that is reflected from said surface for providing color measurement data representative of one or more known color images when projected on said surface for calibration of said projection display; and

said microprocessor-based system calibrates color of said projected images in accordance with said color measurement data and said known color images.

2. The instrument according to claim 1 wherein said light received by said sensor elements is received via said optics, and directed by an optical element to said sensor elements.

3. The instrument according to claim 1 wherein said optics represents first optics and said instrument further comprises second optics through which said sensor elements receive light reflected from said surface.

4. The instrument according to claim 1 wherein said microprocessor-based system enables calibration by conversion of said color measurement data into device-independent units enabling comparison of measured color values of said color measurement data and reference color values from said known color images to produce color error data useable in modifying at least one of linearization curves for one or more color channels of said projection display or a color transformation that embodies color mixture characteristics of said color channels of said projection display.

5. The instrument according to claim 1 wherein said optics represents a lens system comprising at least one lens capable of being positioned near the source of projected light and of forming an image of the screen of said projection display, and said sensor elements receive light through said optics from said surface.

6. The instrument according to claim 1 wherein said sensor elements have at least one of optical filters, fiber optics, or wavelength separating element, through which reflected light is received from said screen.

7. The instrument according to claim 1 wherein said sensor elements are capable of imaging, and said color measurement data further comprise information regarding spatial non-uniformity of color reproduction across said screen of said projection display.

8. A digital theater system for reproducing color images on a screen in a room in accordance with tolerances for consistency of color reproduction at multiple sites comprising:

an image display device providing color images on said screen;

a color measuring instrument for non-contact measuring of said color images on said screen;

a processor for controlling at least said image display device and said color measuring instrument, said processor being capable of rendering one or more calibration images on said screen via said image display device, receiving color measurements from said instrument representative of said rendered calibration images, and modifying color transformations employed by said processor in rendering color images on said screen in accordance with said color measurements;

memory accessible by said processor for storing at least said calibration images, the color images to be rendered by the image display device, and said color transformations; and

a network interface coupled to said processor enabling import or export of at least the color images to be rendered by the image display device from or to at least one other of said multiple sites.

9. The system according to claim 8 wherein said image display device represents one of a digital projector or projection display providing images onto said screen.

10. The system according to claim 8 wherein said image display device represents a self-luminous flat panel having said screen.

11. The system according to claim 8 wherein said room has walls and said color measurement instrument is mounted onto the wall.

12. The system according to claim 8 wherein said color measuring instrument is integral with the image display device.

13. The system according to claim 8 further comprising one or more speakers for outputting audio associated with said color images, and said color measuring instrument is coupled to one of said speakers.

14. A method for detecting color errors in a reproduction on a display surface produced by a rendering device, said reproduction representing a source digital image having pixels in one or more color channels, said method comprising the steps of:

measuring spatial non-uniformities of rendering across said display surface;

capturing a digital image of said reproduction in which said digital image is represented by pixels in different color channels;

generating at least one histogram of the captured digital image of pixels in one or more of said color channels;

modifying said source digital image at least to simulate said spatial non-uniformities of rendering;

cross-correlating one or more regions of said histogram with similar regions of a histogram of pixels of said modified source digital image; and

analyzing said cross-correlated histograms to determine the color error of said reproduction.

15. A portable device for automatic calibration of a color display comprising:

a housing having a display and a camera attached or built into said housing;

a processor for calibrating color of said display in accordance with one or more images of said display captured by said camera;

one of said camera and said display being movable with respect to the other to enable said camera to capture one or more images of said display to enable said calibration; and

one of said camera and said display being movable with respect to the other to capture images other than of said display.

16. The portable device according to claim 15 further comprising an arm having a first end attached to said housing and a second end attached to said camera, in which said camera is pivotally mounted at said second end to enable said camera to be oriented in a first mode to capture one or more images of said display to enable said calibration, and in a second mode to capture images other than of said display.

17. The portable device according to claim 15 wherein said housing has an upper portion with said display and a lower portion with said camera, said upper portion is pivotally mounted with respect to said lower portion to enable said upper portion to be pivoted in a first mode to capture one or more images of said display to enable said calibration, and in a second mode to capture images other than of said display.

18. The portable device according to claim 15 wherein said portable device represents a cellular telephone handset and said camera is coupled by an arm to said housing which is pivotal in one or more dimensions to orient said camera in a first mode to capture one or more images of said display to enable said calibration, or in a second mode to capture image other than of said display.

19. The portable device according to claim 15 wherein said processor calibrates color of said display in accordance with color image data captured by said camera representing color of one or more calibration forms outputted by said processor on said display.

20. The portable device according to claim 15 wherein said camera is capable of capturing images providing information regarding spatial non-uniformity of color reproduction across said screen of said display.

21. The portable device according to claim 15 wherein said camera is capable of being oriented for imaging another color display of an image display device to provide color image data representative of said another color display, and one of said processor or said image display device enables calibration of said another color display in accordance with said color image data.

22. The portable device according to claim 15 wherein said camera is capable of being oriented to capture an image representative of amount of ambient illumination, and said display has a backlight which is turned on or off in accordance with said amount of ambient illumination.

23. A projector for rendering color image data on a display surface comprising:

optics capable of forming an image of said display surface with variable focus;

an array sensor capable of receiving said image of said display surface and producing electrical signals representative of said image, wherein said array sensor is calibrated to compensate for differences in sensitivity of different elements of said array sensor and is capable of responding to different wavelength bands of light;

a controller comprising a microprocessor with memory for stored programs and an interface to a transmitter/receiver module, wherein said stored programs enable compensation for optical distortions of said image and color calibration of said projector according to a device independent standard.

24. The projector according to claim 23 further comprising audio signaling electronics in communication with said controller for producing and receiving audio signals capable of assisting a user to calibrate said projector.

25. The projector according to claim 23 wherein said color calibration further comprises enabling spatially uniform color reproduction on said display surface.

26. The projector according to claim 25 wherein said spatially uniform color reproduction comprises spatially uniform neutral balance.

27. A hand-held device comprising:

a housing having a screen capable of displaying information at a first resolution and at a second resolution in which said first resolution is higher than said second resolution;

optics attachable to said housing for providing magnification of said information at least when displayed in said first resolution.

28. The device according to claim 27 wherein said optics are attachable to said housing by one or more arms, wherein each said arm is pivotal around one or more joints, to enable positioning of said optics with respect to said screen.

29. A user-interface operable on a hand-held device having a camera comprising:

a controller;

an output device operating responsive to said controller, said output device representing one of a display for visually conveying, or a speaker for audibly conveying, a menu of selections; and

said menu of selections comprising at least one of a first selection for adjusting the back light intensity of said display responsive to readings of environmental illumination by said camera, a second selection for using said camera to calibrate color or spatial uniformity of illumination of said display, or a third selection of using said camera to calibrate color or spatial uniformity of illumination of the display of a device other than said hand-held device.

30. A method of calibrating a digital camera comprising the steps of:

retrieving data on first spectral curves characteristic of the response of the color channels of said digital camera;

retrieving data on second spectral curves characteristic of the output of the color channels of a display;

calculating third spectral curves resultant from adding said second spectral curves of the color channels in varying proportions;

calculating first tristimulus values using said third spectral curves and the color matching functions of the Standard Observer and second corresponding tristimulus values using said third spectral curves and said first spectral curves; and

calibrating said digital camera in accordance with a relationship between said first tristimulus values and said second corresponding tristimulus values.

31. An apparatus for making a display surface uniform in brightness and neutral balance comprising:

optics capable of forming an image of said display surface;

an array sensor capable of converting said image into electrical signals, wherein said electrical signals are useable to produce digital image data that are corrected for non-uniform sensitivity of said array sensor elements; and

a controller, or a plurality of controllers operating in conjunction, capable of operating said array sensor to determine a spatial correction function for displaying said digital image by said display surface which enables uniformity of brightness and neutral balance across said display surface.

32. The apparatus according to claim 31 wherein when a plurality of controllers operate in conjunction said controllers are capable of communicating with each other through one of a network interface, a wireless transceiver, or a serial bus.

33. A system for improving color match between at least one page of a color signature and a reference comprising:

an imaging device capable of producing a digital color image representing one or more pages of a signature printed by an output device, wherein said imaging device is calibrated to provide image data in standard units;

a computer associated with said imaging device, said computer being capable of communicating with one or more other computers, wherein said computer has access, directly or indirectly, to memory comprising a model of the effects of position within said signature on color reproduction by said output device and said model is useable to predict or to improve color match between colors within said signature and said reference.