Color calibration of color image rendering devices

• US 9,894,340 B2
• Filed: 12/02/2016
• Issued: 02/13/2018
• Est. Priority Date: 08/31/2005
• Status: Active Grant

• Current Assignee: RAH Color Technologies LLC
• Original Assignee: RAH Color Technologies LLC
• Inventors: Holub, Richard A.
• Primary Examiner(s): NGUYEN, HAU H
• Application Number:
  US15/368,022
• Publication Number:
  US 20170085852A1
• Time in Patent Office: 438 Days
• 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. A method for detecting color differences between a source digital image and a reproduction by a rendering device of said source digital image, wherein said method is operable in a computer that communicates with said rendering device and comprises the steps of:

providing a rendering, upon a display surface associated with said rendering device, of one or more images stored in memory of said computer, each of said one or more images comprising one or more colors present identically at a plurality of spatial positions;

determining spatial variations of said each of said colors at said plurality of spatial positions within the rendering of each of said one or more images based upon measurements of spatial non-uniformity of the rendering upon said display surface;

producing upon said display surface a reproduction of said source digital image;

capturing a digital image of said reproduction of said source digital image;

computing one or more histograms from each of said source digital image and said digital image of said reproduction of said source digital image;

comparing corresponding ones of said one or more histograms of said each of said source digital image and said digital image of said reproduction of said source digital image from said computing step to determine color differences that are not due to said spatial non-uniformity of rendering upon said display surface by said rendering device; and

correcting said spatial non-uniformities of rendering and said color differences that are not due to said spatial non-uniformity of rendering to provide another reproduction of said source digital image, by said rendering device, that matches the colors of said source digital image within a criterion for color error.

2. The method according to claim 1 wherein said one or more histograms enable determination of said color differences that are not due to spatial non-uniformity of rendering independently of the spatial resolution of said source digital image and said captured digital image of said reproduction of said source digital image.

3. The method according to claim 2 further comprising the step of cross-correlating said corresponding ones of said one or more histograms of each of said source digital image and said digital image of said reproduction of said source digital image to determine said color differences that are not due to spatial non-uniformity of rendering.

4. The method according to claim 1 wherein at least said source digital image and said captured digital image are in device-independent units, each of said rendering step and said producing step further comprise the step of converting each of said colors into codes for controlling image reproduction by said rendering device, and said capturing step further comprises the step of converting codes generated by an image capture device into device independent color values.

5. The method according to claim 4 wherein said converting step converts between device codes and device independent color values using a multidimensional transformation in combination with tonal transfer curves for each of a plurality of channels of said rendering device, and at least said tonal transfer curves are based upon a calibration specific to said rendering device.

6. The method according to claim 1 wherein said step that comprises correcting said spatial non-uniformity of rendering modifies at least the tonal transfer in each color channel of said rendering device for each pixel across said display surface.

7. The method according to claim 6 wherein said pixel represents an average of a group of pixels on said display surface.

8. The method according to claim 6 wherein said step that comprises correcting said spatial non-uniformity of rendering employs interpolation in providing corrections for spatial non-uniformity of rendering upon said display surface.

9. The method according to claim 1 wherein said step that comprises correcting said color differences that are not due to said spatial non-uniformity of rendering computes a color-to-color′

transform to be used in combination with a multidimensional transformation that converts device-independent color values representing said source digital image into device codes for controlling rendering by said device.

10. The method according to claim 9 wherein said combination is implemented by concatenating said color-to-color’

transform with said multidimensional transformation that converts device-independent color values into device codes.

11. The method according to claim 1 wherein said rendering device is one of a printer or a video monitor.

12. A method for detecting color differences between a source digital image and a reproduction by a rendering device of said source digital image, wherein said method is operable in a computer that communicates with said rendering device and comprises the steps of:

providing a rendering, upon a display surface associated with said rendering device, of one or more images stored in memory of said computer;

measuring spatial non-uniformity of said rendering upon said display surface by said rendering device;

rendering upon said display surface a reproduction of said source digital image, wherein said reproduction is corrected for said spatial non-uniformity of said rendering measured by said measuring step;

capturing a digital image of said reproduction of said source digital image;

producing one or more histograms from each of said source digital image and said digital image of said reproduction of said source digital image;

comparing corresponding ones of said one or more histograms of said each of said source digital image and said digital image of said reproduction of said source digital image from said producing step to determine color differences; and

correcting said spatial non-uniformities of rendering and said color differences to provide another reproduction of said source digital image, by said rendering device, that matches the colors of said source digital image within a criterion for color error.

13. A method for detecting color differences between a source digital image and a reproduction by a rendering device of said source digital image, wherein said method is operable in a computer that communicates with said rendering device and comprises the steps of:

providing a rendering, upon a display surface associated with said rendering device, of one or more images stored in memory of said computer;

measuring spatial non-uniformity of said rendering upon said display surface by said rendering device;

rendering upon said display surface a reproduction of said source digital image;

capturing a digital image of said reproduction of said source digital image;

producing one or more histograms from each of said source digital image and said digital image of said reproduction of said source digital image, in which said one or more histograms produced from said source digital image are modified to account for said spatial non-uniformity of rendering measured by said measuring step;

comparing corresponding ones of said one or more histograms of said each of said source digital image and said digital image of said reproduction of said source digital image from said producing step to determine color differences; and

correcting said spatial non-uniformities of rendering and said color differences to provide another reproduction of said source digital image, by said rendering device, that matches the colors of said source digital image within a criterion for color error.

14. A non-transitory, computer-readable medium encoding software executable by a computer for detecting color differences between a source digital image and a reproduction by a rendering device of said source digital image, said software comprising:

one or more programs for enabling a rendering, upon a display surface associated with said rendering device, of one or more images stored in computer memory, each of said one or more images comprising one or more colors present identically at a plurality of spatial positions;

one or more programs for determining spatial variations of each of said colors at said plurality of spatial positions across said display surface within the rendering of each of said one or more images based upon measurements of spatial non-uniformity of the rendering upon said display surface;

one or more programs for producing upon said display surface a reproduction of said source digital image;

one or more programs for capturing a digital image of said reproduction of said source digital image;

one or more programs for computing one or more histograms from each of said source digital image and said digital image of said reproduction of said source digital image;

one or more programs for comparing corresponding ones of said one or more histograms of said each of said source digital image and said digital image of said reproduction of said source digital image to determine color differences that are not due to said spatial non-uniformity of rendering upon said display surface by said rendering device; and

one or more programs that correct said spatial non-uniformities of rendering and said color differences that are not due to said spatial non-uniformity of rendering to provide another reproduction of said source digital image, by said rendering device, that matches the colors of said source digital image within a criterion for color error.

15. The non-transitory, computer-readable medium according to claim 14 wherein said one or more histograms enable determination of said color differences that are not due to spatial non-uniformity of rendering independently of the spatial resolution of said source digital image and said captured digital image of said reproduction of said source digital image.

16. The non-transitory, computer-readable medium according to claim 15 wherein said determination of said color differences that are not due to spatial non-uniformity of rendering employs cross-correlation between said corresponding ones of said one or more histograms of each of said source digital image and said digital image of said reproduction of said source digital image.

17. The non-transitory, computer-readable medium according to claim 14 wherein at least said source digital image and said captured digital image are in device-independent units, said one or more programs for enabling a rendering and said one or more programs for producing perform conversion of said one or more colors into codes for controlling image reproduction by said rendering device, and wherein said one or more programs for capturing performs conversion of codes generated by an image capture device into device independent color values.

18. The non-transitory, computer-readable medium according to claim 17 wherein said conversion between device codes and device independent color values use a multidimensional transformation in combination with tonal transfer curves for each of a plurality of channels of said rendering device, in which at least said tonal transfer curves are based upon a calibration specific to said rendering device.

19. The non-transitory, computer-readable medium according to claim 14 wherein one of said one or more programs that provide color reproductions of source digital images corrects for said non-uniformity of rendering by modifying at least the tonal transfer in each color channel of said rendering device for each pixel across said display surface.

20. The non-transitory, computer-readable medium according to claim 19 wherein said pixel represents an average of a group of pixels on said display surface.

21. The non-transitory, computer-readable medium according to claim 19 wherein said program that corrects for said spatial non-uniformity of rendering employs interpolation in providing corrections for spatial non-uniformity of rendering upon said display surface.

22. The non-transitory, computer-readable medium according to claim 14 wherein one of said one or more programs that provide color reproductions of source digital images corrects said color differences that are not due to said spatial non-uniformity of rendering by computing a color-to-color′

transform to be used in combination with a multidimensional transformation that converts device-independent color values representing said source digital image into device codes for controlling rendering by said device.

23. The non-transitory, computer-readable medium according to claim 22 wherein said combination is implemented by concatenating said color-to-color’

transform with said multidimensional transformation that converts device-independent color values into device codes.

24. The non-transitory, computer-readable medium according to claim 14 wherein said rendering device is one of a printer or a video monitor.

25. The non-transitory, computer-readable medium according to claim 14 wherein said rendering device is a printing press and said digital image of said reproduction of said source digital image is captured by an imaging colorimeter and communicated to a computer associated with said printing press.

26. The non-transitory, computer-readable medium according to claim 25 wherein said computer associated with said printing press communicates a color-to-color′

transform over a network to one or more other computers to enable matching a reproduction of said source digital image by at least one rendering device associated with each of said one or more other computers with said reproduction of said source digital image by said printing press.

27. The non-transitory, computer-readable medium according to claim 25 wherein said computer associated with said printing press stores data of press color reproduction performance for use in refining a model of spatial dependencies of rendering by said printing press.

28. The non-transitory, computer-readable medium according to claim 27 wherein said model enables an operator to preview one or more arrangements of pages within an imposition.