WO1996035291A1 - Systeme servant a corriger les couleurs dans un systeme imageur electronique - Google Patents

Systeme servant a corriger les couleurs dans un systeme imageur electronique Download PDF

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Publication number
WO1996035291A1
WO1996035291A1 PCT/US1996/004947 US9604947W WO9635291A1 WO 1996035291 A1 WO1996035291 A1 WO 1996035291A1 US 9604947 W US9604947 W US 9604947W WO 9635291 A1 WO9635291 A1 WO 9635291A1
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WO
WIPO (PCT)
Prior art keywords
color
cast
image
methodologies
scanner
Prior art date
Application number
PCT/US1996/004947
Other languages
English (en)
Inventor
Eric W. Higgins
James A. Boyack
Original Assignee
Polaroid Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Polaroid Corporation filed Critical Polaroid Corporation
Priority to KR1019960707595A priority Critical patent/KR970704290A/ko
Priority to JP8533318A priority patent/JPH10503072A/ja
Priority to EP96910801A priority patent/EP0769233A1/fr
Publication of WO1996035291A1 publication Critical patent/WO1996035291A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/46—Colour picture communication systems
    • H04N1/56—Processing of colour picture signals
    • H04N1/60—Colour correction or control
    • H04N1/6011—Colour correction or control with simulation on a subsidiary picture reproducer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/46—Colour picture communication systems
    • H04N1/56—Processing of colour picture signals
    • H04N1/60—Colour correction or control

Definitions

  • This invention in general, relates to the field of electronic imaging devices and, more particularly, to apparatus and methods for use in such devices for editing tone range and correcting for color errors.
  • Objects that are neutral in color that is, those which reflect equal amounts of an adopted set of primary colors, will appear neutral gray when illuminated by a source that is spectrally flat.
  • a neutral gray object illuminated by a spectrally flat source such as noontime sunlight, which has a uniform spectral power distribution, will appear more or less neutral to an observer.
  • a light source differs from neutral, it is said to have a "color cast” since its spectral content is no longer flat with wavelength, but rather, contains more of one "color” than another.
  • color cast occurs in the electronic scanning and display of images.
  • color photographic materials reflection prints or transparencies
  • displaying the scanned image via a monitor after applying a color transform of some sort the displayed image often appears with an objectionable color cast which is bothersome because it is unnatural in appearance.
  • color casts can be attributed to a variety of sources including, but not limited to, scene illumination conditions during photographic exposure, variation in the characteristics of the photographic materials themselves, ambient temperature conditions, or variations in subsequent chemical processing.
  • Color copiers may employ steps similar to those above or various combinations of them.
  • Image processing software often provides for user adjustment of color cast by way of manual control over color content through the use of color sliders for R, G, B content.
  • color sliders for R, G, B content.
  • Such controls can be cumbersome and as problematical as they are beneficial.
  • the invention is related to electronic color processing of images in the form of electronic signals and, in particular, to systems which are not wholly automatic but involve some operator selection. It is applicable to electronic scanners used to scan photographic or other materials, photofmishing, electronic still cameras, video cameras, video or still picture image-editing software, or in the related arts. It may be used with systems using three or more color signals (e.g. RGB or CMYK). Although the preferred embodiment involves the use of digital signals, analog signal processing to perform these operations could also be implemented. Regardless of the signal source, all aspects of the invention involve the use of a color display which is viewed by an operator.
  • the inventive system operates to remove color casts or color balance errors from images.
  • the system consists of three main parts: a set of cast-prediction operators which operate on the source image data and coarse device profile data, a preview mechanism whereby an image can be displayed to the operator on a calibrated color display, and a mechanism for selecting between candidate casts computed by the cast-prediction operators - which are applied to the images and displayed to the user for evaluation.
  • the use of subsampled images for image preview and cast-removal computation is recommended, but not required.
  • the operator obtains a source image and presents it to the system, along with the coarse device profile for the image acquisition system and a device profile for the display monitor.
  • the system computes equivalent log-scene exposures (e.g. Red exposure, Green Exposure, Blue Exposure) for each pixel in the image.
  • the cast prediction operators compute a color cast from the log-scene exposure images using knowledge derived from the image data and the known exposure balance (color balance or cast) of a neutral object in the scene — which was provided as part of the coarse profile data accompanying the image.
  • the cast predictions from each of the operators, now represented by a log exposure triplet e.g., R, G, B exposure
  • the operator selects a cast prediction for preview.
  • the image data is processed through the color processing system the operator normally uses to transform the input image data for display on the monitor, with modifications such that the selected color cast correction is applied.
  • cast correction may be introduced by adding an offset to each channel before sending the data to the color processor to compute an image for rendering on the display.
  • an operator repeats the color transform and preview operation for each of the cast predictions, and then selects the cast prediction having the preferred appearance. Additional cast correction could be performed in exceptional cases using conventional means, beginning with the closest prediction from the above system.
  • Fig. 1 is a diagrammatic perspective view of an electronic imaging system in which the present invention is embodied
  • Fig. 2 shows a flow diagram for an embodiment of the invention in the form of a transparency scanner and associated components which implement the cast removal methodology of the invention and demonstrates how preview and cast- removal modules of the invention interact with other system components;
  • Fig. 3 is a flow diagram for the cast removal module of Fig. 2, showing the interaction of the cast computation, preview, and cast selection mechanisms;
  • Fig. 4 is a flow diagram of the color cast prediction module of the invention.
  • Fig. 5 shows a graphical user interface by which the image preview and cast selection mechanism can be operated as part of an image-editing workstation.
  • the scanner consists of a transport light source, color CCD linear array detector, a transport mechanism, a preview memory, and a color transform mechanism.
  • Output from the scanner is digital data intended for display on a color monitor with output characteristics similar to the Apple 13 inch color monitor, manufactured by Apple Computer of Cupertino, California.
  • This system is designed to provide high quality digital color images from a wide variety of photographic negative and transparency materials. Further, it is designed to be used by relatively unskilled operators who may or may not have significant knowledge of color reproduction systems, and need rapid scanning of their images.
  • the major application for the scanner is in the desktop publishing application where the scanner is attached to a personal computer used for image editing and display. As such, the scanner is controlled by and provides output data to host application software executing on a PC (e.g. Adobe Photoshop by Adobe Systems, Incorporated).
  • FIG. 1 shows an image-editing workstation 20 embodying a preferred form of the invention.
  • Components of the workstation 20 comprise a computer 22 used to perform operations on image data and present a user with a graphical interface in the form of dialogs on a color monitor 24, which is preferably calibrated. Color monitor 24 is also used for image preview and display operations.
  • a pointing device 28 and keyboard 26 facilitate operator interaction with other components of workstation 20.
  • a disk drive 36 can be used for input or output of image files to or from a storage disk 34 or the like. Input signals can also originate from a digital still or motion video camera 30, but preferably originate from a transparency scanner 32.
  • the work station 20 allows an operator to place the scan media in the scanner, specify the material to be scanned (e.g., color negative)along with the scan resolution and output size.
  • a low resolution preview scan is performed and displayed to the user after having been color processed for viewing on the calibrated monitor.
  • the user can then perform adjustments on the scan parameters (e.g., sharpening level, color cast removal, brightness, cropping,...) while viewing an interactive image preview showing the results of the adjustments, then initiate a final scan.
  • a high resolution scan is then performed and the data from the CCD array is immediately processed through the color processor and sent to the host application.
  • FIG. 2 is a block diagram showing major components of the invention as it resides in workstation 20 and is generally designated as a system 50.
  • system 50 comprises photographic negative image sampling module 52.
  • Module 52 includes a light source 54 and a sensor 58 in the form of a CCD array.
  • the material being scanned in this case a color negative, is designated at 56.
  • Output signals are generated from CCD array 58 as the negative 56 is scanned.
  • the output signals consist of three analog signals, one each for three primaries: red, green, and blue. The output signals are approximately linear with respect to optical transmittance of the negative being scanned, in each color channel.
  • the output of the sampling hardware is taken as input to the digitization block 60, which consists of an adjustable analog gain stage 62 and an analog-to-digital converter 64.
  • the analog gain stage 62 allows adjustment of the signal input to the analog-to-digital converter 64, which converts the analog signals to quantized digital signals having discrete levels.
  • the output of the digitization stage can be directed to two modules, depending on the operational mode of the scanner. During preview mode, the output is directed to the input of a preview and cast correction module 72. Alternately, when in final scan mode, the output is directed to the input of a color processor 74.
  • a control line 90 and mode switch 70 direct the signal from the analog-to-digital converter 64 toward the cast preview and removal module 72 or color processor 74 based on the current selected scan mode.
  • the outputs of the cast preview and removal module 84, 86, and 88, respectively, are directed to the light source 54, analog gain stage 62 and color processor 74, respectively.
  • the signals are gain or offset signals appropriate for adjusting the corresponding subsystems to achieve the desired cast removal.
  • data from the analog-to-digital converter 64 are processed through the color processor 74 using input from the cast preview and removal module 72 .
  • the resultant image data can then be sent to a number of outputs 76 including host application 78 (e.g., Adobe Photoshop) running on the host computer 22, the color display monitor 80, or a storage file 82.
  • host application 78 e.g., Adobe Photoshop
  • Fig. 3 is a block diagram showing in more detail cast preview and removal module 72.
  • Input to module 72 is stored in digital memory 74.
  • the contents of memory 74 can be read as input to three modules, depending on the mode of operation of the cast preview and removal module 72.
  • the cast predictions are determined by the cast prediction module 76, operating on the data in the preview memory buffer 74 and stored in a memory buffer 78 for later use.
  • an exposure shift is computed by use of a scene analysis module 92 operating on the contents of the preview buffer 74.
  • the operation consists of creating a luminance signal from a color signal 94 and running the scene analysis processor 96.
  • the output of processor 96 is a signal which is applied equally to all three color channels, and will not introduce or remove a color cast.
  • Different cast prediction methodologies are carried out in block 76 and stored in, respectively, blocks 80 or 82 or 84 or 86 in memory 78.
  • the results of the cast prediction methodologies are selectable by a selection mechanism 90 via operator intervention and the results are combined with the signal from the scene analysis module 92 at a junction 100.
  • the combined signal is sent to a color processor 102 and/or to a gain partitioning module 106.
  • the gain partitioning module 106 sends a signal to the light source 54, gain stage 62 and/or color processor 74.
  • the contents of the preview buffer 74 is processed through the color processor 102 with input from junction 100 and the resulting image displayed on color monitor 104 for cast judgment by the operator.
  • Cast prediction module 76 will now be described with reference to Fig. 4.
  • the contents of preview buffer 74 are processed through a color processor 200 to form a representation of scene exposure, which is stored in a memory buffer 202.
  • Cast operators 206, 208, 210 and 212 take the contents of this buffer as input, and each output a cast signal which is stored in a corresponding memory buffer location 80,82,84,86, respectively, in the cast memory 78.
  • Fig. 5 shows a graphical user interface with which a user interacts in practicing the invention.
  • An operator interaction dialog 120 is used in the preferred embodiment. It consists of a dialog box presented to the user on the color monitor 24 by computer 22.
  • Region 122 is a color image display into which is mapped the contents of the preview buffer 74 after processing by color processor 102 operating in the display mode of the cast preview and removal module 72.
  • a cast selection mechanism 124 consisting of four buttons, 126,128,130,132, each corresponding to a cast memory location (80,82,84,86) in the cast buffer 78.
  • Below the selection mechanism is a button for initiating a final scan 140, which sends input to the mode switch 70.
  • Region tool 142 allows the operator to select a region in the memory buffer 74 on which to perform the cast computations corresponding to the enclosed region in the preview image 122 using the keyboard 26 or pointing device 28.
  • scanner 32 is first configured for preview scanning.
  • the gain of the analog gain stage 62 (a linear amplifier) is set such that the minimum density (film base density) for a negative of the selected film type produces an input signal to the analog to digital converter 64 which is mapped to digit 1024 (out of 1024). Data for this adjustment is contained in a device profile for the scanner/negative combination selected by the user before initiating the scan. As CCD 58 output voltage is nearly linear with respect to incident light, the digital counts from A/D converter 64 will correspond to negative optical transmittances.
  • the low resolution preview scan is made, and a resulting RGB 10-bit image stored in the preview buffer 74 shown in Figure 3.
  • the image data are converted from digital count to scene log exposure and stored in a computer memory buffer.
  • the following operations are performed on the log exposure data to predict candidate color casts.
  • the first method is to perform no computation and report a color cast of zero red, zero green and zero blue exposure.
  • the white point cast prediction method assumes that the brightest object in the scene is a specular reflection of the illumination source off a neutral object.
  • the gray world cast prediction method is based on the approximation that for a large number of scenes, the scene exposure in the three channels red, green, and blue when summed over the image area, will be equal.
  • the operation is to simply determine the mean of all pixels in each of the three channels. That is:
  • Rij, Gij, Bij are the red, green, and blue exposures of the ij'th pixel
  • nx is the height of the selected region
  • ny is the width, specified in low resolution pixels.
  • the bright pastel cast prediction method is based on the observation that a white point determined from a specular highlight (as in the White Point method above) will be incorrect due to the object reflectance not being neutral. For example, a red Christmas-tree ball might be the brightest point found in the image, but certainly is not neutral and will cause a poor cast estimate.
  • the bright pastel method operates by using the white point determined above, and averages together all pixels with exposure within a constant factor PASTELRANGE (e.g. 4) of the white having inter-channel color difference less than another factor (e.g. 0.15 logE) a) determine the exposure of the brightest pixel using the White Point method described above, then determine the minimum brightness threshold.
  • PASTELRANGE e.g. 4
  • another factor e.g. 0.15 logE
  • a preferred method for facilitating this selection is to generate an image preview from each of the four candidates — which represents the final cast the operator will observe on the color monitor when the selected methods are applied to the final scan operation, regardless of how the cast-removal operation is actually implemented.
  • the preferred embodiment is to provide the user a set of "buttons" to select a cast (method) and update the color monitor rapidly to reflect the change in the image.
  • the color monitor used for the preview step must be adjusted prior to use such that the color of a neutral object in the scene (no color cast) has the appearance the user is attempting to achieve by the reproduction.
  • the operator is assumed to have calibrated the display monitor in such a way that the Apple 13 inch Color Monitor device profile adequately represents the color monitor. This calibration can be performed using readily available tools (e.g. Knoll Gamma tool supplied with Adobe Photoshop).
  • the contents of the preview buffer memory is processed through the color processor using the scanner/negative profile appropriate for the negative currently being scanned.
  • the profile actually passed to the color processor has been modified to incorporate the cast change selected by the operator in the previous step (2 above).
  • the resulting image is displayed on the color monitor for the operators judgment. This operation is repeated under the user control for all selections of cast (removal method).
  • the operator Having selected the appropriate cast removal, the operator initiates a final scan.
  • the scanner is reconfigured to pass the output(s) of the A/D converter(s) directly to the color processor unit which has been configured as above to account for the selected cast change. If the cast change is large, the change may be partitioned between the modified scanner/negative profile and the analog gain stage ahead of the A/D converted to reduce data loss.
  • a high-resolution scan is then made, processed through the color processor, and output to the host software application.
  • the invention may also be implemented in consumer camcorders or the like.
  • Consumer camcorders use a slightly different approach, as the main problem is changing illuminant color temperature. Most operate by attempting to determine a white object in the scene, and then deriving color cast from the cast of the white point. The capture circuitry is then recalibrated "on-the-fly" as photography continues. (AGC-automatic gain control, and auto white point control (corrects for difference in lighting color temperature))
  • Color copiers may employ variations of the techniques described above.
  • Image-processing software allows user adjustment of color cast — Adobe Photoshop "Variations" plug in for example.
  • a user is given controls (R,G,B sliders for example) and can apply a specific cast change to an image.

Abstract

L'invention décrit un système servant à prévoir et à corriger des reflets de couleur dans des images numériques. Elle présente un moyen de calculer (prévoir) des reflets de couleur candidats à partir de données-image lues par scanner, ainsi qu'un moyen de sélectionner, parmi cet ensemble de reflets candidats, le reflet le plus acceptable, sur une base interactive.
PCT/US1996/004947 1995-05-02 1996-04-11 Systeme servant a corriger les couleurs dans un systeme imageur electronique WO1996035291A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
KR1019960707595A KR970704290A (ko) 1995-05-02 1996-04-11 전자 화상 시스템 내의 색 교정용 장치
JP8533318A JPH10503072A (ja) 1995-05-02 1996-04-11 電子画像装置の色補正に使用する装置
EP96910801A EP0769233A1 (fr) 1995-05-02 1996-04-11 Systeme servant a corriger les couleurs dans un systeme imageur electronique

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US43298695A 1995-05-02 1995-05-02
US08/432,986 1995-05-02

Publications (1)

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WO1996035291A1 true WO1996035291A1 (fr) 1996-11-07

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PCT/US1996/004947 WO1996035291A1 (fr) 1995-05-02 1996-04-11 Systeme servant a corriger les couleurs dans un systeme imageur electronique

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EP (1) EP0769233A1 (fr)
JP (1) JPH10503072A (fr)
KR (1) KR970704290A (fr)
CA (1) CA2192104A1 (fr)
WO (1) WO1996035291A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999046928A1 (fr) * 1998-03-12 1999-09-16 Heidelberger Druckmaschinen Aktiengesellschaft Procede de selection automatique de calibrages de couleurs
EP1278373A2 (fr) * 2001-07-17 2003-01-22 Eastman Kodak Company Caméra avec suggestion de correction et méthode
EP1280336A2 (fr) * 2001-07-17 2003-01-29 Eastman Kodak Company Caméra avec révision d'image et méthode associée
EP1280340A2 (fr) * 2001-07-17 2003-01-29 Eastman Kodak Company Caméra et méthode reprennant une prise de vue corrigée

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP7066518B2 (ja) * 2018-05-17 2022-05-13 キヤノン株式会社 プログラム及び制御方法

Citations (3)

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Publication number Priority date Publication date Assignee Title
US4958221A (en) * 1988-11-08 1990-09-18 Minolta Camera Kabushiki Kaisha Digital color copying machine comprising a test mode for making a color adjustment
JPH02275938A (ja) * 1989-04-18 1990-11-09 Fuji Xerox Co Ltd フイルム画像読取装置におけるカラーキャスト補正方式
WO1992005470A1 (fr) * 1990-09-17 1992-04-02 Eastman Kodak Company Reduction en mode interactif avec l'utilisateur des defaillances d'equilibrage du decor

Patent Citations (3)

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Publication number Priority date Publication date Assignee Title
US4958221A (en) * 1988-11-08 1990-09-18 Minolta Camera Kabushiki Kaisha Digital color copying machine comprising a test mode for making a color adjustment
JPH02275938A (ja) * 1989-04-18 1990-11-09 Fuji Xerox Co Ltd フイルム画像読取装置におけるカラーキャスト補正方式
WO1992005470A1 (fr) * 1990-09-17 1992-04-02 Eastman Kodak Company Reduction en mode interactif avec l'utilisateur des defaillances d'equilibrage du decor

Non-Patent Citations (1)

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PATENT ABSTRACTS OF JAPAN vol. 15, no. 41 (P - 1160) 31 January 1991 (1991-01-31) *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999046928A1 (fr) * 1998-03-12 1999-09-16 Heidelberger Druckmaschinen Aktiengesellschaft Procede de selection automatique de calibrages de couleurs
US6724422B1 (en) 1998-03-12 2004-04-20 Heidelberger Druckmaschinen Ag Method for automatically selecting color calibrations
EP1278373A2 (fr) * 2001-07-17 2003-01-22 Eastman Kodak Company Caméra avec suggestion de correction et méthode
EP1280336A2 (fr) * 2001-07-17 2003-01-29 Eastman Kodak Company Caméra avec révision d'image et méthode associée
EP1280340A2 (fr) * 2001-07-17 2003-01-29 Eastman Kodak Company Caméra et méthode reprennant une prise de vue corrigée
EP1278373A3 (fr) * 2001-07-17 2004-03-17 Eastman Kodak Company Caméra avec suggestion de correction et méthode
EP1280336A3 (fr) * 2001-07-17 2004-03-17 Eastman Kodak Company Caméra avec révision d'image et méthode associée
EP1280340A3 (fr) * 2001-07-17 2004-03-17 Eastman Kodak Company Caméra et méthode reprennant une prise de vue corrigée
US6930718B2 (en) 2001-07-17 2005-08-16 Eastman Kodak Company Revised recapture camera and method
US7616248B2 (en) 2001-07-17 2009-11-10 Eastman Kodak Company Revised recapture camera and method
US8934043B2 (en) 2001-07-17 2015-01-13 Intellectual Ventures Fund 83 Llc Revised recapture camera and method

Also Published As

Publication number Publication date
EP0769233A1 (fr) 1997-04-23
CA2192104A1 (fr) 1996-11-07
KR970704290A (ko) 1997-08-09
JPH10503072A (ja) 1998-03-17

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