IL96816A - Apparatus and method for controlling operation of an image processing device. - Google Patents

Description

APPARATUS AND METHOD FOR CONTROLLING OPERATION OF AN IMAGE PROCESSING DEVICE nijinn ni'N1? τκοη n^iya mpi1? πϋ'κπ ιρππ SCITEX CORPORATION LTD.

C:10077 10Q77add.zev I-9OO6 27dec90 FIELD OF THE INVENTION The present invention relates to techniques for tone and color reproduction control in graphic arts.

BACKGROUND OF THE INVENTION Scanning methods are reviewed in R. K. olla>, Electronic Color Separation , R. K. Printing & Publishing, New York, 1988, the disclosure of which is incorporated herein by reference. The principles of color are explained in G. Wyszecki and W. S. Stiles, Color Science , Wiley & Sons, 1982, the disclosure of which is incorporated herein by reference.

Generally speaking, tone and color reproduction control in high quality graphic arts reproduction is still far from a science. This is particularly evident when a given acceptable result, already realized using given reproduction apparatus, is sought to be realized using other apparatus. In such cases, a high degree of expertise, combined with time, effort, expense and patience is required to calibrate the additional apparatus. The results are not always satisfactory.

Image creation systems typically comprise a computer with associated graphic software for generating digital representations of color images and/or modifying digital representations of color images, and a plotter or other color output device for transforming the digital representations into analog representations. The analog representation may be created on any suitable substrate, such as on a dia. If desired, e.g. in pre-press applications, the resulting dia can be scanned.

Examples of commercially available graphic software are Photoshop, by Adobe Systems Inc., Mountainview , CA, USA, usable in conjunction with the Mac II by Apple Computer Inc., USA; and PC Paintbrush Plus, by ZSoft, San Francisco, CA, USA, usable in conjunction with the IBM PC. Examples of commercially available plotters are 4cast, by DuPont, Wilmington, DE, USA, and the LVT Model 1620 digital image recorder by Light Valve Technology, Rochester, NY, USA.

SUMMARY OF THE INVENTION The present invention seeks to provide an improved method and apparatus for image processing.

The following terms as used in the present specification and claims should be construed in the following manner : Analog representation of a color image ; A representation of a color image which is perceivable by the human eye as a color image. The representation may appear upon a transparency, a photograph, a CRT display, a printed page, etc.

Digi tal representation of a color image : Any representation of a color image which is expressed in discrete symbols, such as numerical symbols. A common digital representation of a color image is a digital file comprising a plurality of numerical values corresponding to a plurality of pixels into which the color image has been divided, each such numerical value representing some aspect pertaining to the colored appearance of the corresponding pixel. , Subs trate ; Physical apparatus bearing or displaying an analog representation of an image, e.g. transparency, Cromalin (registered trademark), CRT display, photograph, offset or gravure print, surfaces suitable for painting on, etc.

Range of image processing apparatus ; The totality of color values which can be output by a printing machine.

Domain of image processing apparatus : The totality of color values which can be handled by the image processing apparatus. The domain is typically represented by eight bit coordinates for each of three color separation values. Using an appropriate scaling, the domain can represent any color space and all visible colors.

Image processing apparatus ; Apparatus which takes ¾s input a first representation of a color image (digital or analog) and converts it into a second representation thereof (analog or digital) Image creation system : Apparatus which creates an image internally or one which takes as input a representation of a color image and modifies it. Such a system can create the color image from geometrical shapes, can alter the shape and can select and/or modify the color of the color image.

Color reading apparatus ; Apparatus which inputs an analog representation of a color image and converts it to a digital representation or to an analog electrical representation thereof, e.g., ECSS, DECSS, colorimeters, spectrum analyzers, densitometers. Typically, the digital representation is expressed in a coordinate system such as XYZ , CMYK, RGB, etc.

Printing machine/device/ system ; output apparatus , recording apparatus etc . : Any apparatus which inputs a digital representation of a color image and converts it into an analog representation thereof. For example: conventional or direct digital proofing machines, plotters or color recorders which expose photographic materials, electrostatic printing systems employing powder colorants, color monitors, and color CRT displays .

Calibration : Adjusting image processing apparatus such that representations are produced in accordance to predetermined requirements.

Color value : A representation of a color, typically in a color coordinate system such as but not limited to RGB, L a b , XYZ coordinate systems and device dependent coordinate systems such as color head signals e.g. RGB, ink percentages e.g. CMYK, etc.

Colorant , ink , etc . : Any stimulant of the human eye's light energy receptors, including liquid colorants, powder colorants, photographic colorants, phosphors, etc. , Colorant values : A digital representation of the amount of a colorant which it is sought to use.

It is appreciated that any references to color, color images, color values, colorant values, etc. in the present specification are intended to include the instances of black and white as colors or color values, black and white images, black colorant and ink, etc.

RGB : red, green, blue. More generally, the term as used herein may refer to any color signals produced by a color reading device, An image processing system or a color printing device. In a color separation scanner, the term normally refers to the color separation signals of the scanner prior to processing thereof or after quasi log or other one dimensional transformation.

CMYK : cyan, magenta, yellow, black (colorants such as inks). More generally, the term as used herein refers to any signals which may serve as input for a color printing device.

There is thus provided, in accordance with a preferred embodiment of the present invention, a technique for controlling the operation of an image processing device having a first color coordinate system and including the steps of receiving a digital representation of a color image defined in a second color coordinate system, providing a transformation between the first color coordinate system and the second color coordinate system, employing the transformation to transform the digital representation of the color image into a transformed digital representation of the color image in the first color coordinate system and employing the image processing device to modify the transformed digital representation of the color image.

Additionally, in accordance with a preferred embodiment of the present invention, the digital representation is provided by an input device. The second color coordinate system is the coordinate system of the input device.

Furthermore, in accordance with a preferred embodiment of the present invention, the step of employing the transformation is performed by a device having the second color coordinate system. Alternatively, the step of employing the transformation is performed by the image processing device.

There is further provided, in accordance with a preferred embodiment of the present invention, an image processing device having a first color coordinate system including apparatus for receiving a digital representation of a color image defined in a second color coordinate system, transformation construction apparatus for providing a transformation between the first color coordinate system and the second color coordinate system and apparatus for employing the transformation to transform the digital representation of the color image into a transformed digital representation of the color image in the first color coordinate system. The image processing device is operative to modify the transformed digital representation of the color image.

Additionally, in accordance with a preferred embodiment of the present invention, the digital representation ½s provided by an input device.

Further, in accordance with a preferred embodiment of the present invention, the second color coordinate system is the coordinate system of the input device.

Finally, in accordance with a preferred embodiment of the present invention, the transformation construction apparatus form part of a device having the second color coordinate system.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: Fig. 1 is a general block diagram illustrating an image processing unit, a scanner and apparatus for calibrating the scanner to the image processing unit, the apparatus being constructed and operative in accordance with a preferred embodiment of the present invention; and Fig. 2 is a general block diagram illustrating use of the apparatus of Fig. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Image creation and processing systems may be used to merge or combine more than one color image into a single color image and\or to modify input color images. For example, it may be desired to create a color image comprising a first portion obtained by photographic techniques and subsequently read into the image processing system, preferably using conventional scanning techniques, and a second portion generated by the graphic software of the image processing system. Alternatively or in addition, it may be desired to use the graphic software of the image processing system to modify a digital representation of a photographic image or of any other color image generated externally of the image processing system.

Unfortunately, the coordinates used to define internally generated images, denoted here as creation system coordinates, are typically different than those used to define externally generated images, denoted here as scanner coordinates. For ' example, a RGB color value (0,0,10) in scanner coordinates might result in a first input color blue while producing an output of a second color blue in creation system coordinates. However, when combining internally and externally generated images, or when modifying an externally generated image within the graphic software, it is desired to match the two coordinate systems such that the RGB color value (0,0,10) represents the same color for the scanner input and the image processing unit.

A preferred method and apparatus for achieving one or both of the above objectives is shown and described herein. The apparatus and method shown and described herein have the particular advantage of automatically and generally without resorting to human judgement providing an output from the image processing system which generally resembles the input thereto, apart from the modifications or merge operations performed on the input by the image processing system. In this context, two analog representations resemble one another if a color reading device reading both representations will output substantially the same digital representation for both analog representations .

Reference is now made to Fig. 1 which illustrates calibration of an image processing system comprising a color reading device 732 , such as a scanner, means for modifying a digital representation of a color image, such as graphic software 75^ (Fig- 2 ) , and a color output device 726 , such as a plotter or other color output apparatus. The calibration enables an image read by the scanner 732 to be processed and to be subsequently output by the plotter 726 , substantially without causing distortion of the representation of the color image input to the scanner 732 , except for the intentional modifications performed thereupon by the image processing system.

As seen in Fig. 1 , a digital database 722 is input to, generated in, read from an analog image, or otherwise made available to an image processing unit 724 . The digital database 722 generally comprises a plurality of digital color values, defined in the color coordinate system of image processing unit 724 .

The database 722 typically comprises a digital file which may be generated by any suitable means, such as via graphic software, or alternatively may be input into the image processing system by any suitable communication method, such as via magnetic tape. Database 722 is output by color output apparatus 726, such as a 4cast plotter, commercially available from DuPont, on any suitable substrate 728, such as a transparency, thereby to provide an analog representation 730 corresponding to the digital representation 722 of the database. Preferably the substrate 728 should be of the same medium as the substrate which it is desired to use to bear the analog images 750 which it is intended to process (Fig. 2). By 'same medium' it is meant the same product. Thus, if it is intended to process using ektachrome substrates produced by Kodak Corporation of the USA, then ektachrome substrates are preferably used for substrate 728.

Analog representation 730 is read by color reading device 732, which may comprise any suitable device such as the Smart Scanner, commercially available from Scitex Corporation, Herzlia, Israel. Scanner 732 produces a digital representation 73^ ' whose color values are defined in the coordinate system of scanner 732. , Digital representation 73^ of the database and the original digital representation 722 of the database are both then input into transformation construction apparatus 736. Transformation construction apparatus 736 is operative to construct a transformation from the digital representation 73^ to the digital representation 722 and to output this transformation in any suitable form. The transformation is, effectively, a transformation from the color coordinate system of the scanner 732 to that of the image processing unit 724 combined with the output device 726 .

Preferably, the transformation is output and stored as a LookUp Table (LUT) 738 . The LUT 738 may subsequently be loaded onto scanner 732 or onto suitable computing means, such as an IBM PC or a suitable module that may exist in the image processing unit 724 , and may then be used as described hereinbelow with reference to Fig. 2 .

Transformation construction apparatus 736 i"s preferably constructed and operative in accordance with the function construction principles shown and described in Applicant's Israel Patent Application 93274 , the disclosure of which is incorporated herein by reference.

The plurality of digital color values of database 722 typically represents the color space in which the operator of the image processing apparatus works. It typically has a predetermined pattern, typically comprising patches of color, which typically has at least a minimum density of data (digital color values) in every location of interest. The predetermined pattern may, for example, be a generally even distribution throughout generally the entirety of the producible color space. If certain volumes of the color space are more important to the operator, then the operator may define more color patches in that volume to allow a more accurate represenation of the volume.

Specifically, the operator may produce his desired database 722 as follows: 1 . An initial database of patches is produced wherein the colors of the patches have a subset of possible three dimensional eight bit digital color values, where a typical subset is defined as the following combinations of Red (R) , Green (G) and Blue (B) : R = n*50 G = m*50 (1) B = p*50 where n, m and p are the entirety of integer values between 0 and 5, inclusive. This produces 216 patches. 2. The initial database is output, to a substrate such as film, by the output device 726, thereby producing an analog output. 3. The operator visually selects on the analog output those patches of the initial database that are included in the color space volume that he wishes to be more accurately represented in his desired database 722 and indicates his selections to image processing unit 724. For example, one selected patch might be the patch that was created by: R = 50, G = 100, B = 150.

. For each selected patch, a plurality of .patches are created which are close to it in color. For example, eight more colors might be created which are in the color volume around the selected example color by taking the entirety of combinations of: R = n*25 + 50 G = m*25 + 100 (2) B = p*25 + 150 where n, m and p are either 1 or -1.

An alternative method for constructing a database with a desired distribution is described and claimed in Applicant's previously noted Israel Patent Application No. 93274 .

Use of the calibrated apparatus of Fig. 1 will now be described, with reference to Fig. 2 . There is shown an analog representation 750 of a color image which it is desired to process, using the image processing system of Fig. 1 which comprises graphic software 754 or any other suitable means for producing or modifying representations of color images, including combining or merging means 756 for combining more than one representation of color images into a single representation of a single, combined color image, as well as the scanner 732 and the output device 726 .

As shown, the analog representation 7 0 s read by a color reading device 732 , such as a Smart Scanner, commercially available from Scitex Corporation, which is substantially identical to scanner 732 of Fig. 1 , and which is loaded with LUT 738 of Fig. 1 . Alternatively, the color reading device 732 may not be loaded with LUT 738 nor with any representation of the transformation constructed by transformation construction means 73 of Fig. 1 . Instead, the output of color separation unit 752 of the scanner 732 , normally in the form of RGB separations or quasi log of RGB separations of the scanner, may be input into transformation operation means 758 . Transformation operation means 758 may comprise any suitable computer, such as an IBM PC or a module of the image processing system 7 4 , and is operative to transform the input thereto in accordance with LUT 738 constructed by transformation computation means 736 of Fig. 1 .

The transformed output of scanner 732 , typically comprising a digital file 7 Ο in the color coordinate system of the image processing system 724, is input to image processing system 724, typically comprising graphic software 754 and/or merging means 756. The digital file 760 may be modified by graphic software 754 and/or it may be merged with another digital image 762 by merging means 756. The merged image may, if desired, be modified by graphics software 754. The final modified and/or merged digital representation 764 is then transformed into an analog image 766, using output device 726 of Fig. 1. The portions of analog image 766 from inital image 750 which did not undergo the modification described hereinabove will be substantially identical in appearance to the initial image 750.

Any suitable method may be employed for merging at least a portion of the digital file 76Ο with at least a portion of digital image 762. Apparatus and methods for merging color images are described and claimed in Applicant's Israel Application No. 93^93. the disclosure of which is incorporated herein by reference.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow :

Claims (8)

1. A technique for calibrating a color processing device operating in conjunction with color reading apparatus, the technique comprising: receiving a first digital representation of a first color image; providing an analog representation thereof; employing color reading apparatus to provide a second digital representation of the analog representation of said first color image; comparing the second digital representation of said first color image with the first digital representation thereof, thereby to provide a transformation therebetween; and employing said transformation to modify a digital representation of at least a second color image provided by said color reading apparatus to said color processing device.

2. A technique according to claim 1 wherein said analog representation of said first color image is provided by an output device.

3. Apparatus for calibrating a color processing device operating in conjunction with a color reading apparatus comprising : means for receiving a first digital representation of a first color image; 96816/2 means for providing an analog representation thereof; means for employing a color reading apparatus to provide a second digital representation of the analog representation of said first color image; means for comparing the second digital representation of said first color image with the first digital representation thereof, thereby to provide a transformation therebetween; and means for employing said transformation to modify a digital representation of at least a second color image provided by said color reading apparatus to said color processing device.

4. Apparatus according to claim 3 wherein said means for providing include an output device.

5. Apparatus according to claim 3 and wherein said means for employing said transformation include a LUT.

6. A technique substantially as shown and described hereinabove.

7. A technique substantially as illustrated in any of the drawings.

8. Apparatus substantially as shown and described hereinabove. For the Applicant, Sanford T. Colb & Co. C:10077