GB2050751A - Image-reproduction apparatus - Google Patents
Image-reproduction apparatus Download PDFInfo
- Publication number
- GB2050751A GB2050751A GB8016963A GB8016963A GB2050751A GB 2050751 A GB2050751 A GB 2050751A GB 8016963 A GB8016963 A GB 8016963A GB 8016963 A GB8016963 A GB 8016963A GB 2050751 A GB2050751 A GB 2050751A
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- GB
- United Kingdom
- Prior art keywords
- colour
- signal
- signals
- look
- corrected
- Prior art date
- Legal status (The legal status 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 status listed.)
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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
- H04N1/6027—Correction or control of colour gradation or colour contrast
-
- 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
- H04N1/6016—Conversion to subtractive colour signals
- H04N1/6022—Generating a fourth subtractive colour signal, e.g. under colour removal, black masking
- H04N1/6025—Generating a fourth subtractive colour signal, e.g. under colour removal, black masking using look-up tables
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Facsimile Image Signal Circuits (AREA)
Abstract
This invention is concerned with a colour scanner for the graphic arts of the kind in which three uncorrected colour-component analogue signals from the scanner are converted into digital form (20) and are applied to the inputs of a three-dimensional look-up table (24) or read-only memory in which are stored corresponding colour-corrected signal values for the three colours and, if desired, for black. In this invention, individual one- dimensional colour-component look- up tables (22) are interposed between the analogue-digital converters (20) and the three-dimensional look-up table (24) to provide signals representative of print density. The functions performed by the one- dimensional tables may include logarithmic conversion of the input signals, for example. Preferably, further individual one-dimensional look-up tables (28) are inserted between the outputs of the three- dimensional table (24) and a digital- analogue converter (30) preceding an output scanner (34, 36). <IMAGE>
Description
SPECIFICATION
Image-reproduction apparatus
In a colour scanner for the graphic arts some form of adjustable computer is required to convert signals derived from the scanner photomultipliers or photocells into signals which, when applied to the output means of the scanner, will give rise to colour separations or plates which will result in a printed image which is an acceptable reproduction of the original subject. To this end the computer must modify the signals in a manner which takes into account the characteristics of the input and output means of the scanner, the tone or gradation curve appropriate to the particular subject to be scanned, the absorbtions and printing characteristics of the ink, end the editorial modifications to the original subject which may on occasion be required.
The corrections required are however, complicated functions and are not all independent of one another; instead they interact and this makes it difficult to provide for an operator to make adjustments as required for a particular subject or for editorial reasons. Also, the more complicated the functions provided in the correction circuits, the less stable are these circuits.
In recent years, the modified analogue signals, have been converted into digital form in order to permit storage of these signals without losing the image quality in the final reproduction. The signals are extracted from store as required to expose or otherwise treat an output surface. Such storage permits, for example, enlarging by the method described in our patent no. 1,166,091. Of course, when signals are converted to digital form it is necessary to provide a large number of digital or "quantising" levels, because if the steps between levels are too great the transitions between two adjacent quantitising levels will be visible on a finished picture as undesirable contours. The number of levels cannot be increased indefinetly for reasons of storage capacity. The number required can be somewhat reduced by superimposing noise upon the signals.
Because of the difficulty of setting up and maintaining the analogue corrections referred to above and of providing adjustment that an average operator can manage, we suggested in our British patent no. 1,369,702 that the correction should be carried out by means of a digitally operating look-up table; a store was provided with a matrix of colour and tone corrected output values responding to a matrix of colour-component input signal combinations, each representing a point in colour space; these values were loaded in advance of the imagereproducing operation and took into account the modifications required by an operator for the particular work in hand; image-representing signals derived from photomultipliers in the analysing head as it scanned the image to be reproduced were then converted to digital form and were applied to the "look-up table" constituted by the above-mentioned store to
derive the required corrected values at the store
output. For the preliminary loading of the store
with the matrix of output values, parameter values
were set up in accordance with the system
characteristics and the characteristics of the
original to be reproduced. These values were entered into a digital computer programmed to provide the required output-input relationship and, for example, to derive a black printer signal and
remove "undercolour" from the colourcomponent signals.
The use of a digital "look-up" table of this kind gave the advantage of stabiiity in the correction system and overcame the interaction problems. It also facilitated the setting up of the image reproducing apparatus to reproduce a particular image.
However, because all changes of gradation must be performed within a single table, a lack of resolution is experienced in the picture data.
In this specification, the term "uncorrected colour separation signal" is intended to mean a colour separation signal which has not been substantially modified as a function of at least one another colour separation signal to take into account the characteristics of the printing inks and the term "corrected colour separation signal" is intended to mean a colour separation signal which has been so modified.
In a method according to the present invention for the production of colour-separated and colourcorrected images from a coloured original, the original is electro-optically scanned to produce uncorrected colour separation signals which are then converted into digital form; thereafter, each uncorrected colour separation signal is applied to a separate first signal-varying means including an individual digitally stored first look-up table, these first signal-varying means providing signals which have been modified substantially independently of one another; thereafter the modified uncorrected colour separation signals are applied to a further signai-varying means including a digitally stored look-up table to obtain corrected colour separation signals, each of which is a function of two or more of the modified uncorrected colour separation signals; from the corrected signals there are derived output signals for application to one or more output devices by means of which each colour corrected colour separation image is recorded on a recording medium.
In the preferred form of apparatus embodying the invention, each corrected colour separation signal obtained from the further signal-varying means is applied to an output signal-varying means including an individual digitally stored look-up table which further modifies the corrected colour separation signal applied thereto, the further modified signal being used to control the output device.
Each signal-varying means may be constituted by a look-up table operating in an absolute mode or by an incremental look-up table and an adder..
It is an important subsidiary feature of the invention that a larger number of bits is used for the signal immediately following analogue-digital conversion and a smaller number at the output of the first look-up tables. Likewise where the above-mentioned output look-up tables are used a smaller number of bits is used at the input to these final look-up tables and a larger number at the output.
Thus, the first look-up tables may provide a linear-to-logarithmic transformation, converting the linear representation of transmittance or reflectance of the original to a density representation quantised in approximately uniform subjective steps, the density being the desired print density of the reproduction formed by overprinting all the colour corrected colour separation images, as measured through an appropriate colour filter. In practice it is a transformation to an approximately logarithmic form, the curve used providing a better representation of subjectively equal steps of relative luminosity than a true logarithmic curve would provide. An example of such a curve is given by A. J. Johnson, PIRA Report No. PR 143, "A Study of Preferred Tone Reproduction
Characteristics for Colour Reproduction" (Fig. 1 7, Quadrant 1).References in this specification to logarithmic forms should be taken to include such approximate logarithmic forms. A correction may also be incorporated to balance the tracking of the three photomultipliers. The output look-up tables, which are in general different for each channel, may convert the corrected colour separaion signals to print density signals such that when the signals are used to control the output device the desired ink density will ultimately be printed.
The invention also consists in apparatus for carrying out the method defined above.
If desired, some analogue signal processing may be carried out in each colour separation channel, before analogue-to-digital conversion takes place:
Thus, for example the logarithmic conversion or shadow compression may be introduced in this way. Also, some linear or non-!inear crosscoupling between channels may take place before analogue-to-digital conversion, to provide compensation for defects in the separating filters.
In order that the invention may be better understood, an example of apparatus embodying the invention will now be described with reference to the accompanying drawing.
In the drawing, the picture signals (yellow, magenta, cyan) from the photomultipliers are applied to analogue-to-digital conversion circuits 20 and the resulting digital signals in 12-bit form are applied to first look-up tables 22 which provide the linear-to-logarithmic transformation.
The resulting digital signals in the logarithmic range comprises 8 bits. These logarithmic signals are applied to a look-up table 24 representing 3dimensional colour space and also to an interpolator 26 connected to the table 24 and carrying out a function similar to that described in our British Patent No. 1369702. The table 24 and the interpolator 26 correct for defects in printing ink colours, generate the black separation signals, and carry our under-colour removal. It should be understood that the table 24 is really four independent 3-dimensional look-up tables, since at each input address four separate values for the four output colours are found. The colour separation signals are derived from the table 24 and interpolator 26 one colour at a time, under the control of a colour selector control unit 27.A train of 8-bit control signals representing' the selected colour component is applied through a selector switching circuit to the appropriate one of four output look-up tables 28. Thus, assuming that the corrected yellow signal is provided at the ouput of the interpolator 26, this signal will be applied to the look-up table 28Y'.
Each table 28 is of one-dimensional form and converts transparency density to print density. The output of table 28 is in 12-bit form, allowing for a gain change of sixteen without loss of resolution.
The 12-bit signal from the selected table 28 is then applied through a selector switch 31 to a digital-to-analogue converter 30 and thence through modulator amplifier 32 to control a light source in exposing head 34 which exposes a lightsensitive surface on the cylinder 36.
Generally speaking, the first look-up tables will be reloaded to suit each individual coloured original. The 3-dimensional table 24 primarily corrects for ink characteristics and needs to be changed only when an individual coloured original requires some special alteration. Each output lookup table corrects for the characteristics of the output device, recording medium and press, and needs to be modified only when one of these is changed.
The apparatus described above permits changes in range and colour bias between one original and the next to be dealt with without recomputing the 3-dimensional look-up table. The 3-dimensional table 24 has 4096 entries, whereas each 1 < 'imensional table 22 has only 256 distinct entries corresponding to the 8-bit output, these being appropriately replicated to fill the 4096 entries of the table. Thus the process of recomputing input look-up tables is 4 times faster than that of re-computing the main 3-dimensional table.'ln addition, the configuration described above enables an input resolution from the analogue system of 12 bits without expanding the 3-dimensional look-up table to an unreasonable size. This makes it practical to simplify the analogue signal processing by omitting "logging" stages, (stages convertingthe signal to logarithmic form), whicha're' generally a source of trouble in achieving stability and accuracy. A somewhat similar argument applies in respect of advantages obtained by the use of 8 bit to 12 bit output look-up tables.
In the above description, it has been assumed that the black printer is generated in the same manner as the colour separation printers, having its own output from the look-up table 24 and interpolator 26 and its own final look-up table 28.
In an alternative and more econimical way of generating the black printer, hard-wired logic is used to select the smallest of the three signals emerging from the first look-up tables 22 and the smallest signal is transferred directly to a black output look-up table (one-dimensional), the output of which provides the signal for exposing the black printer. This has the advantage that the look-up table 24 and interpolator 26 need only generate three signals instead of four.
A disclosure of the general arrangement of the analysing and recording scanners and of the circuits for controlling the operation of the scanners is given in British Patent No. 1,166,091.
Claims (11)
1. a method for the production of colourseparated and colour-corrected images from a coloured original, comprising the steps of:
electro-optically scanning the original to produce uncorrected colour separation signals which are then converted into digital form;
applying each of the said uncorrected colour separation signals to a separate first signal varying means including an individual digitally stored first look-up table, these first signal-varying means providing signals which have been modified substantially independently of one another;
thereafter applying the modified uncorrected colour separation signals to a further signalvarying means including a digitally stored look-up table to obtain corrected colour separation signals, each of which is a function of two or more of the modified uncorrected colour separation signals; and
from the corrected signals, deriving output signals for application to one or more output devices by means of which each colour corrected colour separation image is recorded on a recording medium.
2. A method in accordance with claim 1, comprising applying each corrected colour separation signal obtained from the colourcorrecting signal-varying means to an output signal-varying means including an individual digitally stored look-up table which further modifies the corrected colour separation signal applied thereto, the further modified signal being used to control the output device.
Apparatus for the production of colourseparated and colour-corrected images from a coloured original, comprising;
an electro-optical scanner for producing uncorrected colour separation signals corresponding to successively scanned elements of the original;
an analogue-to-digital converter for converting the said signals into digital form;
a separate first signal-varying means, including an individually digitially stored first look-up table, connected to receive each of the said uncorrected colour separation signals, these first signal-varying means providing signals which have been modified substantially independently of one another;;
colour-correcting signal-varying means connected to receive the modified uncorrected colour separation signals, the colour-correcting signal-varying means including a digitally stored look-up table for providing colour-corrected colour separation signals, each of which is a function or two or more of the modified uncorrected colour separation signals; and
means for deriving from the colour-corrected signals, output signals for application to one or more output devices by means of which each colour-corrected colour-separation image is recorded on a recording medium.
4. Apparatus in accordance with claim 3, further comprising a separate output signalvarying means for each corrected colour separation signal obtained from the colourcorrecting signal-varying means, each output signal-varying means including an individually digitally stored look-up table which further modifies the corrected colour separation signal applied thereto the further modified signal being used to control the output device.
5. Apparatus in accordance with claim 3 or 4, in which the look-up tables operate in an absolute mode.
6. Apparatus in accordance with claim 3 or 4, in which the look-up tables operate in an incremental manner.
7. Apparatus in accordance with claim 3 in which a number of bits used for the signal immediately following analogue-digital conversion is greater than the number of bits used for the signal at the output of the first look-up tables.
8. Apparatus in accordance with claim 4, in which the number of bits used at the input to the output look-up tables is smaller than the number of bits obtained at the output.
9. Apparatus in accordance with any one of claims 3 to 8, in which the first look-up tables provide a linear-to-logarithmic transformation, converting the linear representation of transmittance or reflectance of the original to a density representation.
10. A method for the production of colourseparated and colour-corrected images from a coloured original substantially as herein described.
11. Apparatus for the production of colourseparated and colour-corrected images from a coloured original substantially as herein described, with reference to the accompanying drawing.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8016963A GB2050751B (en) | 1979-05-30 | 1980-05-22 | Image-reproduction apparatus |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB7918806 | 1979-05-30 | ||
GB8016963A GB2050751B (en) | 1979-05-30 | 1980-05-22 | Image-reproduction apparatus |
Publications (2)
Publication Number | Publication Date |
---|---|
GB2050751A true GB2050751A (en) | 1981-01-07 |
GB2050751B GB2050751B (en) | 1983-06-29 |
Family
ID=26271700
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB8016963A Expired GB2050751B (en) | 1979-05-30 | 1980-05-22 | Image-reproduction apparatus |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2050751B (en) |
Cited By (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3220298A1 (en) * | 1981-06-01 | 1982-12-16 | Canon K.K., Tokyo | COLOR IMAGE READER |
EP0084228A2 (en) * | 1981-12-07 | 1983-07-27 | Xerox Corporation | Digital color modification |
US4500919A (en) * | 1982-05-04 | 1985-02-19 | Massachusetts Institute Of Technology | Color reproduction system |
WO1990015404A1 (en) * | 1989-05-30 | 1990-12-13 | Eastman Kodak Company | Apparatus for interfacing video frame store with color display device |
EP0410719A2 (en) * | 1989-07-25 | 1991-01-30 | Seiko Instruments Inc. | Colour correction system and method |
WO1991019376A1 (en) * | 1990-06-01 | 1991-12-12 | Cymbolic Sciences International Ltd. | Real time transformation between colour spaces |
EP0487304A2 (en) * | 1990-11-20 | 1992-05-27 | Canon Kabushiki Kaisha | Color image processing |
EP0220903B1 (en) * | 1985-10-22 | 1993-09-29 | Konica Corporation | Image-processing apparatus |
EP0615379A1 (en) * | 1993-03-08 | 1994-09-14 | Canon Kabushiki Kaisha | Colour conversion apparatus |
EP0695080A3 (en) * | 1994-07-29 | 1996-05-29 | Canon Kk | Image processing apparatus and method thereof |
AU678798B2 (en) * | 1993-03-08 | 1997-06-12 | Canon Kabushiki Kaisha | Colour conversion apparatus |
EP1096788A2 (en) * | 1999-10-14 | 2001-05-02 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
EP1365575A1 (en) * | 2002-05-23 | 2003-11-26 | GRETAG IMAGING Trading AG | Method and apparatus for improving image contrast |
US6766049B2 (en) | 1993-08-27 | 2004-07-20 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and method |
US6829062B2 (en) | 1998-04-20 | 2004-12-07 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
US6865292B1 (en) | 1999-01-27 | 2005-03-08 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
-
1980
- 1980-05-22 GB GB8016963A patent/GB2050751B/en not_active Expired
Cited By (30)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3220298A1 (en) * | 1981-06-01 | 1982-12-16 | Canon K.K., Tokyo | COLOR IMAGE READER |
EP0084228A2 (en) * | 1981-12-07 | 1983-07-27 | Xerox Corporation | Digital color modification |
EP0084228A3 (en) * | 1981-12-07 | 1985-05-02 | Xerox Corporation | Digital color modification |
US4500919A (en) * | 1982-05-04 | 1985-02-19 | Massachusetts Institute Of Technology | Color reproduction system |
EP0220903B1 (en) * | 1985-10-22 | 1993-09-29 | Konica Corporation | Image-processing apparatus |
WO1990015404A1 (en) * | 1989-05-30 | 1990-12-13 | Eastman Kodak Company | Apparatus for interfacing video frame store with color display device |
EP0429583A1 (en) * | 1989-05-30 | 1991-06-05 | Eastman Kodak Company | Apparatus for interfacing video frame store with color display device |
EP0410719A2 (en) * | 1989-07-25 | 1991-01-30 | Seiko Instruments Inc. | Colour correction system and method |
EP0410719A3 (en) * | 1989-07-25 | 1992-01-22 | Seiko Instruments Inc. | Colour correction system and method |
US5479272A (en) * | 1989-07-25 | 1995-12-26 | Seiko Instruments Inc. | Color gradation correction system of combination of looking-up table and interpolation and method thereof |
WO1991019376A1 (en) * | 1990-06-01 | 1991-12-12 | Cymbolic Sciences International Ltd. | Real time transformation between colour spaces |
US5564006A (en) * | 1990-06-01 | 1996-10-08 | Cymbolic Sciences International, Inc. | Real time transformation between color spaces |
US5315415A (en) * | 1990-11-20 | 1994-05-24 | Canon Kabushiki Kaisha | Color image processing apparatus |
EP0487304A2 (en) * | 1990-11-20 | 1992-05-27 | Canon Kabushiki Kaisha | Color image processing |
EP0487304A3 (en) * | 1990-11-20 | 1993-01-13 | Canon Kabushiki Kaisha | Color image processing |
EP0615379A1 (en) * | 1993-03-08 | 1994-09-14 | Canon Kabushiki Kaisha | Colour conversion apparatus |
AU678798B2 (en) * | 1993-03-08 | 1997-06-12 | Canon Kabushiki Kaisha | Colour conversion apparatus |
US5809181A (en) * | 1993-03-08 | 1998-09-15 | Canon Information Systems Research Australia Pty. Limited | Color conversion apparatus |
US6766049B2 (en) | 1993-08-27 | 2004-07-20 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and method |
EP0695080A3 (en) * | 1994-07-29 | 1996-05-29 | Canon Kk | Image processing apparatus and method thereof |
US5937087A (en) * | 1994-07-29 | 1999-08-10 | Canon Kabushiki Kaisha | Image processing apparatus and method thereof |
US7146044B2 (en) | 1994-08-18 | 2006-12-05 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and method |
USRE41199E1 (en) | 1994-08-18 | 2010-04-06 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and method |
US6829062B2 (en) | 1998-04-20 | 2004-12-07 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
US6904167B2 (en) | 1998-07-10 | 2005-06-07 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and method |
US6865292B1 (en) | 1999-01-27 | 2005-03-08 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
EP1096788A2 (en) * | 1999-10-14 | 2001-05-02 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
EP1096788A3 (en) * | 1999-10-14 | 2003-11-05 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
US6839150B1 (en) | 1999-10-14 | 2005-01-04 | Mitsubishi Denki Kabushiki Kaisha | Color conversion device and color conversion method |
EP1365575A1 (en) * | 2002-05-23 | 2003-11-26 | GRETAG IMAGING Trading AG | Method and apparatus for improving image contrast |
Also Published As
Publication number | Publication date |
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GB2050751B (en) | 1983-06-29 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19950522 |