DE19752479A1 - Correction system for light uniformity for photographic copy printing - Google Patents

Abstract

The system (10) contains an optical exposure system for printing an image on a photosensitive medium. It contains an exposure light source (36) and an imaging active matrix LCD (24) to generate an image, through which passes the exposure light for printing the image on the photosensitive medium (26). Between the imaging display and light source is incorporated an active matrix correction LCD (50) for equalising uniformity discrepancies in the optical exposure system. A first input polariser acts on the light impinging on the imaging display, while an output polariser acts on the light transmitted by the imaging display.

Description

The invention relates to a method for correcting light unevenness of an image forming system which has a liquid crystal display with a active matrix used to print an image onto a photosensitive medium thinning by pushing the light for exposure through the image display as well a device with an optical exposure system for printing an image on a photosensitive medium that is used to copy a digital data generated image uses a liquid crystal display (LCD, Liquid Crystal Display).

For example, US-A-4,935,820 and US-A-5,050,001 disclose a single one Liquid crystal display for producing a color image on a photographic To use material. The liquid crystal display uses digital information from scanning a photographic film negative or from another source. When implementing one used for copying on photographic material The problem is that the light strength across the liquid crystal display is not uniform. The Fluctuations can also be time and temperature dependent. US-A-4,935,820 describes the correction of the light intensity by setting individual pixels of the rivers sig crystal display. The disadvantage of doing this is that the dynamic range of the digital data of the liquid crystal display is reduced becomes. Another problem is that because of the limited dynamics area of a single liquid crystal display, prints of lower quality be generated.  

The invention provides a method and an apparatus for digital copying photographic media ready, that or the unevenness of the for the Belich used light can be corrected. This is accomplished by a second Active matrix liquid crystal display in series with the active matrix liquid crystal display Education display provided and a calibration procedure is used to Cor to determine the correction values used to correct the unevenness will.

According to an embodiment of the invention, there is provided an apparatus for copying an image onto a photosensitive medium. The device comprises an optical exposure system with the following components:

• (a) a light source for generating light for exposure;
• (b) an active matrix liquid crystal image display for forming an image, through which the light for exposure to copy the image onto a light sensitive medium occurs; and
• (c) an active matrix flux arranged between the image display and the light source sig crystal correction display for correcting an optical exposure unevenness.

According to another embodiment of the invention, there is provided a method for correcting the light unevenness of an imaging system that uses an active matrix liquid crystal imaging display to expose an image to a photosensitive medium by passing the light for exposure through the imaging display, wherein the process comprises the following steps:
Measuring the non-uniformity of light for exposure;
Adjust the intensity of light for exposure at individual locations before the light passes through the image display to compensate for the measured unevenness.

According to another embodiment of the invention, there is provided a method of correcting the light unevenness of an optical system for exposing a photosensitive medium, the optical system comprising an active matrix liquid crystal imaging display used to expose an image to the photosensitive medium from an exposure light that enters the medium through the image display, the method comprising the following steps:

• (a) Determine the unevenness of the light for the exposure after the Light has entered the image display; and
• (b) Adjust the intensity of the light for the exposure, which is shown by the fig display occurs by performing a second active matrix liquid crystal correction display in response to the previously determined unevenness distribution is used.

According to another embodiment of the invention, there is provided a method for correcting the light unevenness of an imaging system that uses an active matrix liquid crystal imaging display to expose an image to a photosensitive medium by passing the light for exposure through the imaging display and an active matrix liquid crystal correction display for correcting the exposure light intensity, the method comprising the following steps:

• (a) Measuring the unevenness of what is passing through the image display Light to obtain a first distribution value;
• (b) comparing the first distribution value with a predetermined distribution value;
• (c) setting correction distribution values to operate the correction display;
• (d) applying the correction distribution values to the correction display; and  
• (e) repeating steps (a) through (c) until the correction distribution values are within predetermined limits.

The invention is described below with reference to an off in the drawing management example explained in more detail.

Show it

Fig. 1 is a schematic representation of the printer device according to the invention;

FIG. 2 is an exploded perspective view of the imaging section of the device from FIG. 1, showing in particular the two active matrix liquid crystal displays and a filter wheel arranged therebetween;

Fig. 3 is a plan view of the filter wheel of Fig. 1 and 2;

Figure 4 is a schematic representation of the front of the CCD sensor used for calibrating the light irregularity in the printer. and

Fig. 5 is a graphical representation of three curves, one curve representing the uniformity of the lighting system, a second curve the setting to be used for the previous curve and a third curve the light uniformity after the correction.

Referring to Fig. 1, an inventive photographic high-speed printer 10 is shown in schematic form. The high-speed photographic printer 10 in particular comprises a digital copying system 12 . The high speed photographic printer 10 includes a supply spool 16 which contains a plurality of developed photographic film negative strips, each strip representing a single customer order. The individual strips are each glued to one another in such a way that a long endless web 17 is formed. A scanner 14 scans the endless web 17 which is movable past the scanner 14 . In the illustrated embodiment shown, the scanner 14 comprises a CCD (Charge Coupled Device) arrangement for acquiring digital information representing the images present on the continuous web 17 . The resolution of scanner 14 is preferably equal to or higher than the resolution in the finished image. The digital information determined by the scanner 14 is passed on to a central processing unit 22 (a computer). A take-up reel 18 winds up the endless web 17 which is unwound from the supply reel 16 . Suitable means (not shown) are provided for winding the continuous web 17 from the supply reel 16 onto the take-up reel 18 .

The digital copying system 12 includes an active matrix liquid crystal display (AMLCD) 24 to provide images that can be exposed on a photosensitive medium. In the particular embodiment shown, the light-sensitive medium is a photo paper 26 unwound from a spool 28 . Means known in the prior art are provided for transporting the photo paper 26 to the copying stage 29 . The active matrix liquid crystal imaging display 24 comprises a monochrome display, preferably with a minimum number of 800 × 600 pixels. A suitable active matrix liquid crystal imaging display is available from Epson Corporation under part number P13SM015. In order to provide a high quality image, the number and arrangement of the pixels of the active matrix liquid crystal image display 24 should correspond to the number and arrangement of the pixels in the CCD sensor 14 . Preferably this relationship is 1: 1 or greater. The digital copying system 12 also includes a light source 36 for providing the light required for the exposure and an infrared cut filter 38 for eliminating unwanted portions of the light spectrum of the kind that essentially only visible light passes through. A color filter wheel 40 is disposed in front of the active matrix liquid crystal image display 24 and is used to color the image on the photo paper 26 . The filter wheel 40 (see FIG. 3) in particular comprises the filter sections 42 , 44 , 46 , filter section 42 being a blue filter, filter section 44 a green filter and filter section 46 a red filter. By rotating the filter wheel 40 about axis 48 , the desired color filter section can be positioned between the light source 36 and the image display 24 in such a way that a color image is formed on the photo paper. The filter wheel 40 is provided with an opaque portion 47 to keep light emitted from the light source 36 away, so that the photo paper 26 is not exposed during the exposure-free time of the digital copying process. A lens 49 is provided for focusing the image generated by the active matrix liquid crystal image display 24 on the photo paper 26 . The central processing unit 22 , which receives the digital information determined by the scanner 14 , is also used to control the various components of the device according to known techniques and also provides the corresponding digital data for generating the images on the active matrix liquid crystal. Image display 24 ready.

In order to produce a single color image on the photo paper 26 , the filter wheel 40 must be rotated and the image must remain on the active matrix liquid crystal image display 24 for an appropriate time, so that each individual filter section for the appropriate amount of time is exposed. It has been found that when using the digital copying system, full-color images can be exposed on the photographic paper in about 0.25 seconds.

An active matrix liquid crystal correction display 50 is provided which is used to provide correction factors to compensate for the unevenness of the exposure system and the imaging system of the digital printer.

Referring to Fig. 2 of the imaging section of the digital copying system 12 is shown in greater detail, which generates the images on photo paper 26. As is known to a person skilled in the art, it is possible with an active matrix liquid crystal display to access each individual pixel in such a way that each individual pixel can be activated in a suitable manner. In a typical active matrix liquid crystal display, a first polarizer 52 is provided for polarizing the incident light in a first axis. Each individual pixel can be controlled by a corresponding voltage, which in turn can control the polarization of each individual pixel. A second polarizer 56 is provided for polarizing the light emerging from the active matrix liquid crystal display. The active matrix liquid crystal display can be set up in such a way that it enables transparent transmission of the light, whereby less light passes through the active matrix liquid crystal display by controlling the voltage. However, it can also be designed as a black display, with more light passing through the active matrix liquid crystal display by controlling the voltage. According to the prior art, the first polarizer 52 is arranged at an angle of 90 degrees to the second polarizer 56 . By adjusting the voltage of each pixel of the active matrix liquid crystal display, the corresponding amount of light can pass through. Since two active matrix liquid crystal displays 24 and 50 are provided in the same optical beam path, one of the polarizers normally present can be eliminated. In the present case, the active matrix liquid crystal image display 24 therefore comprises only a single polarizer 58 . The active matrix liquid crystal imaging display 24 is positioned such that the polarizer 58 is positioned at an angle of 90 degrees to the polarizer 56 . By positioning the active matrix liquid crystal image display 24 such that the polarizer is at 90 degrees to the polarizer 56 of the active matrix liquid crystal correction display 50 , one normally of the active matrix liquid crystal image display 24 assigned second polarizer are omitted. This increases the amount of light available for passage compared to the amount of light that would normally be available if two normal active matrix liquid crystal displays were arranged one behind the other. However, if the amount of light available is not important, the active matrix liquid crystal image display 24 could also be provided with two polarizers. In the illustrated embodiments, the active matrix liquid crystal correction display 50 has two polarizers, while the active matrix liquid crystal imaging display 24 is equipped with one polarizer. This ratio could be reversed so that the active matrix liquid crystal correction display 50 has one and the active matrix liquid crystal image display 24 has two polarizers.

Various light non-uniformities can occur in the active matrix liquid crystal display copying system according to the invention. For example, the active matrix liquid crystal image display 24 and the active matrix liquid crystal correction display 50 have natural non-uniformities by design. In addition, temperature changes to which an active matrix liquid crystal display is subject from commissioning to stable operating status can lead to irregularities. Individual pixels of an active matrix liquid crystal display can also change uniformly or unevenly over time. Depending on the light source or lens used in the system, further irregularities may occur. These non-uniformities can be compensated for by adjusting the signal sent to the active matrix liquid crystal image display 24 . However, the available dynamic range suffers from this and the image quality is considerably reduced.

There are several ways to determine the non-uniformity information required to drive the active matrix liquid crystal correction display 50 . For example, it is possible to use the active matrix liquid crystal image display 24 to make a photographic copy of a known image (flat field) on the light-sensitive material. Then the density of the developed image could be measured with a densitometer. By measuring the image density at different locations on the copy, a map of the light unevenness of the imaging system can be generated. This information can be passed to the central processing unit 22 , where a compensation algorithm calculates the data for setting the intensity levels of the active matrix liquid crystal correction display 50 . Unfortunately, this approach requires a lot of processing and cannot be completed very quickly. The photographic copy must first be developed and analyzed. Subsequently, the map of the irregularities must be fed back into the central processing unit 22 in order to correct the active matrix liquid crystal correction display 50 and to activate it accordingly.

Referring to Fig. 1, a system is shown, in which information about irregularities quickly and easily by using a linear CCID Anord can be determined voltage 60 and a rotating mirror 62nd The rotating mirror 62 is arranged in such a way that it can be pivoted between a normal non-calibration position, as shown by the solid lines, and a calibration position, as shown by the dashed lines. The rotating mirror 62 is rotatably arranged on the device 10 before such that the exposure light passing through the imaging system is scanned in order to obtain an intensity profile of the entire exposure light. The uniformity of the lighting system is determined using a calibration method, including the active matrix liquid crystal image display 24 and the active matrix liquid crystal correction display 50 . At the beginning of the calibration process, the active matrix liquid crystal correction display 50 is first brought into a first state in which light can pass through the active matrix liquid crystal correction display 50 without restriction (ie in a transmitted light mode). The active matrix liquid crystal image display 24 is in the dark mode. The rotating mirror 62 is moved from the non-calibration position to the calibration position and enables the CCD arrangement 60 to scan the light used for copying, in order to determine the required intensity information for the exposure system. This information is used by the central processing unit 22 to provide a first pixel matrix for offset corrections. Then the active matrix liquid crystal image display 24 is switched to full transmitted light mode. The rotating mirror 62 is again moved into the calibration position so that the CCD arrangement 60 can scan the exposure light in order to determine a second pixel correction matrix. The central processing unit 22 determines a correction pixel matrix on the basis of the information obtained for each of the two light states of the active matrix liquid crystal image display 24 . The exposure intensity values are thus determined for a large number of very small, individual, discrete areas by measuring individual pixels of the CCD arrangement which are representative of the entire exposure area.

FIG. 5 shows a curve A which represents the optical response of the system based on two pixel matrices. As shown in FIG. 5, curve B in particular represents the desired response behavior. A suitable countermeasure curve C is thus determined for each pixel of the matrix, so that the response behavior ultimately achieved would approach curve B. Once this information has been calculated, it is used to drive the active matrix liquid crystal correction display 50 . The active matrix liquid crystal correction display 50 is then subjected to a first correction setting. The previously described calibration procedure is then repeated to generate a new pixel correction matrix. The result is compared to the desired curve. If further settings are required, the settings are calculated by the central processing unit and used to program the active matrix liquid crystal correction display 50 . This process is repeated until the values for the pixel correction matrix lie within the desired tolerance limits. If desired, a medium setting for the active matrix liquid crystal image display 24 can be achieved to verify the operating characteristics of the active matrix liquid crystal image display 24 .

Referring to FIG. 4 is an end view of the CCD array processing system 60 used to calibrate the BL LEVEL is shown. The mirror 62 is movable with either a spring (not shown) or a stepper motor at a substantially constant speed such that light is projected onto the CCD assembly 60 . This image data collected by the CCD array 60 is used to generate the pixel correction matrix previously discussed. In the preferred embodiment, linear CCD array 60 is used to reduce costs and avoid the costs of using a more expensive area CCD array. However, the invention is not restricted to a linear CCD arrangement. The rotating mirror 62 only needs to be brought into a second stationary position in order to correctly project the exposure light onto the surface CCD arrangement in such a way that the previously discussed pixel matrix information can be determined.

In the preferred embodiment of the invention, a second active matrix Liquid crystal display used to make correction measurements on exposure light remote places. Other means can also be used for example, without being restrictive, a filter mask that is blackened in appropriate discrete areas. The making of one However, the mask would cause additional time and costs therefore not currently preferred.

The invention provides a method and an apparatus for digital copying system ready to correct the unevenness of light for exposure.

Reference list

10th

high speed photographic printer

12th

digital copying system

14

Scanner

16

Storage spool for film negatives

17th

Endless web of film negatives

18th

Take-up spool

22

central processing unit

24th

Active matrix liquid crystal image display

26

Photo paper

28

Storage spool for photo paper

29

Copy stage

36

Light source

38

Infrared cut filter

40

Color filter wheel

42,

44

,

46

Filter sections

47

opaque section

48

axis

49

lens

50

Active matrix liquid crystal correction display

52,

56

,

58

Polarizer

60

CCD arrangement

62

Rotating mirror

Claims (18)

1. Device ( 10 ) with an optical exposure system for printing an image on a light-sensitive medium, characterized by

• - a light source ( 36 ) for generating light for exposure;
• an active matrix liquid crystal image display ( 24 ) for forming an image through which the light for exposure passes to print the image on a photosensitive medium ( 26 ); and
• - An arranged between the image display ( 24 ) and light source active matrix liquid crystal correction display ( 50 ) for correcting an existing in the optical exposure system unevenness.

2. Device according to claim 1, characterized in that

• - A first input polarizer ( 52 ) for polarizing the incident light in the image display and a second output polarizer ( 56 ) for polarizing the light leaving the image display ( 24 ) is provided;
• - The image display ( 24 ) is arranged in a first orientation;
• - A third input polarizer ( 58 ) for polarizing the correction light ( 50 ) incident light is provided; and
• - The correction display ( 50 ) is arranged in a second orientation so that the third input polarizer is arranged at an angle of 90 ° to the first input polarizer.

3. Device according to claim 1, characterized by a control means ( 22 ) for controlling and setting the correction display. 4. The device according to claim 3, characterized in that the control means comprises a sensor ( 60 ) for measuring the non-uniformity in the optical system and generating measurement information for the control means. 5. The device according to claim 4, characterized in that the control means a calculator for controlling the correction display depending on the Has measurement information. 6. The device according to claim 4, characterized in that the control means comprises a mirror attached to the device ( 62 ) for the movement between a first, non-calibration position and a second, calibration position for scanning the light leaving the image display and the sensor ( 60 ) acting light . 7. The device according to claim 6, characterized in that an engine Mirror with a substantially constant speed between the first and second position rotates. 8. The device according to claim 7, characterized in that the sensor ( 60 ) is a linear CCD array. 9. The device according to claim 6, characterized in that the sensor CCD area array is. 10. The device according to claim 1, characterized in that the imaging display ( 24 ) has a first input polarizer and a second output polarizer and the correction display ( 50 ) has a single third input polarizer, which is arranged at an angle of 90 ° to the first input polarizer . 11. A method for correcting the light unevenness of an image forming system which uses a liquid crystal display with an active matrix to expose an image to a photosensitive medium by penetrating the light for exposure through the image display, characterized by the following steps:
Measuring the non-uniformity of light for exposure; and

• - Depending on the measured unevenness, setting the intensity of the light for the exposure at individual points before the light passes through the image display in order to compensate for the measured unevenness.

12. The method according to claim 11, characterized in that the setting arranged by using a between light source and image display Liquid crystal correction display with active matrix and the control of the Correction is displayed. 13. The method according to claim 12, characterized in that the measurement according to Passing the light through the image display is done. 14. The method according to claim 12, characterized in that the measurement and control is carried out according to the following steps:

• (a) putting the correction indicator in an erased state;
• (b) placing the image display in a first intensity setting;
• (c) measuring the non-uniformity of the light to obtain a first pixel representation of the light for the first setting;
• (d) placing the image display in a second intensity setting different from the first intensity setting;
• (e) measuring the non-uniformity of the light to obtain a second pixel representation of the light for the second setting;
• (f) using the first and second pixel representations to obtain a system response;
• (g) defining a correction matrix for use in calculating correction values for the correction display; and
• (h) Apply the correction values to the correction display.

15. The method according to claim 14, characterized by the following step:

• (i) repeating steps (a) to (h) until the correction values are in a predetermined range.

16. The method according to claim 12, characterized in that the measurement and control is carried out according to the following steps:

• (a) measuring the non-uniformity of the light passing through the image display to obtain a first distribution value;
• (b) comparing the first distribution value with a predetermined distribution value;
• (c) setting correction distribution values to operate the correction display;
• (d) supplying the correction distribution values to the correction display; and
• (e) repeating steps (a) through (c) until the correction distribution values are within predetermined limits.

17. The method according to claim 11, characterized in that the measurement by Create a photographic print and measure an image on the print by means of a densitometer in order to achieve a non-uniformity distribution of light to get the exposure. 18. The method according to claim 11, characterized in that the measurement by A CCD array is exposed to the light for the exposure.