JPH06178109A - Image reader having density correcting function and density correcting method - Google Patents

Abstract

PURPOSE:To obtain the image data of the same density for the same image information regardless of the states of the illuminating system and the image formation optical system and the kinds of transmitted original, etc., in an image reading part. CONSTITUTION:Density correction data (a) regarding the Callier coefficient obtained by a preliminary measurement and density correction data (b) regarding the scattering characteristic of an original, etc., are stored in a density correction data storage part 108, the image signal obtained by reading an original is converted into a density signal in a density conversion part 102 and the density correction data (b) is added to the signal. Next, the corrected density signal is converted into the pigment amount signal according to the pigment amount of sensitive material and the density correction data (a) in an END conversion part 104 and the signal is supplied to a color processing part 106. In the color processing part 106, a desired processing is performed for the pigment amount signal and the signal is supplied to an image output device 110.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus having a density correction function for correcting the reading density according to the reading conditions of an illumination system, an image forming optical system, a transparent original, etc. in an image reading section and a density correction. Regarding the method.

[0002]

2. Description of the Related Art In the field of printing and plate making, for example, an image processing system for electrically processing image information recorded on a read original to make a film original plate for the purpose of streamlining work processes and improving image quality. Is widely used.

In this case, for example, the image processing system scans a document on which image information is recorded, obtains an image signal, and performs desired image processing on the image signal, and the image reading device. And an image output device for producing a film original plate based on an image signal processed by the device. Specifically, in the image reading device, light from the illumination system is applied to a transmissive document on which image information is recorded, and the transmitted light is imaged on a photoelectric conversion element such as a CCD through an imaging optical system. An image signal is obtained and desired image processing is performed on this image signal.

[0004]

By the way, in the image reading apparatus, when the slit width of the illumination system, the lens aperture value of the imaging optical system, the lens position, etc. are changed in response to the light amount adjustment, the magnification change, etc., Even for the same document, the level of the image signal obtained by reading, that is, the density of the image may be different. That is, N of the illumination system
This is because the A and the NA of the imaging optical system change, and accordingly, the amount of light reaching the photoelectric conversion element also changes. Moreover, since the light scattering characteristics differ depending on the type of matting agent applied to the transparent original, the glass plate holding the transparent original, and the like, the image density also changes due to these influences.

The present invention has been made in order to eliminate the above-mentioned inconvenience, and the same image information can be obtained regardless of the state of the illumination system and the image forming optical system in the image reading section, the type of the transparent original, and the like. It is an object of the present invention to provide an image reading apparatus and a density correction method having a density correction function capable of obtaining image signals having the same density.

[0006]

In order to achieve the above-mentioned object, the present invention illuminates a transparent original on which image information is recorded with illumination light and converts the transmitted light into an electric signal for reading. An image reading unit and an illumination system in the image reading unit,
A reading condition setting unit that sets a reading condition relating to an imaging optical system, a transparent original, and the like; a density conversion unit that converts an electric signal obtained by the image reading unit into a density signal according to the reading condition;
A density correction data storage unit that holds density correction data corresponding to the reading condition, and a density correction unit that corrects the density signal using the density correction data are provided.

According to the first aspect of the present invention, an image reading unit is set to a predetermined reading condition by irradiating a transparent original on which image information is recorded with illumination light, converting the transmitted light into an electric signal and reading the electric signal. And the second step of obtaining the carrier coefficient a of the predetermined reading condition with respect to the reference reading condition from the predetermined reading condition, and the reading density x under the predetermined reading condition, It is characterized in that it comprises a third step of obtaining the read density y under the reference read condition as y = ax, which is corrected by using the carrier coefficient a obtained in the step.

Further, according to the present invention, an image reading unit which irradiates a transparent original on which image information is recorded with illumination light, converts the transmitted light into an electric signal and reads the electric signal is set to a predetermined reading condition. And the second step of obtaining the carrier coefficient a of the predetermined reading condition with respect to the reference reading condition and the scattering characteristic b determined by the transparent original from the predetermined reading condition, and the predetermined reading condition. The reading density x under the reading condition is corrected using the carrier coefficient a and the scattering characteristic b found in the second process, and the reading density y under the reading condition as a reference is found as y = a · x + b. It is characterized by the following three steps.

[0009]

In the image reading apparatus having the density correction function and the density correction method of the present invention, the image reading unit set to the predetermined reading condition reads the image information of the transparent original and converts the read image information into an electric signal. While converting the signal into a density signal, the density correction data according to the reading conditions relating to the illumination system, the imaging optical system, the type of the transparent original, etc. in the image reading unit is read from the density correction data storage unit, and the density correction data is read. The density signal is corrected in accordance with. In this case, the density correction data includes a carrier coefficient a of the predetermined reading condition with respect to the reference reading condition and a scattering characteristic b determined by the transparent original, and the read density x under the predetermined reading condition. Is corrected to the read density y under the standard read condition with y = a · x + b using the density correction data.
By performing the correction in this way, it is possible to obtain a density signal that does not depend on the reading conditions.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image reading apparatus having a density correction function and a density correction method according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows a schematic structure of an image reading apparatus 10 which is an embodiment of the present invention. This image reading device 10
Conveying means 14 for conveying the document cassette 12, an image reading section 11 for reading image information recorded on a film F which is a transparent document held in the document cassette 12, and desired image processing for the image information. Image processing circuit 1
6 and 6. The document cassette 12 is a film F.
It is sandwiched by supporting glasses 18a and 18b for maintaining the flat surface.

The image reading section 11 is constructed as shown in FIG. That is, the image reading unit 11 is a Koehler illumination optical system unit (hereinafter, simply referred to as an illumination optical system).
20 and a position adjusting mechanism 22 of the illumination optical system 20. The position adjusting mechanism 22 is disposed on the base plate 24 via the substrate 26, and the illumination optical system 20 is provided.
Are arranged in a casing 28 standing on the substrate 26. In addition, side walls 32a, 32b and 34a, 34b are provided on both sides of the base plate 24 and the substrate 26, respectively.
Is provided. The substrate 26 is provided on the side wall of the casing 28.
The adjustment screw 36a screwed onto the side wall portion 34a of the
The side wall portion 32 b of the base plate 24 is attached to the side wall portion 32 b of the base plate 24.
The adjusting screw 36b that is screwed into the abutment contacts. The position of the illumination optical system 20 with respect to the substrate 26 and the position of the substrate 26 with respect to the base plate 24 are respectively adjusted by these adjusting screws 36a and 36b.

The illumination optical system 20 is provided below the light source 40 at the upper end of the casing 28, a pair of cylindrical lenses 42a and 42b provided below the light source 40, and below the cylindrical lenses 42a and 42b. Field stop 44, a filter 46 and a brightness stop 48 disposed below the field stop 44, and the brightness stop 48.
Of a pair of cylindrical lenses 50 disposed under the
a and 50b. The field stop 44 has one end connected to a drive plate described later, and has a plurality of slits 64a, 6 having different slit widths and lengths depending on the image magnification.
4b.

An opening 52 for passing the illumination light L is defined in the base plate 26 and the base plate 24 on which the casing 28 of the illumination optical system 20 is erected, and the opening 52 is vertically downward. The document cassette 12 is carried in by the carrying means 14. Further, in the vertically downward direction of the document cassette 12, a condenser lens 60 that collects the illumination light L that has passed through the document cassette 12, and a photoelectric conversion unit 61 that receives the illumination light L and converts it into an electric signal. And are provided. In this case, the photoelectric conversion means 61 includes prisms 62a to 62c for splitting the illumination light L into R, G, and B optical signals, and a CCD line sensor 63 connected to each prism 62a to 62c.
a to 63c.

The illumination optical system 20 forms the image from the light source 40 at the front focal point of the cylindrical lenses 50a and 50b, and the cylindrical lenses 42a and 42b.
Cylindrical lens 50 of field stop 44 close to
The film F of the original cassette 12 is arranged on the image plane defined by a and 50b. In this case, since the images formed by the cylindrical lenses 50a and 50b of the light source 40 can be set to infinity, it is possible to obtain the effect of preventing uneven illumination. Further, by placing the field stop 44 on the surface close to the cylindrical lenses 42a and 42b, the field stop 4
4 has an advantage that the contour is clear. On the other hand, in order to prevent the generation of Newton's rings, when one of the supporting glasses 18a and 18b constituting the original cassette 12 is made of Nungrea glass, the illumination optical system 20 forms an image of the light source 40 at infinity. Therefore, even at a high magnification, it is possible to make the irregularities of the Nungrea glass inconspicuous. As described above, by applying the illumination optical system 20 including the Koehler illumination optical system to the original cassette 12 using Nungrea glass, it is possible to obtain a good image without roughness.

Next, the position adjusting mechanism 22 is fixed to the fixed plate 66 on the substrate 26. A field stop 44 is connected to an upper portion of one end of a drive plate 70 disposed below the fixed plate 66, and a slider having a roller portion 72 at an upper end of the other end of the drive plate 70. 74 is fixed. The drive plate 70 is pulled by a wall portion 78 of the fixed plate 66 via a spring 76.

On the other hand, an opening 68 through which the roller portion 72 connected to the slider 74 projects is formed in the plane portion of the fixed plate 66.
Is defined. A pair of bearings 80a and 80b are fixedly provided under the fixed plate 66, and the bearings 80 facing each other are provided.
Two guide shafts 82a and 82b are supported substantially parallel between a and 80b. The guide shafts 82a, 82b are attached to the slider 74 by linear ball bearings 84a, 84.
It is inserted through b.

A slider 7 is provided on the upper surface of the fixed plate 66.
An eccentric cam 86, the outer peripheral surface of which is in sliding contact with the roller portion 72 projecting above 4, is provided via a shaft portion 88, and a gear 90 is axially supported by the shaft portion 88 coaxially with the eccentric cam 86. A bracket 92 is fixedly mounted on the fixed plate 66, and a pulse motor 94 is disposed on the upper surface of the bracket 92. The drive shaft of the pulse motor 94 has the gear 9
A pinion 96 that meshes with 0 is connected.

The image processing circuit 16 is, as shown in FIG.
RG which is an analog signal supplied from the image reading unit 11.
A / D converter 10 for converting a B image signal into a digital signal
0 and logarithmically converting the RGB image signal,
Further, by adding density correction data b described later, Y
Using a density conversion unit 102 for converting to an MC density signal and a dye amount conversion function considering density correction data a described later,
An END (Equivalent Neutral) for converting the YMC density signal into a density signal according to the characteristics of the output photosensitive material.
al Density) conversion unit 104, and picture adjustment, color correction, and
It is basically composed of a color processing unit 106 which performs color processing such as gradation conversion and undercolor removal and performs halftone conversion, and a density correction data storage unit 108 which stores the density correction data a and b. In this case, the density signal processed by the color processing unit 106 is transferred to the image output device 110 and reproduced as an image on a desired photosensitive material. The density correction data a and b stored in the density correction data storage unit 108 are read according to the reading magnification in the illumination optical system 20, the setting state of the field stop 44, the type of the document cassette 12 and the film F, and the like. It is specified by the condition setting unit 112.

The image reading apparatus 10 of this embodiment is basically constructed as described above, and next, the density correction data a and b stored in the density correction data storage unit 108 are set. The method will be described.

First, the setting state of the image reading section 11 shown in FIG. 3 is set as a reference state, and the reference chart 12 shown in FIG. 4A is set.
The image information of 0 is read. This standard chart 12
0 is the recording of three steps of gray densities G1, G2, and G3 on the film. Illumination light L from the light source 40
Is a cylindrical lens 42a, 42b, a field stop 4
4, the filter 46, the aperture stop 48, and the cylindrical lenses 50a and 50b are focused on the reference chart 120 held in the original cassette 12, and the transmitted light is then passed through the condenser lens 60 to the prisms 62a to. 62c
Be led to. The prisms 62a to 62c split the transmitted light of the reference chart 120 into three primary colors of R, G, and B and guide them to the CCD line sensors 63a to 63c. The CCD
The RGB image signals obtained by being converted into electric signals by the line sensors 63a to 63c are converted into digital signals by the A / D converting unit 100, and then the density converting unit 102.
Is converted into a YMC density signal.

Next, the setting state of the image reading section 11 is set under various conditions, and the YMC density signal is obtained in the same manner as the above case. For example, the reading magnification is changed by displacing the positions of the condenser lens 60 and the CCD line sensors 63a to 63c in the arrow direction shown in FIG. Further, by driving the pulse motor 94 corresponding to the reading magnification, the eccentric cam 86 is rotated via the pinion 96 and the gear 90, and the field stop 44 is displaced via the drive plate 70 connected thereto. Then, the slits 64a and 64b are switched. In addition, the YMC density is different for the conditions such as the type of film F, the types of support glasses 18a and 18b of the document cassette 12, and whether the document cassette 12 uses oil between the support glasses 18a and 18b. Try to get a signal.

In this way, YMC obtained corresponding to each gray density G1, G2, G3 of the reference chart 120 is obtained.
Density signals G1 _Y , G1 _M , G1 _C , G2 _Y , G2 _M , G
2 _C , G3 _Y , G3 _M , and G3 _C are the concentration x after changing the conditions.
Is plotted as a relation of the reference time concentration y with respect to FIG.
(See B). The relationship of Y, M, and C to each dye obtained by connecting the plotted points using the least squares method is obtained by comparing the respective density correction data with a _Y , a _M , a _C , b _Y , b _M , and b _C.
Can be expressed by the following linear expression.

_Y = a _Y · x + b _Y (1) y = a _M · x + b _M (2) y = a _C · x + b _C (3) In this case, the field stop 44, the reading magnification, and the brightness stop 48
NA (numerical aperture) associated with the change (fixed in the embodiment of FIG. 3)
The variation of the light amount due to the change of can be expressed by a carrier coefficient (ratio between the parallel light density and the diffused light density). The density correction data a _Y , a _M , and a _{C of the} above equations (1) to (3)
Corresponds to this carrier coefficient. Further, the film F is usually coated with a matting agent on its surface, and the amount of light fluctuates due to the influence of scattering of the illumination light L by this matting agent. Therefore, the density correction data b _Y , b _M , and b _C in the equations (1) to (3) correspond to the scattering characteristics due to the matting agent or the like.

Therefore, using the reference chart 120, the density correction data a _Y , a _M , a _C , b _Y , and b for various reading conditions such as the reading magnification, the diaphragm, and the type of the film F are different.
_M and b _C are obtained, and these are stored in the density correction data storage unit 108.
It is stored in advance in.

Next, the document cassette 12 holding the film F on which desired image information is recorded is loaded into the image reading device 10. The original cassette 12 is read by the conveying unit 14 after being conveyed to the image reading unit 11. In this case, the operator sets various reading conditions such as the type of the original cassette 12 and the film F, the reading magnification, and the like, and the reading condition setting unit 112 sets the density correction data a _Y , a _M corresponding to the reading conditions. a _C , b _Y ,
Select b _M and b _C from the density correction data storage unit 108,
It is supplied to the density conversion unit 102 and the END conversion unit 104.

On the other hand, the image reading section 11 reads the image information of the film F as an RGB image signal, and A / D
The conversion unit 100 supplies this to the density conversion unit 102 as a digital signal. In the density conversion unit 102, the RG
The B image signal is logarithmically converted to obtain Y, M, and C density signals d _Y ,
d _M , d _C, and the density signals d _Y , d _M ,
By adding the density correction data b _Y , b _M , and b _C supplied from the density correction data storage unit 108 to d _C , D _Y = d _Y + b _Y (4) D _M = d _M + b _M (5) D _C = d _C + b _C (6) As a result, YMC density signals D _Y , D _M , and D _C corrected for the scattering characteristics of the film F and the document cassette 12 are created.

Next, the YMC density signals D _Y , D _M , D
_C is an image output device 11 in the END conversion unit 104.
0, the dye amount signal E _Y according to the dye amount of the photosensitive material used,
Converted to E _M and E _C. That is, the END converter 10
4, END conversion matrix [E], which is a dye amount conversion function corresponding to the dye amount of the light-sensitive material, and density correction data a _Y , a _M supplied from the density correction data storage unit 108.
a _C and

[0029]

[Equation 1]

As the dye amount signals E _Y , E _M , and E _C are obtained.

The dye amount signal E obtained as described above
_Y , E _M , and E _C are subjected to desired picture adjustment, color correction, gradation conversion, undercolor removal, and the like in the color processing unit 106, and then are output as halftone signals in the image output device 1.
Transferred to 10. The image output device 110 outputs an image to a desired sensitive material corresponding to the END conversion matrix [E] based on the dye amount signals E _Y , E _M , and E _C.

By correcting the density of the image signal as described above, it is possible to obtain an image having a density not depending on the reading conditions.

In the embodiment described above, the case where the density correction data b _Y , b _M , and b _C corresponding to the scattering characteristics of the original cassette 12 including the film F is corrected by the density converter 102 has been described. Instead of using the equations (1) to (3), y = a _Y · x (8) y = a _M · x (9) y = a _C · x (10), and the density correction data a _Y , The dye amount signals E _Y , E _M , and E _C may be corrected using only a _M and a _C. Further, the density correction data b _Y , b _M , and b _C are the decomposition conditions of the film F. The correction may be performed by changing the set densities of the shadow (SD) part and the highlight (HL) part at the time of setting.

[0034]

As described above, according to the present invention, fluctuations in the reading density due to changes in the reading magnification in the image reading unit, changes in the diaphragm of the illumination system, etc. are corrected, and the density not depending on these reading conditions is corrected. An image signal can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an image processing circuit in an image reading apparatus according to the present invention.

FIG. 2 is a configuration block diagram of an image reading apparatus according to the present invention.

FIG. 3 is a cross-sectional view of the configuration of an image reading unit in the image reading apparatus according to the present invention.

FIG. 4A is an explanatory diagram of a reference chart used in the density correction method according to the present invention, and FIG. 4B is an explanatory diagram of the relationship between the density after the change of the reading conditions and the reference time density.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image reading device 11 ... Image reading unit 12 ... Original cassette 16 ... Image processing circuit 20 ... Illumination optical system 22 ... Position adjustment mechanism 100 ... A / D conversion unit 102 ... Density conversion unit 104 ... END conversion unit 106 ... Color processing Unit 108 ... Density correction data storage unit 110 ... Image output device 112 ... Reading condition setting unit 120 ... Reference chart

Claims (4)

[Claims] 1. An image reading section for irradiating a transparent original on which image information is recorded with illuminating light and converting the transmitted light into an electric signal for reading, and an illumination system and an image forming optical system in the image reading section. A reading condition setting unit for setting a reading condition for a transparent original, a density converting unit for converting an electric signal obtained by the image reading unit into a density signal according to the reading condition, and a density correction corresponding to the reading condition. An image reading apparatus having a density correction function, comprising: a density correction data storage unit that holds data; and a density correction unit that corrects the density signal using the density correction data. 2. The apparatus according to claim 1, wherein the density correction unit uses the density signal as a dye amount of a recording material for recording the image information based on a dye amount conversion function corrected by the density correction data. An image reading apparatus having a density correction function, which comprises a dye amount conversion unit for converting a corresponding dye amount signal. 3. A first step of irradiating a transparent original on which image information is recorded with illumination light, converting the transmitted light into an electric signal and reading the image by a predetermined reading condition. From the predetermined reading condition, a second step of obtaining the carrier coefficient a of the predetermined reading condition with respect to the reference reading condition and the reading density x under the predetermined reading condition were obtained in the second step. A density correction method comprising: a third step of correcting using a carrier coefficient a, and obtaining a read density y under a reference reading condition as y = a · x. 4. A first step of irradiating a transparent document on which image information is recorded with illumination light, converting the transmitted light into an electric signal and reading the image by a predetermined reading condition. From the predetermined reading condition, a second step of obtaining a carrier coefficient a of the predetermined reading condition with respect to a reference reading condition and a scattering characteristic b determined by the transparent original; A third process in which the read density x is corrected using the carrier coefficient a and the scattering characteristic b found in the second process, and the read density y under the standard reading condition is obtained as y = a · x + b. A density correction method comprising: