JPH0370366A - Image reader - Google Patents

Abstract

PURPOSE:To reproduce the intended gradation by binarizing an image, based on a binarization threshold designated by an external device, etc. CONSTITUTION:Density of a document is detected by a density detecting means 12, and from a distribution of density detected by the density detecting means 12, reference density is determined by a reference density determining means 24. Subsequently, based on a gradation characteristic curve in which the reference density determined by the reference density determining means 24 and optimum density of a reproduced image are allowed to correspond to each other, and also, the prescribed maximum density and the maximum density of the reproduced image are allowed to correspond to each other, and moreover, the prescribed minimum density and the minimum density of the reproduced image, an inputted binarization threshold is converted by a converting means 28, and based on the binarization threshold converted by the converting means 28, the image is binarized by a binarizing means 25. In such a way, the intended gradation is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device that binarizes an image based on a binarization threshold specified by an external device or the like.

[Prior Art] A conventional image reading device sets a slice level corresponding to a numerical standard density to a fixed normal density, that is, a binarized density, and outputs it darker (by lowering the slice level). ) or to output thinly (increase the slice level).

[Problems to be Solved by the Invention] However, in the conventional example described above, the normal density of the specified binarized density does not necessarily match the optimum density of the document that is currently being read. When reproducing images, for example, if you want to print out the thin parts of a document, or just the thin parts, you have to scan and print several times, and then decide on the density based on the output results, which is very tedious. Ta.

As a method to solve such problems, the so-called A
E and automatic binarization have been proposed. However, A
The various methods of AE are not universally applicable to various types of images, and it is often the case that images actually obtained by AE are read after changing the density again. In such a case, there was a problem as to how much should be ``slightly darker'' or ``slightly lighter''.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading device that can solve the above-mentioned problems and reproduce intended gradations.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides an image reading device having an input means for inputting a binarization threshold value, which includes a density detection means for detecting the density of a document; , a reference density determining means for determining a reference density from the density distribution detected by the density detecting means; and a reference density determining means for associating the reference density determined by the reference density determining means with the optimum density of the reproduced image, and a predetermined maximum density. Conversion means for converting the binarization threshold value input by the input means based on a gradation characteristic curve in which the density corresponds to the maximum density of the reproduced image, and the predetermined minimum density corresponds to the minimum density of the reproduced image. and a binarization means for binarizing based on the binarization threshold converted by the conversion means.

[Function] In the present invention, the density of the original is detected by the density detection means,
A reference density is determined by a reference density determining means from the distribution of density detected by the density detecting means, and the reference density determined by the reference density determining means is made to correspond to the optimum density of the reproduced image, and a predetermined maximum density and reproduction are performed. Based on a gradation characteristic curve in which the maximum density of the image corresponds to the minimum density of the reproduced image, and the predetermined minimum density corresponds to the minimum density of the reproduced image, the binarization threshold manually entered by the input means is converted by the conversion means, and the conversion means Binarization is performed by the binarization means based on the binarization threshold value converted by .

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 3 show an embodiment of the invention.

FIG. 3 shows the appearance of the image reading device 1 of this embodiment.

In FIG. 2, reference numeral 1 denotes a document image reading device (hereinafter referred to as a reader), which is dedicated to a "book mode" without a so-called "sheet (through) mode." The reader 1 is always connected to external devices (not shown), such as a digital printer and a personal computer.
Communication of control signals with an external device and output of image signals from the reader 1 to the external device are performed via the interface circuit 27.

17 is a platen glass. A book document 18 is placed on the platen glass 17 with the document surface facing downward so that its right end is aligned with the leading edge of the document.

The Book R manuscript is not necessarily a bound book, but may be in the form of a sheet. 19 places the original 18 on the platen glass 17
A platen cover 31 that is brought into close contact with the top is a white reference plate for shading correction.

The optical scanning system includes a fluorescent lamp 15a of the document illumination unit 15 that illuminates the book document 18, a reflection mirror 16 that regulates the reflected light from the original fA 18, and a light from the reflection mirror 16.
A lens 14 converging onto a charge-coupled device (CCD) 12 consisting of a plurality of light receiving elements arranged in the main scanning direction
It is made up of. Optical original illumination unit 15
The right end in FIG. 2 is the initial position (reference position), and the position is confirmed by an optical position sensor (not shown).

13 is a CCD driver, 11 is a control unit, and
The configuration is shown in the figure.

In FIG. 1, 12.14 indicates the same part as in FIG.

(CCD driver 13) 23 is a CCO drive circuit, which drives the CCD as a concentration detection means.
12. 21 is an amplifier (AMP)
This amplifies the signal from CGD I2. 2
2 is a DD converter (^/D) which converts the analog output signal of the AMP 21 into an 8-bit digital signal.

(Control unit 11) 20 is a shading correction circuit, which corrects non-uniformity of the light amount of the illumination unit 15,
624 is an optimal density detection circuit as a reference density determination means, which removes the level non-uniformity (called shading) caused by the transmission non-uniformity of the lens 14 and the average sensitivity of the CCD 12 (referred to as shading). The optimum slice level value for binarization is determined from the density histogram in the area. 25 is a binarization circuit as a binarization means, which binarizes the 8-bit image signal according to the slice level for the optimum density. 26 is a selector that selects binary mode or multi-value mode. 27 is an interface circuit that compresses 8 pixels and converts 8 bits into multi-value mode. In the value mode, one pixel is made up of 8 bits. 30 is an oscillator (OSC) that generates a reference signal. 29 is a timing signal generation circuit that generates timing from the reference signal of OSC 30. The timing signal is output to the CCO drive circuit 23, ^/D 22, optimum concentration detection circuit 24, binarization circuit 25, and interface circuit CP 27. 28 is a CPU as a conversion means; The reference density determined by the optimum density detection circuit 24 corresponds to the optimum density of the reproduced image, the predetermined maximum density corresponds to the maximum density of the reproduced image, and the predetermined minimum density corresponds to the minimum density of the reproduced image. This method converts the manually generated binarization threshold based on the corresponding gradation characteristic curve.

FIG. 4 is a flowchart showing the control procedure stored in the ROM 28A.

Prior to the operation of the reader 1, commands for various modes are inputted from an external device. For example, to determine the density, set the pixel density (dots/inch = dpi) to 400.3
00 or 200, and where on the document the image reading area should be placed.

When these commands are received, control signals are output to the timing signal generation circuit 29 and selector 26 in advance to set the pixel density and reading area position/size.

When a document reading start command is manually input from an external device, it is checked in step S2 whether or not the book document 18 is in the book position, and if it is found in the book position, in step S2 the lamp is turned on. Control (No. 8 is output to turn on the lamp 15a of the document illumination unit 15. Then, in step S3, the reader 1 performs a reading density determination process, in step S4, the motor is reversed, and in step S5, , it is determined whether the optical system has returned to the book position, and as a result of the judgment, if the optical system has returned to the book position, the process moves to step S6, and in step S6, shading correction is performed.
Scanning is started in the six directions of the arrows in FIG.

From the initial position of the original illumination unit 15 to the platen glass 1
There is a distance of about 2 mm3InI11 from the leading edge of the original on the document 7, and during this time, the scanning speed of the optical system is controlled to be stabilized by a pulse motor (not shown).

Then, when the original illumination unit 15 reaches the leading edge position of the original, in step S6, a control signal enabling image signal output is output to the interface circuit 27, and the read images are sequentially sent to an external device.

Since the scanning length of the optical system is uniquely determined by the number of pulses input to a pulse motor (not shown), it is determined that reading the document is complete when the required number of pulses is output to the motor, and in step S7, The lamp 15a is turned off, image signal output is disabled, the motor is reversed, and a document reading end signal is output to an external device. By the motor reversal control, the document illumination unit 15 moves in the direction of arrow A in FIG. 2C.
Go in the opposite direction C. Then, in step S9, when the optical position sensor (not shown) detects that the motor has reached the initial position (home position), the motor is stopped. If the next document reading start command is not received from the external device during the return period of the optical system, the optical system stops at the initial position and ends the operation.

FIG. 5 shows the relationship between the specified density of the document and the slice level value. The gradation characteristic curve shown in FIG. 5 has a first point where the reference density "r89" corresponds to the optimum density normal of the reproduced image, and a second point where the predetermined maximum density corresponds to the maximum density of the reproduced image. and the second point and the lowest concentration "0".
'' and the lowest density rO of the reproduced image are formed by a line segment connecting the corresponding third point.

The user can specify the concentration in stages, and the density can be set to no.
rmal, darkl, dark part, dark part, li
There are 7 levels: light, light2, light3. The slice level value corresponding to the density normal l corresponds to a value obtained using so-called AE processing, which calculates the optimum slice level value for binarization from the density histogram in the scanned reading area.
Both the light parts are divided into four equal parts to give each density level. The image digital signal output is 8 bit data with 256 gradations.

For example, a case of a document having a reference density of "89" will be explained in comparison with a conventional example.

When the density darkl is specified, in the conventional example, the relationship between the density specification value and the slice level value is as shown by the broken line in FIG. 5, so the slice level value corresponding to the density darkl is "95." , in this example, the concentration no.
The slice level value for rmal is 189'', and the slice level value r95 corresponds to the density darkl in the conventional example.
'', the slice level value corresponding to the density darkl is "62", and it is possible to output even lighter density parts of the document.

In this way, by setting the slice level value corresponding to the optimum density value of the original as the density normal, a reference can be established for the user's density adjustment for each original.

FIG. 6 shows the relationship between the specified density of the document and the slice level value.

In comparison with FIG. 5, this is because the relationship between the designated density value and the slice level value is different. That is, the gradation characteristic curve shown in FIG. 5 has a first point where the reference density "89" corresponds to the optimum density normal of the reproduced image, and a second point where the predetermined maximum density corresponds to the maximum density of the reproduced image. The curve was made of a line segment connecting the second point and a third point where the second point and the lowest density "0" correspond to the lowest density rO of the reproduced image. The gradation characteristic curve shown in the figure has a first point where the reference density "894" corresponds to the optimum density normal l of the reproduced image, and a second point where the predetermined maximum density corresponds to the maximum density of the reproduced image. , a quadratic curve passing through the third point corresponding to the lowest density [01] and the lowest density [0] of the reproduced image.

In this embodiment, an example in which the density is designated in seven stages has been described, but it goes without saying that the density may be divided into more stages.

Biohistory Transfer 1 This embodiment is different from the other embodiments in terms of processing method. That is, in one embodiment, an AE method was adopted that scans the reading area to find the slice level corresponding to the optimum density of the document prior to image output, but in this embodiment, a sequential AE method is used, in other words, For each main scanning line, the intermediate value between the maximum density value and the minimum density value of that line is determined, and the average value of the intermediate values for several lines including that line is used as the slice level value of that line. If you use this method, you can read as many as 'a? It becomes possible to perform IA degree detection and image output in one scan.

In this case, the digital signal corrected by the shading circuit 20 is sent to the optimum density detection circuit 24 for each line.
A slice level value corresponding to the optimum density is determined manually, the value is corrected to a designated density using the CPU, and the value is set in the binarization circuit 25 to perform binarization.

[Effects of the Invention] As explained above, according to the present invention, since it is configured as described above, there is an effect that an intended gradation can be reproduced.

Figure 4 is a flowchart showing the control procedure using the CPII 28 shown in Figure 1. Figure 5 is a diagram showing an example of the relationship between the density specification value and slice level value. Figure 6 is the density specification value and slice level. FIG. 7 is a diagram showing another example of the relationship between values.

1... Original image reading device, 11... control unit, 13...CCD driver, 25...binarization circuit, 24...optimal concentration detection circuit, 28...cpu.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the structure of an embodiment of the present invention, and FIG. 3 is a diagram of an image reading device according to an embodiment of the present invention. Louis direct slice level 4 direct

Claims (1)

[Claims] 1) An image reading device having an input means for inputting a binarization threshold, comprising: a density detection means for detecting the density of a document; and a reference density determined from the density distribution detected by the density detection means. A reference density determining means to be determined, a reference density determined by the reference density determining means and an optimum density of the reproduced image are made to correspond, a predetermined maximum density is made to correspond to a maximum density of the reproduced image, and a predetermined minimum a conversion means for converting the binarization threshold inputted by the input means based on a gradation characteristic curve that corresponds the density to the lowest density of the reproduced image; An image reading device comprising: binarization means for converting into values. 2) The image reading device according to claim 1, wherein the optimum density of the reproduced image is a center density of the reproduced image density. 3) In claim 1, the gradation characteristic curve connects a first point where the reference density corresponds to the optimum density of the reproduced image and a second point where the predetermined maximum density corresponds to the maximum density of the reproduced image. An image reading device comprising a line segment, the line segment connecting the second point and a third point to which the predetermined minimum density corresponds to the minimum density of the reproduced image. 4) In claim 1, the gradation characteristic curve has a first point where the reference density corresponds to the optimum density of the reproduced image, and a second point where the predetermined maximum density corresponds to the maximum density of the reproduced image. , an image reading device characterized in that the predetermined minimum density and the minimum density of the reproduced image form a quadratic curve passing through a corresponding third point.