JP2586036B2 - Image reading device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an image reading apparatus (image reader), and more particularly, to an image reading apparatus that does not require a pre-scan and a special sensor for detecting document density. And an image reader capable of adjusting image density.

The image reader of the present invention is used, for example, for reading a text document with a non-white background.

[Related Art] Conventionally, an image reading device (image reader) using a one-dimensional imaging device (CCD) has been provided.

This apparatus scans, for example, reflected light from a document placed on a document table while photoelectrically converting it by a CCD, performs predetermined signal processing on the light, and sequentially outputs image data.

When reading an image with the image reader,
In order to adjust the density of the formed image to an appropriate level, the density of the original image is read by pre-scanning, and a signal or the like is adjusted so that the density approaches the reference level, or the density of the original image is adjusted. Is detected and adjusted using sensors for detecting the density.

[Problems to be Solved by the Invention] As described above, in order to adjust the density in the conventional image reader, an operation requiring a long time such as a preliminary scan is required, or as in a density detection sensor. Special equipment was required, resulting in waste of time or cost.

An object of the present invention is to provide an image reader capable of easily performing appropriate density adjustment while eliminating such waste.

Means and Action for Solving the Problems The present invention provides a one-dimensional imaging device that performs photoelectric conversion while exposing and scanning an original image, and then performs A / D conversion and binarization processing using the area gradation method. An image reading apparatus that performs predetermined processing such as output, and stores at least one line of image data, and stores a predetermined density level of the stored one line of data with a corresponding reference density level. Calculating means for comparing and calculating a difference; adjusting means for adjusting a binarized reference voltage so as to eliminate the calculated difference; reading the storage, the calculation, and the adjustment; And a control unit that sequentially executes the image reading apparatus in parallel with the image reading apparatus.

In the above description, the predetermined density level means, for example, data obtained from light reflected from a white area (a plain background area) of a document image.

The reference density level means, for example, data obtained from reflected light from an ideal white document. The data value is 127, for example, when the output signal from the CCD is quantized by 7 bits, and the black level is “0” and the white level is “127”.

Therefore, to eliminate the difference by comparing the predetermined density level with the reference density level, for example, when the plain background area of the document is light blue and the density data of the area is a numerical value of about `` 100 '' This means that the level is made closer to “127” to make the background area of the image to be formed close to white. In the present invention, the above approach is achieved by controlling a binarized reference voltage.

The detection of the predetermined density level and the adjustment of the binarized reference voltage are sequentially executed in parallel with the image reading. For this reason, there is no need for preliminary scanning for density adjustment and no special sensor device.

Hereinafter, embodiments of the present invention will be described in the following order with reference to the accompanying drawings.

(1) Schematic configuration of image reader (2) Control means of image reader (3) Description of test pattern (4) Description of operation (1) Schematic configuration of image reader FIG. It is a typical sectional view.

A halogen lamp 2 serving as an exposure source irradiates a document 6 placed on a document glass 4. The original 6 is the original glass 4
Are placed in parallel along the original scale provided in the. A test pattern for magnification and focus adjustment or shading correction is provided on the lower surface of the end portion of the original glass 4 (see FIG. 4).
Is installed. The halogen lamp 2 includes a reflecting mirror 8 and an infrared cut filter 10.

The reflected light from the original 6 is reflected by the first mirror 12 and the second mirror 14.
And after being sequentially reflected by the third mirror 16, the lens 18
Passes through to a one-dimensional CCD (imaging device) 20.

The CCD 20 is held by the CCD holding unit 22, and its position and angle are adjusted. In addition, the CCD holding unit 22 and the lens 18 are attached to the movable base 24.

To adjust the magnification, as shown in Fig. 2,
26, the moving table 24 is moved along the guide rail 30 in the optical axis direction via the wire 28.

In addition, the focus is adjusted by moving the CCD holding unit 22 in the optical axis direction by the focus motor 32 attached to the movable base 24.

When scanning the document 6, the light source 2 and the mirrors 12 to 16 are moved in the scanning direction, as is well known.

(2) Control Unit of Image Reader FIG. 3 is a block diagram of a circuit for detecting the density of a document.

The clock generation circuit 40 supplies a necessary SH (shift pulse) signal to the image sensor (one-dimensional CCD) 20,
It is also connected to U42 and used for clock signals. The image sensor 20 converts a reflected light signal from a document into an electric signal.
The A / D converter 44 converts an analog signal from the image sensor 20 into a digital signal.

The shading circuit 46 is in the main scanning direction (line direction).
This is a circuit for correcting the unevenness in the light amount and the variation between bits (pixels) of the image sensor 20, and its timing is given by a shading signal from the CPU. The output signal from the shading circuit 46 is input to a comparison circuit 48 for binarization and a line RAM 50.

The comparison circuit 48 compares the magnitude of the image signal subjected to the shading correction with the reference signal (reference signal for binarization) selected by the selector 52, and outputs the result to the output circuit 54 in one bit. The output circuit 54 outputs a 1-bit image signal and a valid image signal to the outside.

The line RAM 50 stores the image signal subjected to shading correction for one line. The write signal is output from the CPU 42, and the CPU 42 obtains one line of image information from the line RAM 50.

The RAM 56 stores attribute information and uniform threshold information for binarization (binarization not based on the dither method). The binary or dither attribute is determined by the CPU 42 based on the image information of one line written in the line RAM 50. Further, the uniform threshold value is also determined based on the image information for one line.

The pattern generation circuit 58 generates threshold (non-uniform threshold) information in the dither method, and the threshold is (mx
n) Generated in a matrix.

The selector 52 selects threshold information for binarization to be sent to the comparison circuit 48 based on the attribute information from the RAM 56. That is, if the attribute is dither, the pattern generation circuit 58
As the threshold information,
If the attribute is binary, the data of a uniform level from the RAM 56 is transmitted to the comparison circuit 48 as threshold information.

Further to the selector 52 is transmitted binary reference voltage signal D _TH of 7 bits from the CPU 42, thereby, the reference voltage when performing binarization at a uniform level of the threshold is controlled. This control is feedback control based on the image information of one line written in the line RAM 50. For example, the image data corresponding to the background portion of the document (which is solid, but not always white) is white level. It is performed so that

Further, the CPU 42 inputs a motor signal, a ramp signal, a fixed position signal, and a command signal. Adjustment of magnification and focus is performed by the lens motor 2 via drivers 60 and 62.
6. The focus motor 32 is driven and controlled.

(3) Description of Test Pattern As shown in FIG. 4, a test pattern 7 for magnification and focus adjustment, shading correction, and the like includes an upper half white shading portion 7a and a lower half pattern portion 7b.
Consists of

Shading correction is performed after the reflected light from the uniform white test pattern 7 is photoelectrically converted by the image sensor 20 and then A / A
This is performed by reading into the D converter 44 and the shading circuit 46 and correcting the deviation between the read signal and the signal in the ideal state. It is considered that the deviation is caused by unevenness of the optical system such as the lamp 2 and the influence of variations in the characteristics of the pixels of the CCD 20. The correction data is stored in the shading circuit 46.

The pattern portion 7b of the test pattern 7 includes black patterns 7c and 7c provided on both sides, and a stripe pattern 7d provided in the center. Magnification is the distance L between the black pattern portions 7c
And calculate by comparing with a preset length. Focus adjustment is performed by the focus motor 32 so that the measured data of the density D distribution near the inner edge 7e of the black pattern portion 7c (solid line in FIG. 5) approaches the state shown by the broken line.
Move D20.

As described above, the density adjustment is performed by the apparatus according to the present embodiment.

As can be seen from the above description, in the apparatus of this embodiment, the image data having the optimum density is obtained by adjusting the binarized reference voltage simultaneously with the image reading. Therefore, neither a preliminary scan for density adjustment nor special sensors is required.

(4) Description of Operation Hereinafter, the operation of the present embodiment device will be described.

FIG. 6 is a flowchart showing the control by the control CPU 42 of the image reader, and FIG. 7 is a time chart. In the flowchart, processes that are not directly related to the main part of the present invention, such as magnification adjustment, focus adjustment, and image data output, are not shown.

The CPU 42 starts the process by turning on the power, for example, and first sets an initial state (S102).

After inputting a scan command (S104), if the slider is not at the reference position (S200), a drive signal to a slider drive motor (not shown) is generated (S201) and the first slider (halogen lamp 2 or the like) is mounted. Slider, mirror
After returning the second slider (e.g., 14) to the reference position, an off signal of the motor is generated (S202). The return is confirmed, for example, by a predetermined fixed position signal from the scanning system. Thereafter, an ON signal is generated to the exposure lamp 2 and the slider drive motor (S108, S110), and exposure scanning of the document is started.

Based on the reflected light from the white pattern portion 7a of the test pattern 7, the light emission intensity of the exposure lamp 2 is set to an optimum level (S112). For example, when an analog image signal from the CCD 20 is quantized by 7 bits (black level 0 to white level 12
In the case of (7, 128 stages), the light emission intensity of the lamp 2 is adjusted so that the maximum value of the digital image signal obtained from the reflected light of the white pattern portion 7a becomes 127.

Based on the reflected light from the white pattern portion 7a of the test pattern 7, the data for shading correction is written to the RAM of the shading circuit 46 (S114). The correction data is data for multiplying output data from the name pixel of the CCD 20 by a predetermined coefficient for each name pixel, for example,
Data obtained from the white pattern portion 7a is made uniform by the shading correction.

After the scanning reaches the leading end of the image (S116), an effective image signal is generated, and the output circuit 54 starts outputting image data.

If the automatic exposure adjustment mode is set (S118; Y
es), the image data B is synchronized with the line RAM write signal C which rises every three clocks of the SH signal A (see FIG. 7).
Is written into the line RAM 50 via the shading circuit 46 (S120).

From the written line RAM data D, density data corresponding to a white level (meaning a plain background portion, not necessarily white) and a black level (character portion) of the image, which are designated by the operator. Alternatively, density data of an automatically designated original area (for example, A4 size) or density data of a trimming area is extracted (S12).
2).

Based on the extracted density data, the binarized reference voltage signal _DTH is controlled (S124) to adjust the reference voltage of the comparison circuit 48. This adjustment is performed, for example, so that the background portion corresponding data after shading correction has a maximum value of 127 (S11).
2).

As can be seen from the time chart of FIG.
The adjustment start time based on the digitized reference voltage signal _DTH is delayed by three clocks of the SH signal A, that is, three lines of scanning, with respect to the image data B to be referred to.

If the automatic exposure adjustment mode is not set in S118, the binarized reference voltage signal _DTH is set to a predetermined value (S132). The predetermined value is, for example, the image data corresponding to the white pattern portion 7a of the test pattern 7,
Is a value corresponding to the emission intensity to be set.

When the exposure scan reaches the trailing end of the document (S126), the effective image signal is turned off, the data output from the output circuit 54 is stopped, and an off signal for the exposure lamp 2 is generated (S128). Is generated (S130), and the slider is returned to the reference position (S13).
3), an off signal of the motor is generated (S134).

In the above case, when an editing image such as trimming is designated, for example, as shown in FIG. 8, the above-described control can be executed only for the trimming area in the document area.

[Effects] As described above in detail, the present invention reads data for density adjustment in units of one line in an image reading apparatus using a one-dimensional image sensor, and based on the data,
It controls the binarized reference voltage.

As is clear from the description of the embodiment, according to the present invention, density adjustment can be performed in parallel with image reading, so that a preliminary scan and special sensors for density detection are not required.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an image reader according to an embodiment. FIG. 2 is a plan view of a mechanism for moving the lens and the CCD. FIG. 3 is a block diagram of a control circuit of the image reader. FIG. 4 is a plan view of the test pattern. FIG. 5 is a diagram of the density distribution near the inner edge of the test pattern black pattern. FIG. 6 is a flowchart showing the control of the CPU in FIG. Fig. 7 shows the CP of Fig. 3.
6 is a time chart illustrating control of U. FIG. 8 is a diagram showing a control area in the trimming mode.

Claims (2)

(57) [Claims] An image which is obtained by subjecting a document image to photoelectric conversion by a one-dimensional image pickup device while exposing and scanning, subjecting the document image to A / D conversion, performing predetermined processing such as binarization processing by an area gradation method, and outputting the image. A reading device for storing at least one line of image data; and a predetermined density level of the stored one line of data.
Calculating means for calculating a difference by comparing with a corresponding reference density level; adjusting means for adjusting a binarized reference voltage so as to eliminate the calculated difference; Control means for sequentially performing the adjustment in parallel with the image reading. 2. An image reading apparatus according to claim 1, wherein said predetermined density level is a density level of a background portion of a document.