JPH0865467A - Image scanner - Google Patents

Abstract

PURPOSE: To reflect all picture element inputs in the sub-scanning direction goo an output by using a control means so as to vary the aperture size of a line sensor even when the resolution in the sub-scanning direction is revised into low resolution. CONSTITUTION: This scanner is provided with a line sensor 1 reading optically an original, a drive means 7 driving the line sensor 1 in the subscanning direction, a storage means 10 transferring &l? output of the line sensor 1, and a control means 5 controlling the line sensor 1 and the drive means 7. The control means 5 controls the line sensor 1 and the drive means 7 so as to vary the aperture size of the line sensor 1. Then the drive speed of the drive means 7 in the subscanning direction is changed to change the area for scanning the original per an integration time so as to vary the resolution. Thus, the drive speed of the drive means 7 is changed stepwise depending on the resolution to reflect all picture element inputs in the subscanning direction to an output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image scanner capable of changing the resolution in the sub-scanning direction.

[0002]

2. Description of the Related Art In an image scanner, an input image light beam that reaches a CCD line sensor by reflection or transmission from an original is photoelectrically converted into an electric signal (analog signal) by the CCD line sensor. Analog signal is A / D
It is digitally encoded by the converter, and is taken into the memory by the CPU.

The longitudinal direction of the CCD line sensor is generally called the main scanning direction. The moving direction of the CCD line sensor is called the sub-scanning direction. To capture an original, the stepping motor moves to the next capture position in the sub-scanning direction to capture one line in the main scanning direction. Then, the above operation is repeated to complete one image.

When all the data for each step of the stepping motor is used, the maximum resolution of the scanner is obtained. In order to obtain a resolution lower than the maximum resolution (when changing the resolution in the sub-scanning direction), the resolution has been conventionally changed by simple thinning. FIG. 4 exemplifies a case of obtaining a resolution that is ¼ of the highest resolution. In FIG. 4, 4
By capturing the output of the CCD line sensor (the line output described as effective in FIG. 4) at a rate of once per step, a resolution of 1/4 of the maximum resolution is realized.

[0005]

In the conventional simple thinning-out shown in FIG. 4, there is a problem that the input image light ray in the thinned-out line is not reflected in the output at all. That is, the CCD line sensor is
3a, ..., When the output of the CCD line sensor is taken in once every four steps, the lines 1b, 1
There is a problem that image input in c, 1d, 2b, 2c, 2d, ... Is ignored.

The present invention has been made in view of the above problems, and an object thereof is to reflect all pixel inputs in the sub-scanning direction in the output even when the resolution in the sub-scanning direction is changed to a low resolution. And

[0007]

In order to achieve this object, an image scanner of the present invention comprises a line sensor for optically reading a document, a driving means for driving the line sensor in the sub-scanning direction, and a line sensor for driving the line sensor. A storage unit that transfers and stores the output, a control unit that controls the line sensor and the driving unit, and a control unit that controls the line sensor and the driving unit so that the aperture size of the line sensor can be changed. Is configured.

[0008]

In the image scanner having the above structure, by changing the aperture size of the line sensor, even if the resolution in the sub-scanning direction is changed to a low resolution, all pixel inputs in the sub-scanning direction are reflected in the output. can do.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

When the integration time of the CCD line sensor is constant, the driving speed of the stepping motor, which is a driving means in the sub-scanning direction, is changed to scan the original area per integration time (hereinafter referred to as an aperture). The resolution can be changed by changing (. In this case, there is a problem that the driving speed of the stepping motor cannot be continuously changed because the driving system of the stepping motor has a resonance point.

When the driving speed of the stepping motor is constant, the integration time of the CCD line sensor is changed to
The resolution can be changed by changing the aperture. In this case, the lower the resolution, the longer the integration time and the saturation of the CCD line sensor.

In order to satisfy the requirement that the CCD line sensor does not saturate and the resonance point of the drive system of the stepping motor is avoided, the present invention is carried out as follows. That is, by changing the driving speed of the stepping motor stepwise according to the resolution, even when the resolution is changed to a low resolution, all pixel inputs in the sub-scanning direction are reflected in the output. Hereinafter, description will be given with reference to the drawings.

FIG. 1 is a block connection diagram showing an embodiment of an image scanner according to the present invention.

In FIG. 1, an input image light beam obtained by reading an original (not shown) by reflection or transmission is supplied to a CCD line sensor 1. The input image light beam is photoelectrically converted into an electric signal (analog signal) by the CCD line sensor 1. The analog signal is digitally encoded by the A / D converter 2, and the CPU 5 captures it in the RAM 10 via the image processing circuit 3 and the FiFo buffer 4.

When the reading of one line is completed, the stepping motor 7 is controlled by the CPU 5 to move the CCD line sensor 1 to the next taking-in position in the sub scanning direction. The CPU 5 drives and controls the stepping motor 7 via the stepping motor drive circuit 8. After that, one line is read in the main scanning direction, and the stepping motor 7 moves to the next position. By repeating this, the entire one original is read.

When all the read data of each step of the stepping motor 7 is used, the scanner 14
Will be the highest resolution of. In this embodiment, the maximum resolution of the scanner 14 is 1200 dpi. The read image data is transferred from the RAM 10 to the bus line 11 and SCSI.
It is output to the external host computer 13 via the circuit 6.

When a resolution lower than the maximum resolution is obtained (when the resolution in the sub-scanning direction is changed), the CPU 5 causes the CPU 5 shown in FIG.
It operates according to the program shown in the flow chart.

When the program starts, the resolution is first designated (step S1). Next, the speed at which the stepping motor 7 drives the CCD line sensor 1 is obtained by referring to a table (described later) from the designated resolution (step S2). The integration time of the CCD line sensor 1 is obtained from the driving speed obtained by referring to the table and the resolution designated in step S1 (step S3). In step S3, the following calculation is performed.

Line width of one line (mm / dot) = 25.4 (mm / inch) / designated resolution (dot / inch) (1) Moving speed (mm / sec) = 21.17 (μm / p) / driving speed (p / sec) (2) integration time (sec / dot) = line width of one line (mm / dot) / moving speed (mm / sec) ... (3) where: p indicates the number of pulses.

Since the maximum resolution is 1200 dpi, the moving distance per pulse of the stepping motor 7 is 25.4 (mm / inch) / 1200 (p / inch) = 21.17 × 10 ⁻³ (mm / p) ) ... (4).

Then, after the image reading operation is performed (step S4), the process returns to step S1 to prepare for the next reading operation.

As shown in Table 1, the table is calculated in advance at the design stage and written in the ROM 9.

[Table 1] This table is obtained according to the flowchart of FIG. Although the flowchart of FIG. 3 is calculated in advance in the design stage and written in the ROM 9, it may be calculated by the CPU 5 and stored in the RAM 10 when the scanner 14 is activated.

When the program starts, the variables and the like are first initialized (step S31). The shortest integration time of the CCD line sensor 1 in this embodiment is
2.176 ms. Therefore, the driving speed of the stepping motor 7 when reading at a resolution of 1200 dpi is
It is 459.6 pps (= 1 / 2.176 ms).

Next, the driving speed is multiplied by 2 ^1/3 (step S32). Here, 459.6 × 2 ^1/3 = 579.0 pps 1200/2 ^1/3 = 952 dpi is calculated (step S33). From now on, 952d
Below pi, it should be 579.0 pps, so 95
At 3 to 1200 dpi, it is found that the driving speed of 459.6 pps is optimum, and this is stored in the memory (not shown) (step S34).

Up to 120 dpi, the above step S3
By repeating Step 2 to Step S34, the value enclosed in parentheses in Table 1 is 2314.8 pps, which is 95 to 119 dpi when 1/2 thinning is performed, and 48 when 1/4 thinning is performed.
~ 59 dpi, 24 to 29 dpi if 1/8 thinning is performed
It indicates that the reading can be performed at the resolution of.

Further, at 2913.8 pps, if decimating 1/2, 76 to 94 dpi, and if decimating ¼, 3
8 to 47 dpi, 19 to 23 dpi if 1/8 thinning is performed
Reading is possible at the resolution of i.

Further, at 3766.5 pps, 60 to 75 dpi if 1/2 thinning is performed, and 3 if 1/4 thinning is performed.
0 to 37 dpi, 15 to 18 dpi if 1/8 thinning is performed
Reading is possible at the resolution of i. In the resolutions shown in parentheses in Table 1, the thinning-out reading described in the related art is adopted, but the thinning-out reading is performed because a good image can be read at a resolution of 119 dpi or less.

[0035]

As described above, according to the image scanner of the present invention, by changing the aperture size of the line sensor, even when the resolution in the sub-scanning direction is changed to a low resolution, the image in the sub-scanning direction is changed. It becomes possible to reflect all pixel inputs in the output.

[Brief description of drawings]

FIG. 1 is a block connection diagram showing an embodiment of an image scanner according to the present invention.

FIG. 2 is a flowchart showing an embodiment of an image scanner according to the present invention.

FIG. 3 is a flowchart showing an embodiment of an image scanner according to the present invention.

FIG. 4 is a conceptual diagram showing an example of a conventional image scanner.

[Explanation of symbols]

 1 CCD line sensor 3 Image processing circuit 4 FiFo buffer 5 CPU 6 SCSI circuit 7 Stepping motor 8 Stepping motor drive circuit 9 ROM 10 RAM 11 Bus line 13 Host computer 14 Scanner

Claims (2)

[Claims] 1. A line sensor for optically reading a document, a drive unit for driving the line sensor in a sub-scanning direction, a storage unit for transferring and storing the output of the line sensor, the line sensor and the drive unit. An image scanner, wherein the control means controls the means, and the control means controls the line sensor and the driving means so that the aperture size of the line sensor is variable. 2. The control unit according to claim 1, wherein the control unit changes an aperture size of the line sensor by changing a speed at which the line sensor is driven in the sub-scanning direction and / or an integration time of the line sensor. An image scanner characterized by that.