JPH04183063A - Image reader - Google Patents

Abstract

PURPOSE:To improve quality for reading images by making the dynamic range of an output signal from an image sensor to read an original equal among respective light sources. CONSTITUTION:The resistance values of resistors 102 serially connected to respective light emitting diodes 101 are gradually reduced like R1>R2>...> Rn-1>Rn<Rn+1<...<R2n-1 from the terminal part to the central part in the lengthwise direction of the light emitting diode array so as to gradually enlarge a current being supplied to the respective light emitting diodes 101 from the terminal part to the central part and to enlarge the quantity of light at the central part in comparison with the terminal part. Therefore, the dynamic range of the output signal from the image sensor to read original images is made equal among the respective light sources. Thus, quality for reading color images can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image reading device, particularly a color image reading device that reads an original image with a line image sensor by sequentially lighting up a three-color light source consisting of a fluorescent tube and a light emitting diode array. Regarding.

[Prior Art] Conventional light source switching type color document reading devices that sequentially turn on three color light sources to read document images use fluorescent tubes for both of the three color light sources, or use fluorescent tubes for the blue and green light sources. A light emitting diode array was used for the red light source, a fluorescent tube was used for the blue light source, and a light emitting diode array was used for the red and green light sources.

[Problems to be Solved by the Invention] However, in a conventional light source switching type color document reading device that uses a combination of a fluorescent tube and a light emitting diode array, the problem arises because the light distribution characteristics of the fluorescent tube and the light emitting diode array are different. If shading correction is performed using a shading correction plate that matches the light distribution characteristics of the fluorescent tube, the amount of light at the longitudinal center of the image sensor will be insufficient when the light emitting diode array is turned on, and the dynamic range of the photoelectric conversion signal will decrease. There was a drawback.

An object of the present invention is to provide an image reading device that solves the above problems.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image reading device that reads a document image by sequentially lighting up a light source consisting of a light emitting tube and a light emitting semiconductor array and detecting reflected light from the document. The present invention is characterized in that it includes a current control means for supplying a larger current to the light emitting semiconductors at the center than at the ends of the light emitting semiconductor array.

[Function] According to the present invention, the current flowing through each of the light emitting semiconductors constituting the light emitting semiconductor array is made smaller in the longitudinal center part of the light emitting semiconductor array than in the end parts, and the amount of light of the light emitting semiconductor array is lowered in the central part. By making the light source larger than the end portion, the dynamic range of the output signal of the image sensor that reads the document image is made equal between each light source.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

[Embodiment 1] Fig. 1 is a block diagram of a light emitting diode array in an image reading device according to a first embodiment of the present invention, Fig. 2 is a block diagram of the same image reading device, and Fig. 3 is a cross-sectional view of the main parts thereof. It is a diagram.

In FIG. 3, reference numeral 1 denotes the main body of the document reading device, in which a document placed on a document setting section 18 on a platen glass 17 is irradiated with a document illumination unit 15, the reflected light is reflected by a reflection mirror 16, and a lens 14 is used to display a CCD 12. It is designed to form an image. 11 is a control unit, 13 is a shading correction plate, and 19 is a document table cover.

As shown in Figure 2, this document reading device (hereinafter referred to as a scanner) is connected to external devices (digital printer, personal computer, etc.), and sends control signals to and from these external devices and images to the external devices. Output is performed via interface circuit 209.

The original is placed on the platen glass 17 so that the left end in the figure is the leading edge of the original. In addition, the original illumination unit 15 of the optical system
In Figure 3, the left end is the initial position, and the optical position sensor (
(not shown) to confirm the position. Further, with the document placed on the platen glass 17, instructions for various modes are input from an external device. For example, if the pixel density is 400dpi, 300dpi, 200dp
i, and whether the image signal should be a binary signal or a multi-value signal.

Upon receiving this, the CPU 207 issues a control signal in advance to set the pixel density and image signal.

Next, when a document reading start command is input from an external device,
The CPU 207 first outputs a signal to the light source lighting circuit 205 to sequentially blink the three light sources 204, 210, and 211. Thereafter, the original illumination unit 15 starts scanning in the direction of arrow IB in FIG. When the document illumination unit 15 reaches the document leading edge position, the CPU 207 outputs a control signal to enable image signal output to the interface circuit 209, and the read image signals are sent one after another to an external device.

Since the scanning length of the optical system is uniquely determined by the number of drive pulses that drive the pulse motor for driving the optical system, the CPU
207 determines that reading the original is complete when the required number of pulses are output to the motor, stops blinking the light source, and outputs the image signal a.
When the motor is disabled, the motor is reversed and a document reading completion signal is output to the external device. Under the motor reversal control of the CPU 207, the document illumination unit 15 moves in the direction of arrow I in FIG.
It advances in the direction A and stops when the optical position sensor indicates that it has reached the initial position. If the next document reading start command is not received from the external device during this time, the document illumination unit stops at the initial position and the operation ends.

Next, the light emitting diode array of the present invention will be explained.

Figure 4 shows the light distribution characteristics of the fluorescent tubes (210, 211), Figure 5 shows the light distribution characteristics of the conventional light emitting diode array for comparison, and Figure 6 shows the light distribution characteristics of the light emitting diode array (20
4) Light distribution characteristics, Figure 7 shows the fluorescent tube sound.

Output signal from image sensor white reading when the light is on, No. 8
The figure shows the white output signal of the image sensor when the light emitting diode array of this embodiment is lit, and FIG. 9 shows the white output signal of the image sensor when the conventional light emitting diode array is lit.

As shown in FIG. 2, three color light sources 204, 210, 21
The light emitted from 1 is irradiated onto the document surface 201. Manuscript 201
The light reflected from the surface is corrected for the light distribution of the light source and the shading of the optical system by shading correction #i, 13, and is focused by the lens 14 and imaged on the image sensor 12.

Here, the shading correction plate 13 is designed to correct the light distribution characteristics of the fluorescent tube shown in FIG. 4 and to cut off the amount of light at the longitudinal center of the tube.

However, the conventional light emitting diode array 501 that causes light emitting diode elements to emit light uniformly has a uniform light distribution as shown in FIG. Therefore, when the above-mentioned fluorescent tubes are combined and used as a light source of a color scanner, the shading correction plate 13 cuts the light amount at the longitudinal center, and as shown in FIG. 9, the output signal of the image sensor I2 at the corresponding position is becomes small, and the dynamic range of the image signal decreases.

In the present invention, as shown in FIG. 1, the resistance value of the resistor 102 connected in series to each light emitting diode element 101 is R1>R2>--->Rn-1>Rn< Rn
+1<-<R2n-1, the current supplied to each light emitting diode 101 can be gradually increased from the ends to the center by gradually decreasing the current from the ends to the center in the longitudinal direction of the light emitting diode array 204. , as shown in FIG. 6, the light quantity at the center is larger than at the ends.

With the above configuration, the light distribution characteristics of the light emitting diode array 204 are made to be similar to those of the fluorescent tubes 21111.214, so that the shading correction plate 13
As shown in FIG. 8, the output signal of the image sensor 12 becomes almost flat even when passing through the center, and the dynamic range does not decrease in the central part.

[Embodiment 2] FIG. 10 shows a configuration diagram of a light emitting diode array of an image reading device according to a second embodiment.

In this embodiment, the number of light emitting diodes connected in series to the power source is increased at the longitudinal ends of the light emitting diode array (and reduced at the center), and the current flowing through the light emitting diode elements arranged at the center is By making it larger than that of the light emitting diode element arranged at the end, the sixth
As shown in the figure, the structure is such that the amount of light at the center is larger than at the ends.

As described above, since the current supplied to the light emitting diode elements at the center of the light emitting diode array is larger than that at the ends of the light emitting diode array, a light distribution characteristic similar to that of a fluorescent tube is achieved. Even if correction is performed using a shading correction plate that matches the light distribution characteristics of the fluorescent tube, the dynamic range of the image sensor output signal corresponding to the center of the light emitting diode array decreases when the light emitting diode array is lit. ' can be prevented.

[Effects of the Invention] As described above, according to the present invention, the dynamic range of the output signal of the image sensor that reads the document can be equalized among the light sources, and the image reading quality is improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a light emitting diode array of an image reading device according to a first embodiment of the present invention, FIG. 2 is a block diagram of the image reading device, and FIG. 3 is a sectional view of the main part configuration of the image reading device. , Figure 4 is a diagram showing the light distribution characteristics of a fluorescent tube, Figure 5 is a diagram showing the light distribution characteristics of a conventional light emitting diode array, and Figure 6 is a diagram showing the light distribution characteristics of a light emitting diode array according to this embodiment. Figure 7 is a diagram showing the distribution characteristics of the daily output signal of the image sensor when the fluorescent tube is lit. Figure 8 is a diagram showing the distribution characteristic of the daily output signal of the image sensor when the light emitting diode array of this embodiment is lit. 9 is a diagram showing the distribution characteristics of the daily output signal of the image sensor when the conventional light emitting diode array is turned on. FIG. 10 is a configuration diagram of the light emitting diode array of the image reading device according to the second embodiment of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Image reading device main body, 11... Control unit, 12... Image sensor, 13... Shading correction plate, 14... Lens, 15... Lighting unit, 16... Reflection mirror , 17... Document platen glass, 18... Document placement portion, 19... Document platen cover, 101... Light emitting diode, 102... Resistor, 103... Diffusion lens array, 201... Original, 202... Amplifier, 203... A/D converter, 204... Light emitting diode array (red), 205...
・Light source lighting circuit, 206... Binarization circuit, 207... CPU, 208... Selector, 209... Interface circuit, 210... Fluorescent tube (green), 211... Fluorescent tube ( Blue), 501... Conventional light emitting diode array. <i? Four grooves - 〇 Single light l Light intensity

Claims (1)

[Scope of Claims] 1) An image reading device that reads a document image by sequentially lighting up a light source consisting of a light emitting tube and a light emitting semiconductor array and detecting light reflected from the document, the image reading device reading a document image by sequentially lighting up a light source consisting of a light emitting tube and a light emitting semiconductor array, the device comprising: An image reading device further comprising current control means for increasing the current supplied to the light emitting semiconductor in the central portion. 2) The image reading device according to claim 1, wherein the current control means supplies the current to each of the light emitting semiconductors so as to gradually increase from an end to a center of the light emitting semiconductor array. 3) The image reading device according to claim 1, wherein the resistance value of the resistor connected in series with each of the light emitting semiconductors is configured to gradually decrease from the ends to the center of the light emitting semiconductor array.