JP3124124B2 - Image information reader - Google Patents

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, and more particularly, to irradiating an original with a light source and reading image information using light receiving means such as a CCD image sensor.
The present invention relates to a color image information reading device such as a film scanner.

[0002]

2. Description of the Related Art Conventionally, in this type of image information reading apparatus, an original is irradiated with light and reflected light or transmitted light is subjected to CC.
The image information on the document surface is read by receiving and integrating with a light receiving element such as a D image sensor.

In order to improve the S / N ratio of an output signal for the purpose of improving the image quality of an image read by an image information reading device, a process of performing reading a plurality of times and averaging has been conventionally performed. However, mere averaging alone has a limit on the amount of information that can be handled even if the S / N ratio increases, and thus there is a limit on the averaged read image quality.

In order to further improve the image quality, it is necessary to increase the resolution. However, in an image information reading apparatus for digitally processing an image, it is necessary to use an A / D converter having a large number of bits in order to increase the resolution. However, using a multi-bit A / D converter leads to an increase in the production cost of the device.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image reading apparatus which digitally processes image information and which can obtain image information of a wide dynamic range with a simple configuration. is there.

[0006]

For this reason, in the image information reading apparatus of the present invention, the image information of the document illuminated by the light source lamp whose brightness changes at a predetermined cycle is converted into C information.
In an image information reading apparatus for reading by a CD image sensor, a control means for controlling a CCD image sensor to read image information in at least two periods in which the brightness of a light source lamp is different;
Analog / digital having a maximum input level substantially equal to the maximum value of the image signal output from the D image sensor and smaller than the maximum value of the image signal intensity output from the CCD image sensor during a bright period. It is characterized by comprising a conversion means, and an addition means for synthesizing image signals of at least two periods output from the analog / digital conversion means.

[0007]

FIG. 1 is a block diagram showing a schematic configuration of an image information reading apparatus according to an embodiment of the present invention. Light source 12
Is turned on by the commercial power supply 10. Light emitted from the light source 12 enters the condenser lens 22 via the color filter 20. The light from the light source 12 is uniformly projected on the film 24 by the condenser lens 22.
In this embodiment, it is assumed that the original 24 is a transmissive film 24.

[0008]

For this reason, in the image information reading apparatus of the present invention, the image information of the document illuminated by the light source lamp whose brightness changes at a predetermined cycle is converted into C information.
In an image information reading apparatus for reading by a CD image sensor, a control means for controlling a CCD image sensor to read image information in at least two periods in which the brightness of a light source lamp is different;
Analog / digital conversion means having substantially the same maximum value of the intensity of the image signal output from the D image sensor and having a maximum input level smaller than the intensity of the image signal output from the CCD image sensor during a bright period; And an adding unit that combines the image signals of at least two periods output from the analog / digital conversion unit.

The condenser lens 2 is sandwiched between the film surfaces.
On the opposite side of 2, a projection lens 26 is provided. A CCD image sensor 30 is located at the focal position of the projection lens 26.
Are arranged, and an image of the document 24 is formed on the image sensor 30 by the projection lens 26.

In general, image sensors are roughly classified into two types, a line sensor and an area sensor. In the image reading apparatus of this embodiment, a line sensor is used. For this reason, in this apparatus, the surface of the document 24 is scanned by moving the film 24 in the direction perpendicular to the direction of the light receiving line by the line sensor. The movement of the film 24 is performed by a motor 19 controlled by a driver 18 based on a drive pulse output from a drive pulse generation circuit 65.

As described above, since the line sensor is used in the present apparatus, only a predetermined range corresponding to the line sensor needs to be illuminated with a constant brightness, and it is necessary to consider a decrease in ambient luminous intensity. Absent. On the other hand, when an area sensor is used, the entire document surface needs to be uniformly illuminated.

The CCD image sensor 30 includes a driving circuit 3
2 and driven by a TSG (timing signal generator) 34 that sends a signal to a drive circuit 32, and outputs an image signal corresponding to the projected image.

Light reception by the CCD image sensor 30 is performed as follows. The charge stored in the photodiode is once swept out by the charge clear pulse output from the drive circuit 32. After that, the stored charge is read by a data read trigger pulse output from the drive circuit 32. That is, the accumulation of electric charges in the CCD image sensor 30 is started after the input of the electric charge clear pulse, and the accumulated electric charges are output as data by the input of the data readout trigger pulse.

The image signal output from the CCD image sensor 30 is suppressed by a sample-and-hold circuit 41, for example, to reset noise of the CCD image sensor 30, amplified with a predetermined gain, and output to an A / D converter 45. . The image signal digitally converted by the A / D converter 45 is stored in the line memory 70.

In the image reading apparatus of the present invention, information of one line of the document is scanned twice. The image signal obtained by the first scan is stored in the line memory 70,
The image signal obtained by the second scan is added to the adder 75. The image signal added by the adder 75 is subjected to processing such as negative / positive inversion and contrast enhancement by an LUT (lookup table) 50,
The output port 82 outputs the image data to the image data receiving device 100 such as a computer or a workstation.

The digital signal is processed by a CPU (central processing unit) 60, a DMA (direct memory access) 5
2 is controlled. When transferring image data,
It is necessary to perform high-speed data transfer exceeding the processing speed of the CPU. For this reason, in the image information reading apparatus of this embodiment, the output of the digitally converted image signal is
52, using hardware. The host controller 200 is for inputting drive commands for driving the film and the entire apparatus.

Next, control of the light receiving period of the CCD image sensor 30 according to the present invention will be described. In this apparatus, a normal commercial power supply (AC) is used as the power supply 10 of the light source. As shown in FIG. 2, the AC power supply periodically repeats positive and negative voltage values based on 0V. Accordingly, the brightness of the light source 12 fluctuates at twice the power supply frequency. When the voltage value becomes maximum, the brightness of the light source 12 becomes maximum, and when the voltage value becomes 0, the brightness takes a minimum value.

In the present case, a zero-cross detection circuit 15 is connected to the power supply 10 to detect a change in the voltage value of the power supply 10. The zero-cross detection circuit 15 detects a change in the phase of the power supply voltage and outputs a synchronization signal. That is, as shown in FIG. 2, the pulse is output at the point where the voltage value of the power supply 10 becomes 0 V, that is, at the points where the phase of the power supply voltage waveform is 0 degree and 180 degrees.

The CCD output from the timing signal generation circuit 34 based on the synchronization signal from the zero cross detection circuit 15 and the clock pulse output from the clock 36
The driver 32 is controlled by the image sensor charge accumulation control signal.
Thus, a charge clear pulse and a data read trigger pulse are output to the CCD image sensor 30, and input / output of image signals by the CCD image sensor is controlled.

In the present invention, the light receiving (scanning of the original) by the CCD image sensor 30 is controlled to be performed twice for one line of the original. The two scans are set to a period in which the light amount of the light source 12 is the largest and a period in which the light amount is the smallest. At this time, the intensity of the output signal of the CCD image sensor 30 is set so that the output level V2 during the period when the light source is dark is almost the maximum input level of the A / D converter. With this setting,
Since the output V1 of the CCD image sensor 30 during the period when the light source is bright exceeds the maximum input level, the output of the A / D converter is saturated. FIG. 3 and FIG. 4 are diagrams showing the output of the A / D converter during the period when the light source is bright and during the period when the light source is dark. The output when a step-like gray scale chart is used as a document is shown. The left of the figure corresponds to the dark part of the scale chart, and the right corresponds to the bright part. Note that an 8-bit A / D converter is used.

In FIG. 3, when the output level of the CCD image sensor 30 exceeds the maximum input level of the A / D converter, the output of the A / D converter becomes the maximum value of 25.
It is 5. On the other hand, in FIG. 4, the output of the A / D converter has a stepped shape corresponding to the scale chart.

The output of the A / D converter of the image signal obtained during the period when the light source is brightest has the maximum value V1 '. This output value is stored in the line memory 70. Next, the output of the A / D converter of the image signal obtained during the period when the light source is dark is combined with the signal stored in the line memory 70 by the adder. A / D of image signal when light source is dark
The converter output signal has a maximum value V2 '. The image signal obtained during the period when the light source is dark is combined with the signal stored in the line memory by the adder. FIG. 5 shows the composite signal of FIGS. 3 and 4.

As is apparent from the figure, the steps of the stairs are larger in the dark part of the image than in the case of FIG. 3 or FIG. is there. The output value is 0 to 51.
1, which is data equivalent to 9 bits. In addition, the data in the dark part is enlarged and captured.

The way the human eye perceives the brightness has a logarithmic characteristic. That is, the human eye has high resolution for dark objects, but not so high for bright objects. Therefore, when an image signal is output by a video camera or the like, so-called γ correction is performed. The input / output characteristics of the CRT are about γ = 2.2.
Therefore, in the video camera, γ is set to about 0.45 (= 1 / 2.2) in order to reversely correct this. Therefore, conventionally, the output of the A / D converter is further input to the gamma correction circuit for processing. The γ correction circuit is a circuit whose input and output are nonlinear, and is an analog circuit including a diode, a transistor, and the like.

In the present invention, the image signal shown in FIG. 5 obtained by the above-described method is not only data equivalent to 9 bits, but is also obtained by enlarging data of a dark portion having a visually high resolution. Can be captured. Therefore, the same effect as when gamma correction is performed can be obtained. In other words, the output of the A / D converter can be subjected to correction equivalent to γ correction only by addition by a digital circuit. Therefore, the image signal can be processed without passing through the nonlinear circuit, and the characteristics thereof are stable.

In the above embodiment, the original is irradiated with light,
Although a film scanner that receives transmitted light with a line sensor has been described, it goes without saying that the present invention is also applicable to a scanner that receives reflected light from a document. Further, the light receiving sensor is not limited to the line sensor, and the present invention is applicable to an area sensor.

In the above embodiment, an AC power supply is used as the power supply, and the reading is performed twice using the change in the brightness of the light source.
The same effect can be obtained even if the gain of the sample and hold circuit is changed by two readings.

[0028]

As described above, according to the image reading apparatus of the present invention, an image signal having a wide dynamic range can be obtained even if an A / D converter having a low resolution is used. Further, a stable signal output can be obtained at lower cost than when the gamma correction circuit is configured by an analog circuit. Further, an image is read using the fact that the light quantity of the light source lamp changes with the periodic fluctuation of the power supply. Since image information can be read by turning on a light source with a general commercial power supply (AC), a stabilizing power supply circuit that is expensive and generates a large amount of heat is not required. When a plurality of color filters are selectively inserted into the optical path to read image information for each color component, the light amount of the light source easily changes while the light receiving time of the CCD image sensor is fixed at a fixed time, and The difference in spectral sensitivity between the light source and the CCD image sensor can be corrected.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart showing a change in brightness of a light source, a light receiving period of a CCD image sensor, and movement of a film.

FIG. 3 is a diagram illustrating an output value of an A / D converter when a light amount of a light source is large.

FIG. 4 is a diagram illustrating output values of an A / D converter when the light amount of a light source is dark.

FIG. 5 is a diagram showing a combined output of the A / D converter shown in FIGS. 4 and 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Commercial power supply 12 Light source 15 Zero cross detection circuit 30 CCD image sensor 34 Timing signal generation circuit 70 Line memory 75 Addition circuit

Claims (1)

(57) [Claims] 1. An image information reading apparatus for reading, by a CCD image sensor, image information of a document illuminated by a light source lamp whose brightness changes at a predetermined cycle, comprising: Control means for controlling the CCD image sensor to read information; and a light period in which at least the maximum value of the intensity of the image signal output from the CCD image sensor in the dark period is at least one of the at least two periods. Analog / digital conversion means having a maximum input level smaller than the maximum value of the intensity of the image signal output from the CCD image sensor; and outputting the image signal for at least two periods output from the analog / digital conversion means. An image information reading device, comprising: an adding means for combining.