JPH0746837B2 - Image reader - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an image reading apparatus for converting two-dimensional optical information of a slide film, a negative film, a printed matter or the like into an electric signal by a solid-state image sensor.

(Background of the Invention) In recent years, a so-called electronic still camera in which a recording device using a small magnetic disk is integrated has been proposed, and an object is photographed by a solid-state image sensor, converted into an electric signal, and object information is recorded on a magnetic disk. I am trying.

On the other hand, with the commercialization of electronic still cameras that use magnetic disks as recording media, a service has also been proposed for recording film photographs of conventional silver salt films on the same small magnetic disk. Even if it is an image taken by using it, if a small disc on which the image is recorded is put on a reproducing device, a film photograph can be easily displayed on a television for viewing.

Therefore, when recording an image of a silver salt film on a small magnetic disk, the functions such as trimming, color balance, γ correction, and brightness adjustment while watching TV can be adjusted according to your preference. It inevitably arises as a requirement for a device for recording on a disc.

As a photoelectric conversion element used for converting an image (optical signal) of such a silver salt film into an electric signal and recording it on a small magnetic disk, a solid-state image pickup element can be made smaller and lighter than an image pickup tube. Also, it is excellent in that it does not suffer from mechanical weakness like an image pickup tube or deterioration of image quality due to aging.

(Problems to be Solved by the Invention) However, when a solid-state imaging device is used for photoelectric conversion of a silver salt film, the dynamic range of the solid-state imaging device is usually very narrow compared to the dynamic range of the silver salt film, and the film I can't convert it into an electric signal according to the light and darkness.

In other words, if you try to get the low-density portion of the silver salt film well, the high-density portion is masked by the dark current of the solid-state image sensor and the S / N ratio of the output signal deteriorates. Signal S / N of high density part of silver salt film
If the exposure amount of the solid-state image pickup device is increased to increase the ratio, the low-density portion is overexposed and the accumulation part of the solid-state image pickup device is saturated, and the S / N ratio of the low-density portion deteriorates. In particular, when photoelectrically converting a silver salt film that captures a subject with a difference in brightness, the range in which the density can be faithfully converted is limited. If you try to get the dark part out, the bright part will fly out.

On the other hand, when a two-dimensional image pickup device is used as the solid-state image pickup device, the two-dimensional image pickup device is operated by video, and the exposure amount or the γ value to the solid-state image pickup device may be determined while observing the photoelectric conversion output on the monitor TV. It is considered to use a one-dimensional solid-state image pickup device when it is desired to obtain a reproduced image which is inexpensive and has a high resolution. The use of the one-dimensional solid-state image pickup device has the following problems.

When a one-dimensional solid-state image sensor is used, an analog signal obtained by mechanically sub-scanning the one-dimensional solid-state image sensor is converted into a digital value once and stored in a semiconductor memory. The information will be read out and watched on the monitor TV. Therefore, for example, if the exposure amount is changed while watching the monitor television, the exposure amount is changed, and then the one-dimensional solid-state imaging device is scanned again to convert the film image into an electric signal. Mechanical sub-scanning of the solid-state image sensor becomes necessary,
The number of mechanical sub-scans increases.

In order to solve the problem that the number of sub-scanning increases, for example, preliminary scanning is first performed to examine the density distribution of the silver salt film, and the exposure amount is determined by a microcomputer or the like. It is necessary to devise to reduce the number of sub-scans by adjusting the exposure amount so that the density of the designated portion falls within the dynamic range of the solid state rough image pickup device by designating.

Further, in the case of a negative film, since the slope of the γ value changes especially in a high density portion, the analog signal γ is converted into an analog γ value before the analog signal from the solid-state image sensor is converted into a digital signal.
It is necessary to include a circuit for changing the value to reduce the quantization noise, and several types of changing the γ value are required. Therefore, it is also necessary to determine the γ value at the pre-scanning stage.

Thus, when using the one-dimensional solid-state image sensor,
There is a problem that the device configuration is complicated and the operation is complicated, and that it takes time to perform the process while watching the monitor TV.

(Object of the Invention) The present invention has been made in view of such conventional problems, and has a wide dynamic range capable of covering the dynamic range of a silver salt film even when a one-dimensional solid-state imaging device is used. It is an object of the present invention to provide an image reading device capable of obtaining a photoelectric conversion output.

(Summary of the Invention) In order to achieve this object, according to the present invention, the light amount of a light source is changed, main scanning is performed a plurality of times under the different light amount, and an electric signal from a one-dimensional solid-state imaging device is added. As a result, a photoelectric conversion output having a substantially wide dynamic range is obtained.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention.

First, the structure will be described. 1 is a lighting lamp, 2 is a diffusion plate for suppressing unevenness of light amount of the lighting lamp 1 to create a surface light source, 3 is a silver salt film such as a slide film or a negative film, 4 is a lens, Reference numeral 5 is a diaphragm, and 6 is a one-dimensional solid-state imaging device. The one-dimensional solid-state imaging device 6 has a plurality of light-receiving pixels arranged in a horizontal row and mechanically performs sub-scanning in a direction (sub-scanning direction) indicated by an arrow G perpendicular to the arrangement direction (main-scanning direction) of the light-receiving pixels. And converts the two-dimensional image information of the silver salt film 3 into an electric signal.

Reference numeral 7 is an A / D converter for converting the photoelectric conversion output A of the one-dimensional solid-state imaging device 6 from an analog signal to a digital signal, 8 is an adder, 9 is a semiconductor memory, and 12 is an exposure amount control circuit. Here, the one-dimensional solid-state imaging device 6 reads the signal a plurality of times at the same position, and the exposure amount control circuit 12 controls the exposure amount by controlling the accumulation time in the one-dimensional solid-state imaging device 6. , In the above-mentioned reading of a plurality of signals at the same position, for example, if the exposure amount at the time of the first reading is set to 1, it becomes 1/2, then 1/3, 1/4 at the time of the next reading. As described above, the exposure amount is changed.

The semiconductor memory 9 needs to have a storage capacity corresponding to pixel information obtained by one-time scanning of the one-dimensional solid-state image pickup device 6, but as described above, the signal is read a plurality of times for the same pixel. However, the storage capacity is large in order to store all of this information. Therefore, in the embodiment of the present invention, as will be described later, it is sufficient that a final output has a value obtained by adding outputs obtained by changing the exposure amount to the same pixel and reading out a plurality of times. On the other hand, the storage capacity is significantly reduced by setting the capacity that can store the value obtained by adding the outputs of multiple times. That is, assuming that the A / D conversion into 8 bits is performed by one reading, if the same pixel is read four times, the amount of information is 32 bits, but the added value becomes 10 bits, so the addition is performed. If the values are stored, the storage capacity does not increase so much as compared with the case where only one reading is performed for the same pixel.

The adder 8 performs an operation for adding outputs read out a plurality of times to each pixel and storing the added outputs in the semiconductor memory 9. Specifically, first, the semiconductor memory is reset. Every time, the adder 8 calls the output of the A / D converter 7 and the value stored in the semiconductor memory 9 of the pixel for the output of the A / D converter 7 and adds them, and then adds the value to the output of the A / D converter 7 described above. The new value of the pixel is stored in the semiconductor memory 9. Therefore, the semiconductor memory 9 stores information obtained by adding the output signal (digital signal) obtained by varying the exposure amount of the one-dimensional solid-state imaging device 6 for each pixel output. The addition information of the output signal obtained by changing the exposure amount corresponds to the fact that the dynamic range of the photoelectric conversion output is substantially expanded, as will be described later.

As described above, the one-dimensional solid-state imaging device 6 is read at the same position by changing the exposure amount a plurality of times, and the value obtained by adding the output read a plurality of times to each pixel is stored in the semiconductor memory 9. After that, the one-dimensional solid-state image pickup device 6 is moved by one pixel in the sub-scanning direction and the information of the new pixel is stored in the semiconductor memory 9, so that the two-dimensional image information is stored in the semiconductor memory by one sub-scanning. I can remember.

Reference numeral 10 denotes a γ conversion circuit, which digitally γ-converts a photoelectric conversion signal having a wide dynamic range read from the semiconductor memory 9. Reference numeral 11 denotes a D / A converter that converts the digital signal output from the γ conversion circuit 10 into an analog signal, and the output D of this D / A converter is provided as a video signal to a monitor television or the like.

FIG. 2 is a one-dimensional solid-state image sensor 6 in the embodiment of FIG.
FIG. 4 is a graph showing the photoelectric conversion characteristics of A, in which curve A shows the analog output of the one-dimensional fixed image sensor 6, and curve B shows the A / D
The signal digitally converted by the converter 7 is represented by an analog value.

As is apparent from FIG. 2, the one-dimensional solid-state imaging device 6
Output A has a large dark current ratio when the light intensity is low.
If the S / N ratio is low and the amount of light is large, the output will be saturated due to the saturation of the storage unit. Therefore, in the embodiment of the present invention, only the part of the output characteristic of the one-dimensional solid-state image pickup device 6, that is, the photoelectric conversion characteristic, which has a good linearity and an S / N ratio, is A / D converter 7.
A / D conversion is carried out, and the photoelectric conversion characteristic passing through the A / D converter 7 becomes a narrow range as shown by the curve B.

Here, the dynamic range is further narrowed by passing through the A / D converter 7, but in the present invention, the dynamizer range can be finally widened, so that the final photoelectric conversion output can be obtained. In order to improve the linearity of the photoelectric conversion characteristic and the S / N ratio, the A / D converter 7 performs A / D conversion only on the portion having the excellent linearity and the S / N ratio.

Next, with reference to FIG. 3, the operation of widening the dynamic range of the photoelectric conversion output according to the embodiment of FIG. 1 will be described.

First, since the output of the solid-state imaging device 6 is read after the charge obtained by the light hitting the light receiving portion is accumulated in the accumulating portion, the output from the accumulating portion indicates the intensity of the light hitting the light receiving portion as the accumulation time (exposure time). It is proportional to the value integrated by (time). For this reason,
If the storage time (exposure time) is halved, the slope of the photoelectric conversion characteristic will be halved.

In FIG. 3, each of the photoelectric conversion characteristics B2, B3, B4 is
The accumulation time, that is, the exposure time is 1/2, 1 / for the photoelectric conversion characteristic B1.
It shows the photoelectric output with respect to the light quantity of the one-dimensional solid-state imaging device that has passed through the A / D converter when changed to 3,1 / 4.

Here, in the embodiment of FIG. 1, since the photoelectric conversion output obtained each time the accumulation time, that is, the exposure time is changed is added by the adder 8 and stored in the semiconductor memory 9, the semiconductor memory 9 is stored. The photoelectric conversion characteristic obtained as the stored value of 9 is the conversion characteristic C shown by the broken line in which the conversion characteristics B1, B2, B3, B4 obtained by changing the exposure amount are added.

Thus, if the final photoelectric conversion output is the value obtained by adding the outputs of the solid-state image pickup device with the accumulation time (exposure time) changed, the dynam range of the photoelectric conversion output is substantially widened, and The conversion characteristics have a steeper slope when the light amount is smaller, so quantization noise when converting to a digital signal can be suppressed, and only the output with a good S / N ratio is added. Even when the amount is small, the S / N ratio of the photoelectric conversion output does not deteriorate.

As described above, the semiconductor memory 9 stores the photoelectric conversion signal obtained by adding the received light signals obtained by varying the exposure amount for each pixel output and substantially expanding the dynamic range, so that the one-dimensional solid-state imaging is performed. After the scanning of the element 6, the value of the semiconductor memory 9 is converted into an analog signal by the D / A converter 11 through the γ conversion circuit 10 for viewing on a television, and the color balance, γ correction, and brightness are also converted by the γ conversion circuit 10. The adjusted output of the γ conversion circuit 10 may be recorded on the same small magnetic disk as that used in the electronic still camera.

Furthermore, in the case of a silver salt film, the maximum density is limited, so when using a one-dimensional solid-state image sensor, if the dynamic range of the photoelectric conversion values added to cover the maximum density of the silver salt film is taken, All information of the silver halide film can be obtained by performing one sub-scan, and color balance, γ, brightness, etc. can be adjusted only by the γ conversion circuit without re-scanning as in the past. You can

In the above embodiment, the exposure time in the solid-state image sensor was changed to change the inclination of the photoelectric conversion characteristic. However, instead of changing the exposure time, the brightness of the illumination lamp 1 is changed, or the illumination lamp is changed. A photoelectric conversion output with a substantially expanded dynamic range can also be obtained by using a xenon tube instead of 1 to change the flashing time or controlling the diaphragm 5. Further, in the above-described embodiment, the two-dimensional solid-state imaging device can be applied as it is. Further, in the above-mentioned embodiment, the case where the silver salt film is photoelectrically converted is taken as an example, but the exposure time is changed also when the printed matter or a stationary object image is converted into an electric signal using the solid-state image sensor. By obtaining the added value of the photoelectric conversion output thus obtained, it is possible to obtain the photoelectric conversion output with the dynamic range similarly expanded.

(Effects of the Invention) According to the present invention as described above, since the main scanning is performed a plurality of times by changing the light amount of the light source and the obtained electric signals are added, the dynamics of the solid-state imaging device are substantially increased. The range can be expanded, and the S / N of photoelectric conversion signals can be spread over a wide range from the part with high film density to the part with thin film density.
The ratio can be improved.

Also, since the circuit can be almost digitalized, the adjustment part at the time of assembly is reduced, and all information can be obtained by changing the exposure and reading multiple times. Various processing operations of the film performed while it is performed become easy. Of course, since the reproduced signal when recorded on a small magnetic disk also has a wide dynamic range, a clear monitor image with an S / N ratio can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a graph showing the photoelectric conversion characteristics of the solid-state image sensor and A / D converter used in the embodiment of FIG. 1, and FIG. The figure is a graph showing the photoelectric conversion characteristics and the final photoelectric conversion characteristics obtained as the addition characteristics when the exposure time is changed. 1: Illumination lamp 2: Diffuser 3: Silver film 4: Lens 5: Aperture 6: One-dimensional solid-state image sensor 7: A / D converter 8: Adder 9: Semiconductor memory 10: γ conversion circuit 11: D / A Converter 12: Exposure control circuit

Claims (1)

[Claims] 1. A light source for illuminating a film, a one-dimensional solid-state image sensor for scanning transmitted light of the film photographed by an optical system in a main scanning direction and converting the light into an electric signal, and a light source for the light source for each main scanning. A light amount changing unit that changes the light amount to change the exposure amount that reaches the solid-state imaging device, and an adder that adds a plurality of electric signals output from the solid-state imaging device for each exposure amount converted by the light amount changing unit. An image reading apparatus comprising: a driving unit that relatively moves the solid-state imaging device and the film in a sub-scanning direction after performing main scanning a plurality of times per line.