JPS625774A - Picture reader - Google Patents

Abstract

PURPOSE:To perform appropriate quantization without being affected by the kind or the developing state of a film by deciding a threshold for the quantization with picture density to be read and the base density of the film. CONSTITUTION:With setting a microfilm F, lightening a lamp 1 and fetching in the peak value data of a digital picture signal at a peak value detector 4 and an approximate base density data at a base density detector 14 to a CPU10, an approximate base density typical value X1 and a peak value density typical value X2 of the picture signal are detected. Correction is applied on a contrast value (X2-X1) to equalize density on a copy due to the difference of the base density, and a threshold information TLI that is set as the reference of the threshold for the binary-coding of the picture signal is supplied to an adder 13. The adder 13 forms the threshold adding the threshold information TLI with the base density value from the base density detector 14 and the digital picture signal from an AD converter 3 is binary-coded by a comparator 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an image reading device that exposes a film on which an image has been recorded and reads the image using transmitted light from the exposed film.

[Prior art]

2. Description of the Related Art Conventionally, an apparatus has been proposed in which a large amount of information such as documents is recorded at high density on a microfilm, and when necessary, an image recorded on the microfilm is read and recorded on a recording paper.

In such a device, the microfilm is exposed to light by a light source, and the brightness and darkness of the light transmitted through the microfilm is determined by COD.
It is detected by an image sensor such as , and output as an electrical image signal.

In order to convert the read output image signal into a binary code representing white and black, for example, the image signal is generally compared with a predetermined fixed threshold value. However, the density of images recorded on microfilm varies depending on photographing conditions and the like. Therefore, if binarization is performed using a fixed threshold value, the output image will become dark or blurred, resulting in the inconvenience. Therefore, it is conceivable to make the threshold value different depending on the density of the recorded image. In this way, the above-mentioned inconvenience can be solved to some extent.

However, in films such as microfilm, the base density differs depending on the type of film, and for example, even if the image density recorded on the film is the same,
Different base densities result in different image densities, that is, different contrasts. Therefore, if the threshold value is determined only based on the image density recorded on the film, images near the base density may not be binarized accurately.

〔the purpose〕

The present invention has been made in view of the above points, and when reading an image recorded on a film such as a microfilm,
The threshold value for quantizing the image signal is set to an appropriate value, thereby making it possible to read an image suitable for film. That is, the present invention is an image reading device that exposes a film on which an image is recorded and reads the image using the transmitted light of the exposed film, and quantizes the read image information based on the density of the image to be read and the base density of the film. The present invention provides an image reading device that determines a threshold value for the image reading.

〔Example〕

Hereinafter, the present invention will be explained in detail based on preferred embodiments.

FIG. 1 is a schematic diagram of a microfilm reading device to which the present invention is applied.

In the figure, frames 31a and 31b of film F are
It is illuminated by light emitted from a halogen lamp 32 and focused by a condensing lens 33. Each image of the frames 31a and 31b of the film F thus illuminated is scanned by a one-dimensional licensor 36 composed of a COD (charge coupled device) or the like via an optical system composed of an imaging lens 34 and a fixed mirror 35. Image is formed on a surface. This one-dimensional licensor 36 is fixed to a carriage 39 that can reciprocate while being guided by a pair of parallel guides 37 and 38. Furthermore, since the carriage 39 is fixed to a wire 40 that makes the rotation from the motor 41 a linear motion, the one-dimensional line sensor 36 is driven by the motor 41.
moves in the sub-scanning direction perpendicular to its main-scanning direction,
Read image information. The image signal obtained by reading the image in this manner is binarized and output.

A photointerrupter 43 that detects the start of reading scanning is arranged on the main body side of the apparatus, and when a light shielding plate 44 fixed to the carriage 39 blocks the light of the photointerrupter 43 as the carriage 39 moves, the photointerrupter 43 detects the start of reading scanning. 43 generates a read scan start timing signal.

On the other hand, a switching mirror 45 is arranged between the imaging lens 34 and the fixed mirror 35, and a switching mirror 45 is arranged between the imaging lens 34 and the fixed mirror 35.
and 4b, the switching mirror 45 and the projection lens 4
The image is also enlarged and formed on a screen 47 as a display means via a display device 6 or the like. On this screen 47, a reading frame 1 for a half-size image and a reading frame 2 for a full-size image are printed.

If the recording paper set in a laser beam printer (not shown) that forms an image on the recording paper using the read image signal is vertically long, the laser beam printer reads the half-size area surrounded by the reading strip 1 and prints the image. output,
On the other hand, if the recording paper is horizontally long, the laser beam printer reads the full size area surrounded by the reading frame 2 and prints it out.

FIG. 2 shows a block diagram of a circuit for setting a threshold value used to binarize the analog image signal of the line sensor.

In this embodiment, the image set at the reading position of the reading device is read twice. Then, the threshold value for binarizing the image signal is determined using the data obtained from the line sensor during the first reading, and the image information output from the line sensor during the second reading is determined using the first reading data. Binarize using the set threshold.

In FIG. 2, reference numeral 1 denotes a lamp, which exposes the object (microfilm) F. Reference numeral 2 denotes a line sensor made of COD or the like, which reads an image of the subject using light transmitted through the microfilm F. The amount of light emitted from the lamp 1 is controlled according to the base density of the film to be read by controlling the amount of electricity supplied to the lamp 1 by a lamp light amount control circuit 16.
A line sensor 2 is made to read a subject image in an optimal state.

3 is an analog-digital converter, and line sensor 2
The analog image signal of is converted into a digital signal of Nb1t representing the density of each pixel.

4 is a peak value detection circuit that detects the peak value of the bright level of the image signal. This peak detection circuit 4 divides the image signal obtained by l-scanning into a plurality of blocks, and detects the peak value of the image signal of each block.

The image signal obtained by one scan is sent to the block setting circuit 5.
The image is divided into blocks by a predetermined number of pixels.

The block setting circuit 4 is a circuit that divides one scanning line into several blocks, and uses horizontal synchronization signals H and 5YNC synchronized with each reading scan of the line sensor 2 as synchronization signals to start counting. It is a circuit. and.

By setting the unit block to be N bits, one scanning line is divided into an arbitrary number of blocks every N bits.

FIG. 6 shows the operation of dividing one scanning line by this block setting circuit 4. In FIG. 6, (1) is the vertical synchronization signal V
SYNC, and this VSYNC is a signal synchronized with the start of reading one screen by the line sensor 2. (2) is a horizontal synchronizing signal H3YN, and this HSYNC is a signal synchronized with each main scan of the line sensor 2. The block setting circuit 4 has an N-bit counter frequency divider circuit that is cleared by HSYNC, counts the clock CLKI from the clock control circuit 11, and receives a reset signal R every N counts.
3I is output to the peak value detection circuit 4 as shown in FIG. 6(4). Therefore? 1>6 As shown in FIG. 5, two adjacent HSYNC periods, ie, one main scanning period, are divided into m blocks such as blocks BLI to BLm. The number of divisions m is appropriately set in consideration of the size of characters, symbols, etc. of the recorded image on the microfilm.

As described above, by using the output of the block setting circuit 4 as the reset signal R5I of the peak value detection circuit 4, the peak value detection circuit 4 always detects the peak value for each block.

6 is a line address setting circuit, which is a circuit for setting an address area in the sub-scanning direction.

Further, 7 is a block address setting circuit, which is a circuit for setting the block area being scanned. CpulO to line address setting circuit 6 and block address setting circuit 7
By presetting n-bit data (Do-Dn) and m-bit data (Do-Dm), an image area as shown in Fig. 3 necessary to find the threshold for binarizing the image signal is created. (Threshold value determination area). In FIG. 3, 51 indicates the entire reading range of the line sensor, and 52 indicates the threshold value determination area.In this way, in order to determine the threshold value, not the entire reading range but a smaller area is defined, and this area Only the peak values obtained from the above are used as valid peak values for threshold determination. This results in
Even if the image size or image position on the film is non-uniform, the peak value obtained from the film portion other than the image is invalidated. It goes without saying that this area should be set to a size and position where the image will always exist.

An embodiment of the line address setting circuit 6 is shown in FIG. 4, which includes a counter 21, two comparators 22, 23 and an AND gate 24. The counter 21 is composed of an inverter 25, and counts the H, 5YNC signal using the V, 5YNC signal indicating the reading period of one screen of images as a synchronization signal for starting counting. The count output of the counter 21 is Cpul
Address (Do-Dm') representing the area start point in the sub-scanning direction output from O, ! : Comparison is made by the comparator 22, and the address (Dm'+1 to Dm
) is compared by the comparator 23, and each comparator outputs one signal from when they match. Outputs of comparators 22 and 23 (
The output of the comparator 23 (the output is inverted) is logically ANDed by the AND gate 24 to generate a line gate signal (L, GT) having a single value from the start point to the end point of the area.

As described above, the area in the sub-scanning direction can be defined by the line gate signal.

Next, an embodiment of the block address setting circuit 7 is shown in FIG. This consists of a counter 26, two comparators 27, 28 and an AND gate 29. The counter 26 uses the H, 5YNC signal as a synchronization signal to start counting, and the RS which is the output of the block setting circuit 5.
Count I signals. The count output is compared with the first address (Do to Dn') of the block area in the main scanning direction output from CpulO by the comparator 27, and is compared with the last address (Dn'+1-Dn) of the block area by the comparator 28. They are compared, and each comparator outputs a 1-value code when they match. By ANDing the outputs of the comparators 27 and 28 (the output of the comparator 28 is inverted) using the AND gate 29, a block area signal (B, GT) that has a single value from the start point to the end point of the area is obtained. Set.

As described above, the area in the main scanning direction can be defined by the block area signal.

In FIG. 2, 8 is a gate circuit which creates a two-dimensional area 52 as shown in FIG. 3 by the block area determined by the block address setting circuit 7 and the line area determined by the line address setting circuit 6. This circuit passes only the signal peak values within the area 52 among the peak values detected by the peak value detection circuit 4.

FIG. 7 shows the operation of capturing peak values using block area signals (B, GT). In FIG. 7, (1) is an image signal, (2) is a block area signal, (3) is a clock CLK2 that determines the latch timing of the latch circuit 9, which will be described later, (4) is a reset signal R3I, and (5) is peak data. The block address setting circuit sets the block area signal to a high level when the count value of the reset signal R3I reaches data (Do to Dn') indicating the starting point of the threshold determination area. Thereby, the gate circuit 8 validates the peak value detected by the peak value detection circuit 4.

Note that this threshold value determination area is appropriately set in consideration of the recording position and size of the image on the microfilm.

Reference numeral 9 denotes a latch circuit for setting the timing for fetching the peak value data into the CPU10 using CLK2.

10 is a microcomputer unit (CPU) for controlling the operation of the device; CPU10 is a latch 9;
and 15 latch data by clock signals CLK2 and 15, respectively.
Capture in synchronization with CLK3 input. Reference numeral 11 denotes a clock control circuit, which is a circuit that creates various timing clocks that serve as operating standards for the device.

12 is a comparator for obtaining a binary image signal by comparing the image signal with a threshold value formed in a predetermined procedure.

13 is the output of the base density detection circuit 14, which will be described later, and the CPU 1.
Add the threshold information TL (Do~Dp) from 0,
This is an adder that supplies a threshold value to the comparator 13.

An embodiment of the base concentration detection circuit 14 is shown in FIG. It consists of an up/down counter 51 and a comparator 52 as shown in the figure. Output of up/down counter 51 (BA
O) is compared with the digital image signal sig from the AD converter 3, and the value P preset by CPUl0 is determined.
Add/subtract RISET. That is, BAO>Sigc7)
At times, the count of the up/down counter 51 is decreased, and when BAO<sig, the count is increased.

These situations will be explained with reference to FIG. Figure 9 - Base level BAO (counter output), threshold level and sig
(A/D output); in the region (I), that is, in the region where BAO>sig, the up/down counter 51 counts down. In the region of (II), that is, the region of threshold level ≧s i g > BAO, up
/down counter 51 indicates the state of the output of comparator 52 (B
When AO > s i g, count down and BAO
<The state where the count goes up when s i g)
Count up and count down accordingly. (m
) and at the point (rV), the up/down counter 51 stops counting and holds the previous count value.

By operating in this way, the digital image signal s
A value near the lowest level of ig can be obtained, and this value near the lowest level is used as the approximate base density. CLK3 is a sampling clock that provides the timing to take in the approximate base concentration to CPU10, and can be set arbitrarily. 15 is a sampling clock C for the approximate base concentration signal.
This is a latch circuit that is used to load data into CPU10 using LK3.

Reference numeral 16 denotes a lamp light amount control circuit, which receives instructions from the CPU 10 (
(Do to Di), the amount of electricity supplied to the lamp l is controlled in order to control the lamp light it.

The operation of the above circuit configuration will be explained. Figure 14- is the CPU
It is a flowchart diagram showing the operating procedure of CPUl0, and the program shown in this flowchart is stored in advance in the built-in memory ROM of CPUl0.

When the image frame to be read on the microfilm is set at the predetermined reading position and the reading operation is enabled, the CPU10 receives data xO, which becomes the reference signal for the base density.
take in. That is, a line sensor reading operation is performed without exposing the line sensor to light (SL), and the output xO at that time is taken in (S2). Thereafter, in order to start the first image reading for determining the threshold value for binarizing the image data, the lamp 1 is turned on (S3) and the line sensor 2 starts moving forward (S4).

Then, the peak value data of the digital image signal (S f g) and the approximate base density data are taken in from the CPU10 in the threshold value determination area set in advance as described above (S
5. S7).

For example, as shown in FIG. 10, the start and end points of the threshold value determination area in the main scanning direction are
2 (Dm' to Dm), and also set the start and end points of the threshold value determination area in the sub-scanning direction to y2 (Do to D
n') and yl (Dn' to Dn). As a result, data within the frame 54 shown by the dashed-dotted line out of the entire reading range 53 shown by the solid line is taken in as data for threshold determination.

When the first image reading is completed in this way (S9), the lamp 1 is turned off and the line sensor 1 is moved back (S12).

Then, using each of the captured data, the CPU 10 determines the threshold value for binarizing the image signal, with the density level plotted on the X axis and the Y Create a histogram with frequency on the axis (S6, S8).

1. In FIG. 5, histograms obtained from two types of films are shown by solid lines and dotted lines, respectively.

FIG. 5(I) is a histogram of the approximate base density component, and is a graph obtained by sampling the vicinity of the lowest level of the image signal by the base density detection circuit 14 as described above.

Further, (IT) is a graph obtained by sampling the peak value data within the above-mentioned threshold value determination area in the image signal, that is, in the case of a negative film, the data of the portion where the amount of light transmitted is the largest.

By the way, if you calculate the peak value for each scanning line, you will find that when large characters (characters consisting of components with low spatial frequencies) and small characters (characters consisting of components with high spatial frequencies) coexist in the same image. In this case, the peak values of large characters become sample data, and small characters become blurred or do not appear at all. Therefore, as mentioned above, by dividing one scanning line into multiple blocks and using the peak value of each block, it is possible to sample the peak value corresponding to each character even if L-sized characters and small characters are mixed. I can do it.

Furthermore, the graph (II) has bimodal characteristics; the peak on the lower side of the density level indicates the base density part, the peak on the higher side indicates the peak value part of the image signal, and the density level X2 is the first base density part. This is the location where the peak value level of the signal is greatest in the sample image area of the density film.

In the graph (I), xl is the density level showing a value close to the base density in the sample image area (referred to as approximate base density), and is the density level that is the most sample data obtained by the base intensity detection circuit 14. concentration level. x1′
is the base density of a film with a second base density that is lighter in base &a than the film with the first base density for which xl was determined, and is the density level that has the most sample data. Generally, the base density of a film is not the same depending on the finished state of the film, and the density level differs from film to film. In the graph (II), the second base density shown by the dotted line is lighter than the first base density shown by the solid line.

In the solid line histogram obtained in this way, the approximate base density representative value x1 and the peak value density representative value x2 of the image signal are detected (S13), and the difference between these two values, that is, X2-Xl Let I1 be the contrast IXCT (S L 4). Like the base density, this contrast value XCT differs depending on the finishing condition of the film, so even characters having the same spatial frequency do not necessarily have the same value. Therefore, simply dividing the above-mentioned contrast value XCT into two as a threshold value for binarizing the image signal does not result in the same density on the copy. Therefore, in this embodiment, in order to make the density on the copy the same, the contrast value XCT (X2-X 1 ) is corrected according to the base density.

The graph shown in FIG. 12 shows a correction curve used for this correction operation. A coefficient value P for multiplying the contrast value XCT is shown on the Y axis, and a base density level 4 is shown on the X axis. As the point O (origin) moves to the right of the J''L black film through which no light passes, the film base density becomes lighter.On the X-axis, the film base density becomes lighter at the position D=1.
This is the level when the contrast value is 0, and in this case, the contrast value
The threshold value information is obtained by dividing CT by 50%, that is, by dividing the contrast value XCT into two.

FIG. 13 is a graph in which contrast is plotted on the Y axis, spatial frequency is plotted on the X axis, and base density is used as a parameter.

Power is a characteristic of a film with a high base density, and ■ is a characteristic of a film with a light base density. In general, the main text of a newspaper is located in the spatial frequency band of range a in FIG. 13, and in this range a, the darker the base density, the lower the contrast value tends to be. Therefore, the standard value on the correction curve in FIG. 12 is set as D=1. If the base density is set to O and the base density is the standard value, reduce the correction coefficient P that is multiplied by the contrast, and if the base density is the standard value, increase or decrease the correction coefficient P to increase or decrease the threshold for binarization. By doing this, the densities on the copy due to the difference in the base densities are made to be the same density.

However, the value of the maximum frequency approximate base density x1 shown in FIG. 11 is not always a constant value for a particular film due to variations in light intensity settings, product variations, variations due to temperature fluctuations in electric circuits, etc. Therefore, in order to correct these, the value of xo described above (FIG. 11 (1)) is used.

The value of XQ is a data value obtained as an output of the line sensor 2 when the line sensor 2 is not irradiated with light as described above. By reading this at regular time intervals and using it as a reference value for the histogram, it is possible to absorb irregularities caused by products, electrical circuits, temperature fluctuations, etc., and to always perform calculation processing from sample data with high precision.

That is, in FIG. 11(I), the value obtained by subtracting the correction value XO from the approximate base density x1, that is, BLX=X1-x
Find □/)6 (S 15), Kono B LX is the first
is the corrected base density of a film with a base density of
The value obtained by subtracting the correction value XQ from the approximate base density X1, 1!
p, BLX:=X1-XO is the corrected base density of the film having a second base density that is lighter than the film having the first base density. These corrected pace 1 agricultural degree BLX (B
The value of LX- is determined, and the correction coefficient P is determined by making it correspond to the correction curve shown in FIG. 12 (appropriate [:1.
1 value can be found.

CPUl0 is 1 based on the histogram created in this way.
The above processing is executed and threshold information TLI, which serves as a reference for the threshold for binarizing the image signal, is supplied to the adder 13 (S 1
8).

As described in rii7, the adder 13 adds the base density value from the base density detection circuit 14 to this threshold value information TL■ to form a threshold value, and applies the threshold value to the comparator 12. In this way, a threshold value is formed that takes into account the image recorded on the film and the base density of the film, and when the image is read a second time using this threshold value, the digital image signal from the AD converter 3 is converted to 2 by the comparator 12. It is digitized and output as a binary code.

That is, the lamp 1 is turned on again (S19), the line sensor 2 is moved forward (S20), and the image is read. The analog image signal output from the line sensor 2 is converted into a digital image signal by the AD converter 3, and further, the comparator 1
In step 2, the threshold information TI, I output from the CPU 10 is compared with a threshold value obtained by adding the base density, and is binarized based on this magnitude relationship.

When the desired image has been read (S21), the lamp 1 is turned off (522), and the line sensor 2 is moved back again to the reading start position. This completes the reading of the desired image.

Incidentally, FIG. 11 (III) is a graph obtained by dynamically determining the amount of transmitted light through the film base. The value of By pushing the film into the reading position, the amount of light is reduced by enough transmission through the film base (light amount level x3'), and the relative resolution of the image signal is reduced. Therefore, while pushing the film in and moving the line sensor, perform a reading operation in an area where there is no image (for example, a non-image area such as a league part of the film), and set the light level to x3 to improve the resolution of the image signal. Maximize.

By doing this, the data for setting the light amount is sampled from the transmitted light in a predetermined range rather than from the transmitted light at one point on the film, so it is possible to prevent the light amount from decreasing due to variations in the light amount of the lamp, local dirt on the film, etc. It becomes possible to make corrections. Also, images with small contrast values.

Since the relative resolution of the signal decreases, a good copy density can be obtained by increasing the amount of light, finding the necessary contrast value, and binarizing it.

FIG. 15 shows the operating procedure for setting the light amount using a histogram. This Fuco chart program is also stored in advance in the built-in memory ROM of CPU10. Further, this light amount setting operation is executed, for example, before the image reading operation shown in FIG. 14.

First, when the film is not in the reading position, for example, before the film is loaded, or after the film has been rewound if the film is loaded, the lamp 1 is turned on at a standard light intensity (S31). Then, the line sensor 2 is driven and reading is started (532), the peak value of the output of the line sensor 2 is determined (S33), and a histogram of this peak value is created (S34). When the reading operation for a predetermined time is completed (S35), the line sensor reading is stopped (536), and X3 (■ in FIG. 11) is detected from the created histogram (S37).

Thereafter, the film is pushed in and, for example, a blank area of the film is set at the reading position (S38).

Then, the line sensor 2 is driven again to start reading and move the line sensor 2 forward (S39).
. The peak value of the output of the line sensor 2 at this time is captured (S40), and a histogram of the peak values is created (
S41). When the reading for the predetermined time is completed (S 4
2) Stop reading and move the line sensor back (S
43). X3' (■ in FIG. 11) is detected from the created histogram (S44).

Next, the magnitude relationship between the values of x3 and

Then, the line sensor 2 is read with the increased amount of light (S39), and the peak value at that time is detected (540).
), create a histogram (S41), and
After reading for a predetermined time (S42), stop the reading (543), detect X3' from the histogram again (544), compare X3 and X3' (346),
, knee (7) operation is repeated until x3≦X3', and when x3≦X3'', the amount of light at that time is memorized. This amount of light enables the high-resolution reading mentioned above. This is the amount of light, and the film image is read using this amount of light.When detecting the amount of light transmitted through the film.

Instead of moving the line sensor, the film may be moved.

As mentioned above, when reading images recorded on microfilm, the threshold value for binarizing the image signal is determined according to the image density and base density to be read, so the type of film, shooting, and development conditions are determined. It is possible to always obtain a good binary image signal regardless of the situation.

Furthermore, since a sample area of image density for determining the threshold value is defined and data of non-image areas of the film are invalidated, the threshold value is not influenced by anything other than the image.

Furthermore, since the image density sample is obtained from each block by dividing one scanning line into a plurality of blocks, it is possible to determine a good threshold value even for an image containing a mixture of large and different characters, symbols, etc.

Furthermore, since the transmitted light of the microfilm to be read is set to a predetermined value, it is not affected by the type of film, etc.
Film exposure is always performed with the appropriate amount of light.
1: In this example, the explanation was given using microfilm reading as an example.
The present invention can be similarly applied to image reading of other films such as M film, etc. In addition, the read image signal is not only binarized, but may also be multi-valued using, for example, a plurality of threshold values. can be executed. Furthermore, a two-dimensional image sensor can be used instead of the line sensor for reading.

Note that this threshold value determination operation may be performed every time each frame of microfilm is read, or, for example, when reading multiple frames of the same film in succession, the threshold value may be determined using the first frame. , the same threshold value may be used for reading subsequent frames.

〔effect〕

As explained above, according to the present invention, the threshold value for quantization is determined based on the density of the object image to be read and the base density of the film. I can do two things.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a microfilm reading device to which the present invention is applied, and FIG. 2 is a block diagram showing an example of a circuit for processing a read image signal. 3 is a diagram showing the threshold value determination area, FIG. 4 is a block diagram of the line address setting circuit, FIG. 5 is a block diagram of the block address setting circuit, FIG. 6 is a diagram showing the division operation of one scanning line, and FIG. FIG. 7 is a diagram showing the peak value acquisition operation, FIG. 8 is a block diagram of the base concentration detection circuit, FIG. 9 is a diagram showing the operation of the base concentration detection circuit, and FIG. 10 is a diagram showing the data acquisition from the threshold value determination area. Figure, Figure 11 (I), (
II), (II[) is a diagram showing an example of a histogram, Figure 12 is a diagram showing the relationship between base density and correction coefficient, Figure 13 is a diagram showing the relationship between spatial frequency and contrast, and Figure 14 is a diagram showing the threshold value. 15 is a flowchart showing the operation procedure for determining the light amount, 1 is a lamp, 2 is a line sensor, 4 is a peak value detection circuit, 6 is a line address setting circuit, and 7 is a flowchart diagram showing the operation procedure for determining a light amount. Block address setting circuit, IO is CPU, 12 is comparator,
14 is a base concentration detection circuit.

Claims (1)

[Claims] In an image reading device that exposes a film on which an image is recorded and reads the image using the transmitted light of the exposed film, a threshold value for quantizing the read image information is set based on the density of the image to be read and the base density of the film. An image reading device characterized by determining.