JPS625773A - Picture reader - Google Patents

Abstract

PURPOSE:To prevent the quantization of a picture signal from the effect of the change in the lapse of time or the environment change of a device by correcting a threshold that quantizes picture information by a reading output in a state that a film is not exposed. CONSTITUTION:With setting a microfilm F and performing the read in operation of a line sensor 2 without lightening, a data X0 that becomes a reference signal for base density is fetched in a CPU10. With lighting a lamp 1, and fetching in the peak value data of the picture signal at a peak value detector 4, and an approximate base density data by a base density detector 14 to the CPU10, an approximate base density typical value X1 and the peak value density typical value X2 of the picture signal are detected. With calculating a correcting base density BLX=X1-x0 and calculating a correction factor by correction curve, they are multiplied by a contrast value (X2-X1) and are outputted as a threshold information TLI. An adder 13 adds a base density value from the base density detector 14 and forms a threshold and a digital picture signal 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 measured by a CCD.
I: is detected by the image sensor 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. death.

However, the density of images recorded on microfilm varies depending on shooting conditions and other factors. Therefore, using a fixed threshold? If you convert it into a value, the output image will be dark or blurred.

This will cause inconvenience. Therefore, it is conceivable to make the threshold values different by determining the recorded image density or the base density of the film from the output of the imager 2 sensor. In this way, the above-mentioned inconvenience can be solved to some extent.

However, the output of the image sensor fluctuates due to aging and environmental conditions of the light source and image sensor, making it impossible to determine an appropriate threshold value.

〔the purpose〕

,+,-The invention was made in consideration of the old times, and is useful for reading images recorded on films such as microfilm! 9-1, an image reading device capable of converting an image signal to ψ1 using an appropriate threshold value is provided. That is, in the present invention, in an image reading device that exposes a film on which an image is recorded and reads the image using transmitted light of the exposed film, image information is valued by reading output when the film is not exposed to light. An object of the present invention is to provide an image reading device that corrects a threshold value for.

〔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 consisting of a CCD (charge coupled device) or the like via an optical system consisting 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 from the photointerrupter 43 as the carriage 39 moves, , the photo ink printer 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
An enlarged image is also formed on a screen 47'2 as a display means through a display device 6, etc. 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.

Then, the read image signal is used to print an image-shaped blank spot M on the recording paper.
If the recording paper set in the laser beam printer is vertically oriented, the laser beam printer will read the half-size area surrounded by reading frame 1 and print it out; on the other hand, if the recording paper is horizontally oriented. If so, 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 FQ. 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 one scan into a plurality of blocks, and detects the peak value of the image signal of each block.

The image signal obtained by l scanning 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. Then, by setting the priority block to be N bits, one scanning line is divided into an arbitrary number of blocks each having 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 water synchronization 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, as shown in FIG. 6(5), within two adjacent HSYNC periods, that is, one main scanning period, block B
It is divided into m blocks such as LI 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 R3I 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 to Dn) and m-bit data (Do to 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 lie/sensor, and 52 indicates the threshold determination area. In this way, in order to find the threshold value, instead of using the whole reading node, it is (1) 1
A small area is defined, and only the peak values obtained from this area are valid peak values for threshold determination. As a result, even when 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 the fourth [ffl], which consists of a counter 21, two comparators 22, 23 and an AND gate 24. It consists of an inverter 25, and a counter 21 is V, 5 indicating the reading period of one screen of the image.
H, 5YN as YNC signal as synchronization signal to start counting
Count C signals. The count output of the counter 21 is compared by the comparator 22 with the address (Do to Dm') representing the area start point in the sub-scanning direction output from CpulO, and the address (Dm'+1 to Dm'+1 to
Dm) in the comparator 23, and each comparator outputs one signal from when they match. By ANDing the outputs of comparators 22 and 230 (the output of comparator 23 is inverted) using AND gate 24, a line gate signal (L, GT) is generated that is one fraction from the start point to the end point of the naria. do.

With the above-1-1, the area in the sub-scanning direction can be defined by the line game signal.

Next, an embodiment of the block address setting circuit 7 is shown in FIG. This consists of a counter 26, two comparators 27 and 28, an AND gate 29, and an in/hatter 30, and the counter 26 uses the output of the block setting circuit 5 using the I], 5YNC signal as a synchronization signal to start counting. Count a certain RSI signal. The count output is Cpul
It is compared by the comparator 27 with the first address (Do to Dn') of the block area in the main scanning direction outputted from O, and the last address of the block area (Dn'+
1-D n) by the comparator 28, and each comparator outputs a 1-digit signal when a match occurs. Comparator 2 each
By ANDing the outputs of 7°28 (the output of the comparator 28 is inverted) using the AND gate 29, the area
A block area signal with 1 fraction from the start point to the end point (
B, GT).

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 a latch circuit 9' (described later), (4) is a reset signal R3I, (5) ) is the peak data. The block address setting circuit sets the block area signal to high level when the count value of the reset signal R5I reaches data (Do to Dn') indicating the starting point of the threshold value 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 determined by taking into consideration the recording position and size of the image on the microfilm.

Set as appropriate.

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

10 is a microcomputer unit (CPU) for controlling the operation of the device. The CPU 10 outputs the latch data of the latches 9 and 15 to the clock signal CLK2, respectively.
, CLK3, and 11 is a clock control circuit, which is a circuit that creates various timing clocks that serve as operating standards for the device.

Reference numeral 12 denotes a comparator for obtaining only two image signals by comparing the image signal with a threshold value formed in a predetermined procedure.

1st I + Bell, - Koku base crawl [11' Oil out [...Output of dazzling 14 and threshold information TL work from CPU10 (Do~Dp
) and supplies a threshold value to the comparator 13.

An embodiment of the base concentration detection circuit 14 is shown in FIG. As shown in the figure, it consists of 5 up/down 1 counters and a comparator 52. 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)
Sometimes the count of the uP/down counter 51 is down, and BA? When J<sig, count up.

These situations will be explained with reference to FIG. Figure 9 shows the base level BAO (counter output), threshold level and sig (A
/D output), in which the up/dowH counter 51 counts down in the region (T), that is, in the region where BAO>siH. In the area (II), that is, the area where threshold level ≧sig>BAO, up/down
The n counter 51 receives the output state 71! of the comparator 52! , (B
When AO > s i g, count down and BAO
The count up and the count down are performed according to the state in which the count up is performed at the time of s ig. (
In the area of II[) and in terms of l) up / do
The w n 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 for loading into CPU10 by 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 1 is controlled in order to control the amount of light from the lamp.

The operation of the above circuit configuration will be explained. Figure 14 shows the CPU
2 is a flowchart showing the operating procedure of CPU 10, and the program shown in this flowchart is stored in advance in the built-in memory ROM of CPU10.

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 the data Xo, which is the reference signal for the base density.
take in. That is, a line sensor reading operation is performed in a state where no light is applied to the line sensor (S1), 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 5 image data, the lamp 1 is turned on (S3), and the line sensor 2 is activated (S4).

Then, the peak value data of the digital image signal (S i 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 (3
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 set as xl (Do~Dm') and x2 (Dm'~Dm), and the threshold value determination area is set in the subscanning direction. The starting point and ending point are y2 (Do-D
n') and yl (Dn' to Dn), data within a frame 54 shown by a dashed-dotted line out of the entire reading range 53 shown by a 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.
Create a histogram with frequency on the Y axis (S6.S8
). 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, (II) 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 described above, by dividing one scanning line into a plurality of blocks and using the peak value of each block, it is possible to sample the peak value corresponding to each character even if large characters and small characters are mixed.

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 a 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 common density in the sample data obtained by the base density detection circuit 14. level. x1'
is the base density of the film with the second base density, which is lighter in base 6 degrees than the film with the first base density for which xl was determined, and is the density level with the most sample data.

Generally, the base density of a film is not the same depending on the finishing condition of the film, etc., and the density level differs from film to film. In the graph (n), 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 density representative value X2 of the image signal are detected (C313), and the difference between these two values, that is, the value of X2-Xi, is detected. , contrast value XCT
Assume that (S l 4), this contrast value XCT differs depending on the finishing condition 8 of the film as well as the base density, 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 example, in order to make the density on the copy the same, the base density is followed.
Correction is applied to the contrast value XCT (X2-X1).

The graph shown in FIG. 12 shows a correction curve used for this correction operation. The Y-axis shows the coefficient value P for multiplying the contrast value XCT, and the X-axis shows the base density level. As the zero point (origin) moves to the right of the pitch black film through which no light passes, the film base density becomes lighter. On the X axis, D=
1. The position O is the level when the film base density D=1.0, and in this case, the threshold information is 50% of the contrast value XCT, that is, the contrast value XCT divided 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.

・N is the characteristic of a film with a high base density, and ・■ is a characteristic of a film with a light base density. Generally, 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 to D = 1.0, and the base density is
By decreasing the correction coefficient P multiplied by the contrast in the case of the standard value, and increasing the correction coefficient P in the case of the base density standard value, by increasing or decreasing the threshold value during binarization,
The densities on copies due to differences in base densities are assumed to be the same density.

However, the maximum frequency approximation base density JJ%' shown in Figure 11
The value of Xx is not always a constant value for a particular film due to variations in light intensity setting, product variations, variations in temperature of the electric circuit, etc. Therefore, in order to correct these, the above-mentioned value of XQ (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 variations due to products, electrical circuits, temperature fluctuations, etc., and to always perform arithmetic processing from sample data with high precision.

That is, in FIG. 11(I), the value obtained by subtracting the correction value xotl from the approximate base density x1, that is, BLX=X1-
Find X □ (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 X'l, 1
Also, B LX=X' t -x.

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 correction base degrees B LX (
B LK) (7) Calculate the value and make it correspond to the correction curve shown in FIG.

CPUl0 is 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 l
8).

As described above, the adder 13 adds the base density value from the base density detection circuit 14 to this threshold value information TLI 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 value information T'LI 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(m) is a graph obtained by dynamically determining the amount of transmitted light through the film base. The value of x3 is the light intensity level at the point of maximum frequency on the histogram when the lamp 1 is turned on without the film being pushed into the reading position and the light intensity is measured based on the output of the line sensor 2 at this point. However, 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 in the film 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. Furthermore, since an image with a small contrast value has a low relative resolution with respect to the signal, a good copy density can be obtained by increasing the amount of light, finding the necessary contrast value, and binarizing the image.

FIG. 15 shows the operating procedure for setting the light amount using a histogram. The program of this flowchart 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, in a state where the film is not at the reading position, for example, before the film is loaded, or if the film is loaded, after the film has been rewound, the lamp 1 is turned on at a reference light intensity (S31). And line sensor 2
to start reading (532), find the peak value of the output of the line sensor 2 (S33), and create a histogram of this peak value (S34). When the reading operation for a predetermined number of times is completed (S35), the line sensor reading is stopped (536), and X3 (m in FIG. 11) is detected from the created histogram (S37).

Thereafter, the filter 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 (a) is created (S41).When the reading for a predetermined time is completed, the peak value of the output of the line sensor 2 is captured (S40).
42) Stop reading and move the line sensor back (
S43). From the created histogram, X3' (first
■) in Figure 1 is detected (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).
), a histogram is created (S41). After reading for a predetermined time (S42), the reading is stopped (543), and X3' is detected from the histogram again.
(Sn2), X3. ! :Compare X3' (346)
. This operation is repeated until x3≦X3', and
If 3≦X3', the amount of light at that time is stored. This amount of light is the amount of light that enables the above-mentioned high-resolution reading, and the film image is read with this amount of light. Note that when detecting the amount of light transmitted through the film, the film may be moved instead of moving the line sensor.

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

Further, since a sample area of image density for which the threshold value cannot be determined is defined, and data in a non-image area of the film is invalidated, the threshold value is not influenced by anything other than the image.

In addition, since the image density sample is obtained from 9 individual blocks by dividing one scanning line into multiple blocks, large 1
A good threshold value can be determined even in an image containing a mixture of 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.

Although the present embodiment has been described using the reading of microfilm as an example, the present invention is similarly applicable to reading images of other films such as 35 mm film. 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 quantizing image information is corrected based on the readout output when the film is not exposed to light, so that the quantization of the image signal is affected by changes in the device over time, environmental conditions, etc. You can prevent yourself from being influenced.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a microfilm reading device to which the present invention is applied, FIG. 2 is a block diagram showing an example of a circuit for processing a read image signal, FIG. 3 is a diagram showing a threshold value determination area, and FIG. Figure 4 is a block diagram of the line address setting circuit.
Figure 5 is a block diagram of the block address setting circuit, and Figure 6 is a block diagram of the block address setting circuit.
7 is a diagram showing the operation of dividing one scanning line, FIG. 7 is a diagram showing the peak value capture operation, FIG. 8 is a block diagram of the base density detection circuit, and FIG. 9 is a diagram showing the operation of the base density detection circuit.
FIG. 10 is a diagram showing data acquisition from the threshold determination area;
Figures 11 (I), (II), and (m) are diagrams showing examples of histograms, Figure 12 is a diagram showing the relationship between base density and correction coefficient, and Figure 13 is a diagram showing the relationship between spatial frequency and contrast. , FIG. 14 is a flowchart showing the operating procedure for determining the threshold value, and FIG. 15 is a flowchart showing the operating procedure for determining the light amount, where 1 is a lamp, 2 is a line sensor, 4 is a peak value detection circuit, and 6 is a line 7 is a block address setting circuit, 10 is a CPU, 12 is a comparator, and 14 is a base density 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 transmitted light of the exposed film, determining a threshold value for quantizing image information based on the read output when the film is not exposed to light. An image reading device characterized by: