JPH0584974B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an image processing device that electrically processes a document image. [Prior Art] Conventionally, an image processing apparatus has been proposed that photoelectrically reads an image of a document such as a facsimile and electrically processes the read image signal. In such image processing apparatuses, digital processing has recently become common, as it has advantages such as ease of signal processing and resistance to the influence of external noise. Therefore, it is necessary to accurately convert the original image into a digital image signal. By the way, the conditions (density, size, etc.) of the original images to be read vary widely, and it is impossible to apply the same processing to all these original images. Therefore, a configuration is adopted in which an operator judges the state of the document image and adjusts the image processing operation based on this judgment. However, the adjustment operation is troublesome, and there are cases where good image processing cannot be performed due to incorrect adjustment. Therefore, it is conceivable to provide a function to detect the state of the document image to be read and automatically execute an image processing operation according to the document image according to the detection result. According to this, the operator's adjustment effort as described above can be saved, and even an operator who is unfamiliar with the apparatus can perform image processing to a certain extent. However, in such automatic processing, for example, the maximum and minimum values of the image density of the document are detected,
When digitizing a document image based on this, the maximum and minimum values detected from solid white, solid black, or halftone image areas are quite different from the maximum and minimum values of the entire document, and therefore , if such values are used, problems may occur such as digitization processing not being performed accurately. [Purpose] The present invention has been made in view of the above points, and it is an object of the present invention to automatically perform image processing suitable for the condition of a document image to be read, eliminate inconveniences in this automatic processing, and perform optimal image processing. The purpose is to provide a capable image processing device. [Examples] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram of a document reading device to which the present invention is applicable. It consists of several thousand light receiving elements in order to read the image information of the original 102 held by the original cover 110 and placed on the original table 101.
An image sensor 103 such as a CCD line sensor is used, and illumination light from a light source 104 is reflected on the surface of the original 102, and an image is formed on the image sensor 103 by a lens 108 via mirrors 105, 106, and 107. . Light source 104, mirror 105 and mirror 1
06 and 107 are adapted to move at a relative speed of 2:1. This light source 104 and mirror 10
The optical unit consisting of 5,106,107 is DC
It moves back and forth at a constant speed under PLL control by a servo motor 109. The moving speed is 90mm/90mm on the outward path from left to right depending on the reading magnification.
sec to 360mm/sec, and always 630mm/sec on the return journey from right to left. The direction in which this optical unit moves is called the sub-scanning direction, and the optical unit is moved forward from the left end to the right end while reading the main scanning line perpendicular to this sub-scanning direction with a resolution of 16 pel/mm (main scanning). After that, it is moved back to the left end again to complete one scan. Through the above operations, the entire surface of the document 102 placed on the document table 101 is sequentially read line by line, and the image sensor 103 repeatedly outputs an analog image signal indicating the density of the read image for each line. . FIG. 2 shows a schematic block diagram of a circuit that processes analog image signals from the image sensor 103. The image signal V _D read by the image sensor 103 is converted by the A/D converter 201 into a 6-bit digital signal digitally indicating the image density of each pixel. A/
The digital signal output of the D converter 201 is sent to the latch 20 in synchronization with the sampling clock SCL which is synchronized with the image data clock CLK for reading out the image signal from the image sensor 103 via the latch 202.
3. Comparators 204, 207, latch 20
5,208 in 6-bit parallel. Comparator 204 compares the 6-bit image signal sent from latch 202 with the 6-bit image signal sent from latches 203 and 205, and if the new image signal sent from latch 202 is better. If it is smaller, a comparison output is output to the AND gate 206. AND gate 206 synchronizes the comparator output from comparator 204 with sampling clock SCL to latch 20.
Send to 5. Similar to the comparator 204, the comparator 207 compares the 6-bit image signal sent from the latch 202 with the 6-bit image signal sent from the latches 203 and 208.
If the new image signal sent from 2 is larger, a comparator output is output to AND gate 209. AND gate 209 uses the comparator output from comparator 207 as a sampling clock.
SCL is synchronized and sent to latch 208. The latches 205 and 208 are the AND gates 20 and 20, respectively.
Upon receiving the comparator output from the latch 209, the 6-bit image signal sent from the latch 202 is latched and sent to the CPU 211. As a result, the minimum and maximum values of the image signals inputted up to that point are latched in the latches 205 and 207, respectively. In addition to the comparator output and sampling clock SCL, the AND gates 206 and 209 have
An enable signal EN indicating the valid section of each line of the image signal from the image sensor 103 is input. Therefore, the comparison results for the image signals in a predetermined section for each main scanning line are output from the latches 205 and 208.
It is configured to be sent to CPU211. The CPU 211, which consists of a microcomputer,
By capturing the image signals from the latches 205 and 208 in synchronization with the synchronization signal MS for each main scanning line, the lowest density level (hereinafter referred to as white peak) and the highest density level (hereinafter referred to as white peak) of each main scanning line is captured. black peak) can be detected. The CPU 211 determines a slice level based on the white peak and black peak detected for each line using an algorithm described later in accordance with a program stored in the ROM 212 in advance, and sends the slice level to the comparator 210. The comparator 210 compares the 6-bit image signal from the latch 203 with the 6-bit slice level from the CPU 211, and generates a binary signal (image data VIDEO) indicating white/black for each pixel. Note that the coordinate detection unit 215 detects the coordinates (position) on the document table 101 of the document placed on the document table 101 of the document reading device. Also,
214 is an operation display section provided on the top surface of the document reading device shown in the first diagram; 213 is a memory RAM that temporarily stores calculation data of the CPU 211; Figure 3 shows the document table 10 of the document reading device (Figure 1).
1 shows a state in which a document is placed on top. In this case, the coordinates of four points from the reference coordinate SP on the document table 101, where X is the main scanning direction and Y is the subscanning direction, are the coordinates X ₁ ,
Y ₁ , X ₂ , Y ₂ , X ₃ , Y ₃ , X ₄ , and Y ₄ are detected by pre-scanning the optical system. The document cover 110 (FIG. 1) is mirror-finished so that image data outside the area where the document is placed is always black data. The pre-scanning includes main scanning and sub-scanning to cover the entire glass surface. FIG. 4 shows a detailed circuit configuration of the coordinate detection section 215. In the figure, a main scanning counter 351 is a down counter and represents a scanning position in one main scanning line. This counter uses the horizontal synchronization signal HSYNC
The countdown is performed each time the image data clock CLK, which is set to the maximum value in the main scanning direction (X direction), is input. The sub-scanning counter 352 is an up counter that is reset to "0" at the rising edge of VSYNC (image leading edge signal), counts up in response to the HSYNC signal, and represents the scanning position in the sub-scanning direction. During pre-scanning, the image data VIDEO binarized by the comparator 210 is input to the shift register 301 in units of 8 bits. Note that during pre-scanning, the CPU 211 supplies a predetermined fixed slice level to the comparator 210. When the 8-bit input is completed, the gate circuit 302 checks that all of the 8-bit data in the shift register 310 is a white image (0 level), and outputs 1 to the signal line 303 if all of the 8-bit data is a white image. After the start of pre-scanning of the original, an F/F (flip-flop) 304 is set when the first 8-bit white appears. This F/F 304 is reset in advance by VSYNC (image leading edge signal output at the start of forward movement). After that, it remains set until the next VSYNC. The main scanning counter 351 counts down by a clock synchronized with each pixel output of the image data from the comparator 210, and when the F/F 304 is set, the value of the main scanning counter 351 at that time is loaded into the latch 305. . This becomes the X ₁ coordinate value. The sub-scanning counter 352 counts up the signal synchronized with the scanning of each line, and the latch 306
The value (number of lines) of the sub-scanning counter 352 when the F/F 304 is set is loaded. This is
Y becomes ₁ coordinate value. Therefore, P ₁ , X ₁ , and Y ₁ are found. Also, each time 1 is output to the signal 303, the value from the main scanning counter 351 is loaded into the latch 307. When the value from main scan counter 351 when the first 8-bit white appears is loaded into latch 307, latch 310 (which is
The comparator 309 compares the magnitude with the data of the direction (which is set to the maximum value of the direction). Moshi Latch 307
If the data in latch 307 is smaller, the data in latch 307 is loaded into latch 310. Also, at this time, the value of the sub-scanning counter 352 is loaded into the latch 311. This operation is processed until the next 8 bits enter shift register 301. Latch 3 like this
07 and the latch 310 for the entire image area, the minimum value of the document area in the X direction remains in the latch 310, and the coordinate in the Y direction at this time remains in the latch 311. That is, since the main scanning counter 351 is a down counter, the coordinate corresponding to the minimum value in the X direction represents the coordinate closest to SP in the main scanning direction. These are the P ₂ , X ₂ , Y ₂ coordinates. The F/F 312 is an F/F that is set when 8-bit white appears for the first time in each main scanning line, and is reset by the horizontal synchronizing signal HSYNC, set at the first 8-bit white, and held until the next HSYNC. When the F/F 312 is set, the value of the main scanning counter 351 corresponding to the position of the first white signal appearing in one line is set in the latch 313. The value of the latch 315 and the comparator 316 are then compared in magnitude. The latch 315 is preset to the minimum value in the X direction, ie, 0, at the time VSYNC occurs. If the data of latch 315 is better than latch 31,
If the data is less than or equal to 3, the signal 317
becomes active and the data in latch 313 is loaded into latch 315. This operation is HSYNC−
This is done between HSYNCs. When the above comparison operation is performed for the entire image area, the maximum value of the document coordinates in the X direction, that is, the X coordinate of the white signal from the point farthest from the scanning start point in the main scanning direction remains in the latch 315. Become. This is _X3 . Also, when signal line 317 outputs, the value from sub-scan is loaded into latch 318. This becomes Y ₃ , P ₃ ,
X ₃ and Y ₃ are obtained. Latches 319 and 320 are 8 in the full image area.
Each time a bit white appears, the value of the main scanning counter and the value of the sub-scanning counter at that time are loaded. Therefore, when the document pre-scanning is completed, the count value at the time when 8-bit white appears last remains on the counter. These are P ₄ , X ₄ , and Y ₄ . The above eight latches 306, 311, 320,
The data lines 318, 305, 310, 315, and 319 are connected to the bus line BUS of the CPU 211, and the CPU 211 reads this data at the end of the forward movement in the previous scan. FIG. 5 shows a flowchart of the document reading sequence. Note that steps 501 to 507 relate to pre-scanning. First, in step 501, the optical unit performs forward scanning from the left end to the right end in FIG.
15 detects the coordinates of the document on the document table 101, and captures each detected coordinate data. Next, in step 502, the area in which the peak value for determining the slice level for binarization should be sampled is calculated from the coordinate data detected in step 501. For example, from the coordinates detected for a document placed as shown in the shaded area in FIG. 3, Y ₃ ,
Select a rectangular area surrounded by Y ₂ , X ₁ and X ₄ . This is because the original is normally placed as parallel to the original table as possible, and even if the original is placed at a slight angle as shown in Figure 3, unnecessary information outside the original will not be mistaken as data from the original. This is because there is no danger of it being stolen. Of course, the sampling area may be determined using other methods. As can be seen from FIG. 6, when the document coordinate detection is completed, the optical system is at a point in the sub-scanning direction Ymax. At this point, the peak value sampling start point Y ₂ and end point
Since Y ₃ is known, step 504 in Figure 5 and
You can set a schedule to execute 505 and 506. That is, when the backward movement is started in step 503, the CPU 211 counts the main scanning line synchronization signals for the distance (Ymax - _Y2 ), and then starts detecting the white peak value/black peak value described above in FIG. ,
Furthermore, after counting the main scanning line synchronization signals for a distance equivalent to Y ₂ - Y ₃ from that point, the detection of the peak value is completed, and after counting the main scanning line synchronization signals for a distance equivalent to Y ₃ , the stop moving. It goes without saying that when peak value detection is started in step 504, the enable signal EN mentioned above is set to be output in correspondence with the detection coordinates X ₁ and X ₄ as shown in FIG. With the above operation, it is possible to reliably detect the white peak and black peak of the image density for each main scanning line in the document placed at any position on the document table 101, and the detection operation can be performed by using something other than the document, such as the document cover. prevent it from being influenced. Next, an algorithm for determining slice levels for binarization will be explained. According to the procedure described above, the CPU 211 takes in the black peak value and the white peak value for each main scanning line from within the document area. Now, if the black peak on the i-th main scanning line is BPi and the white peak is WPi, the image data is a 6-bit value, so they are respectively 0\0\ _(HEX) to 3F _(HEX).
Takes any value up to and is BPiWPi. The CPU 211 has 64× prepared in the RAM 213.
2-byte black peak histogram area and 64×
2 in the 2-byte white peak histogram area
Among the contents of byte areas HB(j) and HW(j), the areas corresponding to the detected data BPi and WPi are counted up one by one. Then, it waits for the next main scanning line synchronization signal MS, takes in the data BPi+ ₁ and WPi+ ₁ from the i+1th line, counts up the corresponding area of the histogram again, and continues until the end of the sample in step 505. However, at this time, the detected BPi and WPi are not necessarily used as histogram data. For example, if there is a band of uniform density in the main scanning line direction, the sample values BPi and WPi from that band will be almost equal, even if it is pure white, pure black, or other density, and the background part and the information part will be distinguished. Separately 2
It is not suitable as information for valuing. Further, since the density is not necessarily uniform even in the background area, appropriate binarization cannot be performed even if the black peak of the variation in the background level is treated as the information level. Therefore, when the CPU 211 determines that BPi−WPiα, that is, the difference between the black peak value and the white peak value is smaller than a predetermined value and there is little change in density, the CPU 211 uses the BPi and WPi as data for creating a histogram. do not. This α is a constant set empirically. On the other hand, there may also be cases where a value whiter than the actual background level due to dust on the platen glass is sampled as a white peak, or a value blacker than the actual information level due to dirt etc. is sampled as a black peak. These cases are also not suitable as data for creating a histogram. Therefore,
When the CPU 211 is BPiβ or WPiγ, that is,
If the black peak value or white peak value is a unique value that deviates from the respective reference value, its BPi, WPi
is not used as data for creating histograms. These β and γ are also constants set empirically. Also, before starting sampling in step 504, the entire histogram area of RAM 213 is 64×2.
It is natural to clear the x2 byte to 0\. FIG. 7 shows a detailed flowchart of peak value sampling in steps S504, 505, and 506 in FIG. 5, and will be described below. First, the CPU 211 clears the histogram creation areas HW(j) and HB(j) to 0\(S14
-1). These HW(j) and HB(j) are shown in RAM21 in Figure 2.
In the area above 3, both HW(j) and HB(j) are composed of 2 bytes for each j, and j is the possible value of the detected peak value from 0\(00 _HEX ) to 63(3F _HEX )
Therefore, HW(j), j=0, . . . , 63, totals 2×64=128 bytes, and HB(j) also has a total of 128 bytes. HW(j) is the white peak value WPi (=
Indicates the frequency of j). HB(j) is the black peak BPi(=j)
shows the frequency of 2 areas for creating histograms each
If there are bytes, it can be counted up to 65,535, and with a resolution of 16 pels, the total number of main scanning lines for A3 is 6,720 lines, which is sufficient. Next, the CPU 211 initializes the main scanning line number i (S14-2), and when detecting the end of the peak value detection of the first line using the main scanning line synchronization signal MS (S14-3), the CPU 211 initializes the main scanning line number i from the latch described above. The white peak value WP ₁ and the black peak value BP ₁ are taken in (S14-4). If BP ₁ −WP ₀ ≦α, that is, the difference between each peak is smaller than the predetermined value α, BP ₁ and WP ₁ are not used as histogram data as described above (S14-5). On the other hand, if BP ₁ -WP ₁ >α, then it is determined whether BP ₁ ≧β, that is, the black peak value is larger than the predetermined value β, and if it is larger, it is not used as the histogram creation data (S14-6). If BP ₁ <β, then it is determined whether WP ₁ ≦γ, that is, the white peak value is smaller than the predetermined value γ, and if it is smaller, it is not used as histogram creation data (S14-7). If WP ₁ > γ, WP ₁ and BP ₁ are used as histogram creation data, and the white peak value is
Frequency area HW on RAM corresponding to WP ₁ (WP ₁ )
is increased by 1 count (S14-8), and the black peak value is
A similar HB (BP ₁ ) corresponding to BP ₁ is counted up by 1 (S14-9). After peak value sampling and histogram generation or data rejection for the first line as described above, the value of i is set to 2, 3, 4...
(S14-10), 2nd, 3rd, 4th, etc.
Similar processing is performed for each line until the backward movement is stopped. As a result, when the sample is completed in step 505 (FIG. 5), histograms as shown in FIGS. 1 and 2, for example, are constructed for each of the black peak BP and white peak WP. After completing the sample, the optical system returns to the starting point and completes the backward movement in step 506. Next, in step 507, the slice level is set. The density level showing the peak of the set frequency of the slice level of each histogram is considered to be each representative value. According to the example in FIG. 8, the density of the document information area is 36H, and the density of the background area of the document is OAH, for example, the median value.
Let 20H be the slice level. Note that there are other ways to determine this slice level, and the operation for determining this slice level will be explained in detail later. Finally, in step 508, the original is read and scanned, and the operation ends. In this case, step 507
It goes without saying that the slice level CPC 211 determined in step 1 is supplied to the comparator 210. Black peak BP for values that are blacker than the actual information level
A case in which sampling is performed will be explained using FIG. 9. OG of images with dirt GD etc. on the platen glass
When the peak value is sampled from , the dirty portion GD is extremely black, resulting in a black peak value BP, and the white peak WP and black peak BP are sampled as shown below. If this is used as histogram generation data as is, the maximum value of the black peak histogram will be higher in the dirty part than in the information part, so the slice level will be determined to be higher than the density of the information part, and appropriate binarization will be performed. Not done. In this case, if we adopt the value β mentioned above and discard the black peak value BP of the dirty area as the histogram generation data, the black peak histogram in that case has the maximum value at the density value of the information area and is appropriate. The desired slice level can be determined. Similarly, regarding the case where a value whiter than the actual background level is sampled as the white peak WP,
This will be explained using FIG. 9. When reading a rough original with dust on the platen glass, the dusty part DS is extremely white and is sampled as the white peak value WP. If this data is used as is to generate a histogram, the slice level will be determined to be whiter than the actual background, and appropriate binarization will not be performed. In such a case, if we do not adopt the value of γ mentioned above and use the white peak value WP of the dusty area as the histogram generation data, a mountain in the white peak histogram will be generated in the actual background area, as shown below.
An appropriate slicing level is determined. Therefore, by combining the black peak value BP and white peak value WP correction operations using the values of β and γ as described above, it is possible to determine a good slice level that is not affected by noise or the like. Alternatively, a parameter may be set for either the white peak value or the black peak value, and if either peak value is greater than or equal to the parameter or less than that parameter, that value may be invalidated as data for creating a histogram. FIG. 10 shows an operation display section 214 provided on the top surface of the document reading device for density selection. 802
is a density display section made up of seven LEDs that can indicate seven levels, and shows that density 4 is selected. Each time the key 800 is pressed, the display stage 802 moves one step to the left, and each time the key 801 is pressed, the display stage 802 moves one step to the right. Reference numeral 803 is a key for selecting the contrast of the original, and each time this key is pressed, the display of the three LEDs 804 changes in stages from normal to high contrast to low contrast to normal. The operating status of each key on this operation display section 214 is
The information is taken in by the CPU 211, and display units such as LEDs perform display operations in accordance with commands from the CPU 211. The concentration display stage of the LED 802 is f(=1,...,
7), and the slice level for binarization is set as Wpp, the density level of the background part of the document estimated from the white peak histogram, and Bpp, the density level of the document information part estimated from the black peak histogram.
S _L can also be determined as S _L =Bpp+Wpp/2+[Bpp-Wpp/8]×(f-4). However, [ ] is a Gaussian symbol. For example, in the case of Figure 8 mentioned above, Wpp=
Since φA _H , Bpp=36 _H , the relationship between density display and slice level is as shown in the following table.

[Table] FIG. 11A is a graph showing the relationship between the histogram shown in this table and the slice level. In this way, by changing the internal division ratio of the slice level, which is created by internally dividing the area between the background level estimated by peak value detection and the information level, using the density display f, it is possible to perform operations while completely removing the background. It is possible to make adjustments such as making the intermediate density part darker or lighter depending on the user's preference. For example, in a case where there is a second maximum value such as point Bp ₂ in the black peak histogram as shown in Figure 11A, the reading device needs to check whether the level indicating Bp ₂ is an information level or a background level. cannot be determined. Therefore, the operator can use the keys 800 and 801 to select f5 or higher to set _Bp2 as the background level, or select f4 or lower to set Bp2 as the information level. Furthermore, the above method also has the advantage of increasing the resolution of the concentration display f. For example, as shown in Figure 11C, the slice level corresponding to the density display f is

[Table] If the image is fixed as shown in FIG. Furthermore, in this case, f6 is located in a mountain of black peaks, and part of the information part is cut off, while f2 is located in a mountain of white peaks, and the background is covered. Therefore,
In reality, only three stages, f3 to f5, can be expressed. However, if the slice level is determined between the estimated background level and black level in accordance with the density display f as shown in FIG. 11A, it becomes possible to express the image in seven levels, which is effective. The above is a case of one slice level, that is, binary image output, but two slice levels,
That is, in the case of outputting a ternary value image, two types of slice levels can be similarly set between the background and information levels estimated by peak detection, corresponding to the density display f, as shown in FIG. 11B. FIG. 12 shows a flowchart for calculating the slice level, and will be described below. After completing the peak value sampling as described above, in each of the generated histograms of the black peak and white peak, Wpp such that HW(Wpp) = maxHW(j), that is,
The concentration level Wpp that shows the highest frequency in the white peak histogram and HB (Bpp) = maxHB (j)
Bpp, that is, the density level Bpp that shows the highest frequency in the black peak histogram (S15
-1, S15-2). After that, the slice level determination step (S15-
10) Determine the slice level. As the slice level determination step (S15-10), one of four algorithms A, B, C, and D is executed. A desired slice level can be obtained by selecting one of these four algorithms using a mode key (not shown) provided on the operation display section 214. Note that it is not necessary to provide all four algorithms, but it is sufficient to provide at least one. Algorithm A is an example in which the average value of Wpp and Bpp mentioned above is used as the slice level S _L for a binary image (S15-3). Algorithm B uses the concentration display step value f described above using FIG.
This is an example in which the slice level S _L is determined by changing the internal division ratio of and Bpp (S15-4, 5). Algorithm C is an example of determining two slice levels S _{L A} and S _{L B} for reading a ternary image.
S _{L A} and S _{L B} internally divide Wpp and Bpp at a ratio of 1:1:1 (S15-6). The example in Figure 8 above (Wpp=
OA _H , Bpp = 36 _H ), S _{L A} = 27 _H , S _{L B} =
_19H . Algorithm D is the concentration display stage value f
This is an example of determining two slice levels S _{L A} and S _{L B} for three images by changing the internal division ratio of Bpp and Wpp, and the calculation formula is as follows: S _{L A} = Wpp + 2Bpp/ 3+Bpp−Wpp+2Bpp/3/
4×(f-4) [at f4] =Wpp+2Bpp/3+Wpp+2Bpp/3-Wpp/4
×(f-4) [When f<4] S _{L B} =2Wpp+Bpp/3+Bpp-2Wpp+Bpp/3/
4×(f-4) [at f4] =2Wpp+Bpp/3+2Wpp+Bpp/3-Wpp/4
×(f-4) [When f<4] According to the above equation, the relationship between slice level SL and f is as shown in the table below.

〔effect〕

As explained above, according to the present invention, the maximum and minimum values of the image density level of the original are detected for each line, and the image signal obtained by reading the original is processed based on the detected maximum and minimum values. At the same time,
If the difference between the detected maximum and minimum values is not within a predetermined range, the maximum and minimum values for that line are invalidated, making it ideal for originals that include solid white, solid black, or halftones. This makes it possible to perform sophisticated image processing.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a document reading device to which the present invention is applied, Fig. 2 is a block diagram of an image signal processing circuit, and Fig. 3 is a block diagram of an image signal processing circuit.
The figure shows the coordinates of the document on the document table, FIG. 4 is a block diagram of the coordinate detection unit, FIG. 5 is a flowchart showing the document reading sequence, and FIG. 6 shows the document placement position and the document reading sequence. Diagram showing correspondence,
Figure 7 is a flowchart showing the peak value sampling procedure, Figures 8 1 and 2 are diagrams showing examples of black peak histograms and white peak histograms, respectively, and Figures 9 and 14 are slice level determination for various originals. Figure 10 is an external view of the operation display section, Figures 11A, B, and C are diagrams showing the relationship between peak values and slice levels, and Figure 12 is a flowchart showing the procedure for calculating slice levels. Fig. 13 is a diagram showing the setting operation of parameter α, Fig. 1
FIG. 5 is a diagram showing the setting operation of parameters α and γ, and FIG. 16 is a diagram showing another procedure for peak value sampling.
202, 203, 205, 207 are latches, 20
4,207 is a comparator, 211 is a CPU, 2
15 is a coordinate detection circuit, and 214 is an operation display section.

Claims (1)

[Claims] 1. means for reading an original image; means for detecting the maximum and minimum values of the image density level of the original image for each line; means for processing the image signal from the reading means based on the detection means, and if the difference between the maximum value and the minimum value detected by the detection means is not within a predetermined range, the maximum value and minimum value of that line are invalidated. An image processing device characterized by: 2. An image processing device according to claim 1, characterized in that a reference range for invalidating the maximum value and minimum value detected by the detection means is variable. 3. The image processing device according to claim 1, wherein the processing means quantizes the image signal from the reading means.