JPH0582782B2 - - Google Patents

Description

Detailed Description of the Invention: Technical Field The present invention relates to an image processing device, and in particular, to an image processing device that forms a histogram of maximum and minimum values for each line in a document area, and forms a binary reproduction signal from an image signal based on the histogram. The present invention relates to an image processing device.

Description of the Prior Art Conventionally, an image processing apparatus is known that detects the density of an image within a document and, based on the result, forms a binary reproduction signal from an image signal obtained by reading the document.

For example, JP-A-53-30216 and JP-A-59-
Japanese Patent No. 72856 discloses forming a binary reproduction signal from an input image signal based on the maximum and minimum values of the image signal within one line. However, in this case, since the input image signal is processed based on one line of image information, there is a drawback that it is not possible to accurately detect the density of a wide range of the original image.

Also, for example, the one disclosed in Japanese Patent Application Laid-Open No. 59-72856,
In order to detect the information part and the background part of the original, the maximum and minimum values detected within the line are always used, but if the density within the line of the original is almost equal, the information part of the original described above is used. However, there was a drawback that the background part could not be detected.

Therefore, there was a drawback that it was not possible to obtain a binary reproduction signal faithful to the original information.

Purpose The present invention has been made in view of the above-mentioned prior art, and its purpose is to cover a wide range of densities within the document area,
Furthermore, it is an object of the present invention to provide an image processing device that can accurately detect information portions and background portions within a document, thereby obtaining a binary reproduction signal faithful to the document information.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a document reading device to which the present invention can be applied. A line image sensor 103 such as a CCD is used to read the image information of a document 102 held by a document cover 110 and placed on a document table 101, and illumination light from a light source 104 is reflected on the surface of the document 102. te, mirror 105,10
6, 107, and is imaged onto the image sensor 103 by the lens 108. light source 104, mirror 10
5 and mirrors 106 and 107 are adapted to move at a relative speed of 2:1. This optical unit
It moves from left to right at a constant speed while applying PLL control using the DC servo motor 109. This movement speed varies from 90mm/sec to 360mm/sec depending on the magnification on the outward journey.
Variable up to mm/sec, always 630mm/sec on the return trip.
sec. The main scanning line perpendicular to the sub-scanning direction A in which this optical unit moves is detected by the image sensor.
The optical unit is moved forward from the left end to the right end while reading at a resolution of 16 pel/mm, and then moved back to the left end to complete one scan. Note that it is also possible to read the original while moving it, thereby reducing the total time required for reading.

FIG. 2 shows a schematic block diagram of a circuit that processes image signals from the image sensor 103. Image sensor 10
The image signal V _D read in step 3 is sent to A/D converter 2.
01, it is converted into a 6-bit digital signal and passed through latch 202 to latch 203 and comparators 204 and 20 in synchronization with sampling clock SCL.
7, sent to latches 205 and 208.

The comparator 204 compares the 6-bit image signal sent from the latch 202 with the 6-bit image signal sent from the latch 203 one clock ago, and if the new image signal sent from the latch 202 If is small, AND gate 206
Outputs comparator output to. and gate 206
synchronizes the comparator output from the comparator 204 with the sampling clock SCL and sets the latch 2.
Send to 05.

The comparator 207 compares the 6-bit image signal sent from the latch 202 with the 6-bit image signal sent from the latch 203 one clock ago, and if the new image signal sent from the latch 202 If is large, a comparison output is output to the AND gate 209. The AND gate 209 synchronizes the comparator output from the comparator 207 with the sampling clock SCL.
Send to 8.

When the latches 205 and 208 receive the comparator output, they receive the image signal sent from the latch 202.
Send to CPU211.

Furthermore, in addition to the comparator output and the sampling clock SCL, the AND gates 206 and 209 receive an enable signal EN indicating the valid period of the synchronization signal from the image sensor 103, and perform the comparator of the image signal in a predetermined period for each main scanning line. Latch rate result 205,
208 to the CPU 211.
The CPU 211 takes in the image signals from the latches 205 and 208 in synchronization with the main scanning line synchronization signal MS, thereby obtaining the lowest density level (hereinafter referred to as white peak) and the highest density level (hereinafter referred to as black peak) of each main scanning line. ) 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, and sends it to the comparator 210. A comparator 210 compares the image signal from the latch 203 and the slice level from the CPU 211 to generate a binarized signal VIDEO. Note that a binarized output data ROM is provided in place of the comparator 210, and the ROM pattern is transferred to the CPU 21 based on recognition.
1 and address that pattern with data from latch 203 to output the corresponding binarized data. In this case, the ROM storing the dither pattern makes it possible to reproduce halftones in binary.

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 (X ₁ ,
Y ₁ ), (X ₂ , Y ₂ ), (X ₃ ,, Y ₃ ), and (X ₄ , 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. In order to perform pre-scanning over the entire glass surface, main scanning,
Perform sub-scanning.

The circuit diagram of FIG. 4 shows the logic for detecting the coordinates. Image data binarized by pre-scanning
VIDEO is input to shift register 301 in 8-bit units. When the 8-bit input is completed, the gate circuit 302 checks whether all of the 8-bit data is a white image, and if Yes, outputs 1 to the signal line 303. After starting scanning the original, the F/F 304 is set when the first 8-bit white appears. This F/F is reset in advance by VSYNC (image leading edge signal). From then on, the next
Leave it set until VSYNC comes. F/F
304 is set, the value of the main scanning counter 351 at that time is loaded into the latch F/F 305. This becomes the X ₁ coordinate value. Also, the value of the sub-scanning counter 350 at that time is loaded into the latch 306. This becomes the Y ₁ coordinate value. Therefore P ₁ (X ₁ , Y ₁ )
is found.

Also, each time 1 is output to the signal 303, the value from the main scanning is loaded into the latch 307. This value is immediately stored in latch 308 until the next 8 bits enter shift register 301. The value from the main scan when the first 8 bits of white appear is the latch 308.
When loaded into Latch 310 (this
The comparator 309 compares the data with the data (which is set to "0" at the time of VSYNC). If the data in latch 308 is greater, the data in latch 308, that is, the data in latch 307, is greater than the data in latch 308.
10. Also, at this time, the value of the sub-scanning counter is loaded into the latch 311. This operation is processed until the next 8 bits enter shift register 301. Like this, latch 308 and latch 3
If data No. 10 is applied to the entire image area, the maximum value in the document area X direction remains in the latch 310.
The coordinates in the Y direction at this time remain in the latch 311. This is the P ₂ (X, Y ₂ ) coordinate.

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 is set in the latch 313, and is loaded into the latch 314 until the next HSYNC. Then, the latch 315 and the comparator 316 compare the magnitude.
The latch 315 is set in the X direction at the time of VSYNC occurrence.
The max value has been reset. If Latch 31
If the data in latch 3 is greater than the data in latch 314, signal 317 becomes active and latch 3
14, that is, the data of latch 313 is
5 is loaded. This operation is HSYNC−
This is done between HSYNC. If the above comparison operation is performed for the entire image area, the minimum value of the document coordinates in the X direction remains in the latch 315. This is _X3 . Also, when signal line 317 outputs, the value from sub-scan is loaded into latch 318. This becomes _Y3 .

The latches 319 and 320 are 8
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. This is (X ₄ , Y ₄ ).

The above eight latches 306, 311, 320,
Data lines 318, 305, 310, 315, and 319 are connected to the bus line BUS of the CPU shown in FIG. 2, and the CPU reads this data at the end of the previous scan.

Figure 5 is a flowchart of the document reading sequence, and the program is stored in the ROM in Figure 2.
Executed by CPU.

First, in step 501, the optical system performs forward scanning from the left end to the right end in FIG. 1, and detects the coordinates of the document on the two document tables as described in FIG.

Next, in step 502, an area in which to sample a peak value for determining a slice level for value conversion is calculated from the coordinate data detected in step 501. For example, from the coordinates detected for a document such as the shaded area in Figure 3, the peak value sampling area of this document is Y ₃ , Y ₂ and X ₁ , X _{4 .}
It allows you to select a rectangular area surrounded by . This is because the original is normally placed as parallel as possible on the original table, and even if the original is placed at an angle as shown in FIG. 3, there is no possibility of reading unnecessary information from outside the original. It is also possible to determine the sampling area using other methods. FIG. 6 shows the scanning system path. When the document coordinate detection is completed, the optical system is at the point in the sub-scanning direction Ymax, and the peak value sampling start point _Y2 and end point _Y3 are separated, so step 504 and A schedule for executing steps 505 and 506 can be established. In other words, when the return movement is started in step 503, the CPU
211 counts the main scanning line synchronization signals for the distance (Ymax - Y ₂ ), starts detecting the white peak value/black peak value described above, and then calculates the distance (Y ₂ - Y ₃ ) from that point. After counting the main scanning line synchronizing signal for a corresponding amount, detection of the peak value is finished, and after counting the main scanning line synchronizing signal for a distance corresponding to _Y3 , the backward movement is stopped.

Furthermore, when peak value detection is started in step 504, the enable signal EN mentioned above is set corresponding to the detection coordinates X ₁ and X ₄ as shown in FIG.

With the above operations, the white peak and black peak of the image density can be detected for each main scanning line in the document located at any position on the document table.

Next, an algorithm for determining slice levels for binarization will be explained.

Using the above-described means, the CPU 211 takes in the black peak value and 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 each has a value from 00 (HEX) to 3F (HEX) and BPi ≥ It is WPi.

The CPU stores detected data in a 64 x 2 byte black peak histogram area and a 64 x 2 byte white peak histogram area prepared in RAM.
Count up the contents of the 2-byte areas corresponding to BPi and WPi one by one, have the next main scanning line synchronization signal MS, take in the data BPi+1 and WPi+1 from the i+1st line, and return to the corresponding area of the histogram. count up and continue until the sample ends 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 uniform density band in the main scanning line direction, sample values from that band, whether it is eyelash white or eyelash black, or any other density, can be used.
BPi and WPi are almost the same and are not suitable as information for binarization, which requires data that distinguishes background information from information. Therefore, the CPU
When BPi−WPiα, BPi and WPi are not used as histogram data and are discarded, and BPi+1,
I'll have to wait for WPi+1. This α is a constant set empirically, and is, for example, 4 or 3. Also, it is a matter of course that the entire histogram area 64×2×2 bytes be cleared to 0 before sampling is started in step 504.

As a result, when the sample is completed in step 505, a histogram as shown in FIG. 7, for example, is constructed for each of the black peak and white peak. After completing the sample, the optical system returns to the starting point and completes the return movement in step 506.
Next, in step 507, the slice level is set.

First, the density level showing the peak frequency of each histogram is considered to be the respective representative value.

According to the example in Figure 7, the density of the document information area is 36H,
The density of the background portion of the document is set to 0AH, and its median value, 20H, is set as the slice level, for example.

Note that this slice level can also be determined based on the frequency of another predetermined level of the read data. In addition to the slice level
It is also possible to select and determine dither patterns and output patterns stored in the ROM.

Finally, in step 508, the original is read and scanned, and the operation ends.

The slice level ROM pattern obtained as described above is retained when the same document is read and copied multiple times in succession, and is canceled after a certain period of time after a predetermined number of copies have been completed. Also, only when reading a new document, the slice level and ROM
This cancels the pattern and then performs a preliminary scan. Note that preliminary scanning can be selected as necessary, and it is also possible to increase the copy quality without preliminary scanning.

In FIG. 8, a document 601 is automatically set on the glass 101 by a belt 600 and discharged after reading is completed. In this case, with the scanning unit 200 set in advance at point A, the original 601 is moved with a belt for setting, and the original can be read while the scanner 200 is stopped. The width and length of the document are recognized from the read data at that time. Then, the scanning movement unit is moved back from point A to determine the level of the original. When it is sent to the left end, forward movement is started and binarization is performed based on level recognition of the necessary and effective document area.

In the case of Fig. 8, if binarization based on recognition is not required, the scanned data of the document moving with the scanning unit stopped at point A can be converted into binarized data and output as is. The time required can be shortened.

Effects As explained above, according to the present invention, by performing detection processing for detecting the maximum and minimum values of an image signal within one line within the original area for multiple lines within the original area, the maximum value and the minimum value can be detected. A histogram of the minimum value is formed, and a binary reproduction signal is formed from the image signal based on the histogram. When it is small, the maximum and minimum values are not used as data for the histogram, so it is possible to accurately detect the density of the document by referring to a wide range of the document, and it is also possible to accurately detect the density of the document by referring to a wide range of the document. Detection can be performed with high accuracy, and thereby a binary reproduction signal faithful to the original information can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the document reading device, Figure 2 is a block diagram of the image signal processing circuit, Figure 3 is a diagram showing the relationship between the position coordinates and the document placed on the document table, and Figure 4 is the position coordinates. Detection circuit diagram, Figure 5 is a flow diagram of the image reading sequence, Figure 6 is a diagram showing the relationship between document position and sequence, Figure 7 is a diagram showing an example of a black peak histogram and a white peak histogram, and Figure 8 is a diagram showing an example of a black peak histogram and a white peak histogram. This is another schematic diagram of the document reading device, in which 104 is a lamp, 103 is an image sensor, 10
1 is a document table.

Claims (1)

[Scope of Claims] 1. A reading means for reading a document and outputting an image signal; a recognition means for recognizing an area where the document exists based on the image signal from the reading means; and a document recognized by the recognition means. detecting means for detecting the maximum value and minimum value of an image signal within one line within an area where the image signal exists; forming means for forming a histogram of the maximum value and minimum value; and a binary reproduction signal forming means for forming a binary reproduction signal from the image signal based on the histogram after the formation of the histogram in the formation means is completed. and when the difference between the maximum value and the minimum value of the image signal within the one line detected by the detection means is smaller than a predetermined value, the forming means forms the maximum value and the minimum value. An image processing device characterized in that it is not used as data for a histogram.