JP2541937B2 - Image processing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more particularly, to forming a histogram of the maximum value and the minimum value of each line in a document area and performing gradation correction of an image signal based on the histogram. The present invention relates to an image processing device that selects a gamma conversion characteristic for

(Description of Prior Art) Conventionally, there is known an image processing apparatus that detects the density of an image in a document and performs various image processing on an image signal obtained by reading the document based on the result. .

For example, in Japanese Laid-Open Patent Publication No. 53-30216, the number of input image signals is 2 based on the maximum value and the minimum value of the image signals in one line.
Forming a value reproduction signal is disclosed. However, in this case, since the input image signal is processed based on the image information of one line, there is a drawback that the density of a wide range of the original image cannot be detected accurately.

(Object) The present invention has been made in view of the above-described conventional technique, and an object of the present invention is to detect a wide range of densities in a document area, and moreover, it is possible to accurately detect an information part and a background part in the document,
This provides an image processing device capable of selecting an optimum gamma conversion characteristic for gradation conversion of an image signal.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a document reading apparatus 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 the document 102 placed on the document table 101 and held by the document cover 110.
The light is reflected on the surface 102 and is imaged on the image sensor 103 by the lens 108 via the mirrors 105, 106 and 107. The light source 104, the mirror 105, and the mirrors 106, 107 move at a relative speed of 2: 1. This optical unit is a DC servomotor 109
Moves from left to right at a constant speed while applying PLL control by. This moving speed is 90 mm / sec depending on the magnification in the outward path
To 360 mm / sec, and always 630 mm / sec on the return trip
Is. While scanning the main scanning line orthogonal to the moving sub-scanning direction A of this optical unit with the image sensor at a resolution of 16 pel / mm, the optical unit is moved forward from the left end to the right end, and then moved to the left end again. Finish the scan.
It is also possible to read the original while moving it, and thus the total time required for reading can be shortened.

FIG. 2 shows a schematic block diagram of a circuit for processing an image signal from the image sensor 103. The image signal V _D read by the image sensor 103 is converted into a 6-bit digital signal by the A / D converter 201, and the sampling clock SCL is supplied via the latch 202.
Latch 203, comparators 204 and 207, latch 205 in synchronization with
・ Sent to 208.

The comparator 204 compares the image signal of 6 bits sent from the latch 202 with the image signal of 6 bits one clock before sent from the latch 203, and if the new image signal sent from the latch 202 is compared, If is smaller, the comparator output is output to the AND gate 206. The AND gate 206 sends the comparator output from the comparator 204 to the latch 205 in synchronization with the sampling clock SCL.

The comparator 207 compares the 6-bit image signal sent from the latch 202 with the 6-bit image signal one clock before sent from the latch 203, and if the new image signal sent from the latch 202 If is larger, a comparator output is output to the AND gate 209. The AND gate 209 sends the comparator output from the comparator 207 to the latch 208 in synchronization with the sampling clock SCL.

Upon receiving the comparator output, the latches 205 and 208 send the image signal sent from the latch 202 to the CPU 211. Also, the image signal of the latch 205 is sent again to the comparators 204 and 207 and compared with the next signal. If the next image signal is smaller, the latch
202 is changed to that level and the latch 208 retains the previous level.

Further, the AND gates 206 and 209 receive the enable signal EN indicating the effective section of the image signal from the image sensor 103 in addition to the comparator output and the sampling clock SCL, and the comparison result of the image signal in the predetermined section for each main scanning line. Latch 20
It is designed to send from 5,208 to CPU211. CPU211 is
By taking in the image signals from the latches 205 and 208 in synchronization with the main scanning line synchronization signal MS, the lowest density level of the main scanning line from the latch 205 (hereinafter referred to as the white peak) and the highest density level from the latch 206 (hereinafter Black peak). The CPU 211 determines the slice level by an algorithm described later based on the white peak and the black peak detected for each line and sends it to the comparator 210. The comparator 210 compares the image signal from the latch 203 with the slice level from the CPU 211 to generate a binarized signal VIDEO. A binarized output data ROM is provided instead of the comparator 210, and the ROM pattern is read by the CPU2 based on the recognition by the latches 205 and 208.
It is also possible to select by 11 and address the pattern with the data from the latch 203 to output the corresponding binary data. In this case, RO that stores the dither pattern
M makes it possible to reproduce halftones in binary.
The signal VIDEO is stored in a line memory of a printer (not shown), a laser beam or the like can be modulated to obtain a print image, and MODEM modulation can be performed for line transmission.

FIG. 3 shows a state where a document is placed on the document table 101 of the document reading device (FIG. 1). In this case, four coordinates (X ₁ , Y ₁ ), (X ₂ , Y ₂ ), (X ₃ , Y ₃ ), (X ₄ ,
Y ₄ ) is detected by pre-scanning the optical system. The document cover 110 (FIG. 1) is mirror-finished so that the image data outside the area where the document is placed is always black data. In the pre-scanning, main scanning and sub-scanning are performed in order to scan the entire glass surface.

The circuit diagram of FIG. 4 shows the logic for detecting the coordinates. The image data VIDEO binarized by the pre-scan is input to the shift register 301 in units of 8 bits. When 8-bit input is completed, the gate circuit 302 checks whether all 8-bit data are white images, and if Yes, outputs 1 to the signal line 303. The F / F 304 is set when the first 8-bit white appears after scanning the original. This F / F is VSYNC
It is reset in advance by (generated by detecting the position where the scanning of the original starts with the image leading edge signal). After that, the next
It is set and released until VSYNC comes. When the F / F304 is set, the latch F / F305 is set to the main scan counter 351 at that time.
The value of (counting down the sample clock and resetting with HSYNC) is loaded. This becomes the X ₁ coordinate value. Further, the latch 306 is loaded with the value of the sub-scanning counter 350 at that time. This is the Y ₁ coordinate value. Therefore P ₁ (X ₁ ,
Y ₁ ) is obtained.

Whenever 1 is output to the signal 303, the latch 307 is loaded with the value from the main scan. This value is immediately stored in latch 308 until the next 8 bits enter shift register 301.
When the value from the main scan when the first 8 bits of white appears is loaded into the latch 308, the data of the latch 310 (which is set to "0" at the time of VSYNC) is compared with the comparator 309. It If the data of the latch 308 is larger, the data of the latch 308, that is, the data of the latch 307 is loaded into the latch 310. At this time, the value of the sub-scanning counter is loaded in the latch 311. This operation is processed until the next 8 bits enter the shift register 301. If the data of the latches 308 and 310 is thus obtained for the entire image area, the maximum value in the X direction of the original area remains in the latch 310, and the coordinates in the Y direction at this time remain in the latch 311. This is the P ₂ (X ₂ , Y ₂ ) coordinate.

The F / F312 is a horizontal sync signal HSYNC (original 1) which is a F / F which is set at the time when 8 bit white first appears for each main scanning line.
It is reset at each line scan) and is set at the first 8 bit white, and is 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 loaded in the latch 314 until the next HSYNC. Then, the magnitude is compared by the latch 315 and the comparator 316. In the latch 315, the maximum value in the X direction is reset when VSYNC occurs. If the data in latch 315 is greater than the data in latch 314, signal 317 becomes active and latch 314, or the data in latch 313, is loaded into latch 315. This operation is performed between HSYNC and HSYNC. When the above comparison operation is performed on the entire image area, the minimum value of the document coordinates in the X direction remains in the latch 315. This is X ₃ . Also, as signal line 317 outputs, the value from the sub-scan is loaded into latch 318. This becomes Y ₃ .

The latches 319 and 320 are loaded with the values of the main-scanning counter and the sub-scanning counter at each time when 8-bit white appears in the entire image area. Therefore, when the original pre-scanning is completed, the count value at the time when 8-bit white finally appears remains in the counter. This is (X ₄ , Y ₄ ).

The data lines of the above eight latches (6,11,20,18,5,10,15,19) are connected to the bus line BUS of the CPU shown in FIG.
The CPU will read this data at the end of the previous scan.

Figure 5 is a flow chart of the document reading sequence.
Fig. 2 The program is stored in ROM and executed by the CPU.

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

Next, in step 502, the area where the peak value for sampling the slice level for binarization should be sampled,
It is calculated from the coordinate data detected in step 501. For example, from the coordinates detected for an original document such as the shaded area in FIG. ₃ , Y ₃ , Y ₂
And a rectangular area surrounded by X ₁ and X ₄ is selected. This is because the original is normally placed as parallel as possible on the original table, and even if the original is inclined and placed as shown in FIG. 3, there is no possibility of obtaining unnecessary information outside the original. It is also possible to determine the sampling area by another method.

FIG. 6 shows the scanning 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 Y ₂ and end point Y ₃ are known.
You can schedule a schedule to perform 504, 505, and 506. That is, when the forward movement is started in step 503, the CPU 211 counts the main scanning line synchronization signals for the distance (Ymax-Y ₂ ) and then starts the above-mentioned white peak value / black peak value detection. After detecting the main scanning line synchronization signal for the distance (Y ₂ −Y ₃ ), detection of the peak value is terminated, and the main scanning line synchronization signal for the distance Y ₃ is counted, and then the backward movement is stopped. .

When the peak value detection is started in step 504,
The enable signal EN described above is detected as in the sixth detection coordinate.
Set in correspondence with X ₁ and X ₄ .

With the above operation, it is possible to detect the white heak value and the black peak value of the image density for each main scanning line in the document at an arbitrary position on the document table.

Next, an algorithm for determining a slice level for binarization will be described. By the means described above, the CPU 211 takes in the black peak value and the white peak value for each main scanning line from the original area. Then store it in RAM.

Now, assuming that the black peak on the i-th main scanning line is BPi and the white peak is WPi, the image data has 6-bit value, so each takes any value from 00 (HEX) to 3F (HEX),
And BPi ≧ WPi. There is a 64 x 2 byte black peak histogram area and a 64 x 2 byte white peak histogram area prepared in RAM. This stores the frequency number of the peak levels BPi and WPi represented by the 64 gray levels in the area corresponding to each of the 64 gray levels. The CPU counts up the content (frequency) of the 2-byte area corresponding to the detected data BPi and WPi by one, waits for the next main scanning line synchronization signal MS, and waits for the data BPi + 1 from the (i + 1) th line. And WPi + 1 are taken in, the frequency of the corresponding area of the histogram is counted up again, and the following step is performed.
Continue until the end of the 505 sample. However, at this time, detected B
Pi and WPi are not always used as histogram data. For example, if there is a uniform density band in the main scanning line direction, whether it is pure white or pure black, and other density, sample values BPi and WPi
Are almost equal to each other and are not suitable as information for binarization which requires data for distinguishing information from the background. Therefore, when BPi-WPi <α, the CPU discards BPi and WPi without using them as histogram data, and BPi + 1, W
I will wait for Pi + 1. This α is a constant that is set empirically and is, for example, 4 or 3. In addition, the whole histogram area 64 × 2 ×
It is natural to clear 2 bytes to 0.

As a result, when the sampling is completed at step 505, a histogram as shown in FIG. 7 is formed for each of the black peak / white peak. After the sample is finished, the optical system returns to the start point, and when the returning movement is completed at step 506, then the slice level is set at step 507. First, the density level indicating the frequency peak of each histogram is considered as a representative value. This compares the count results of each level of the histogram, and sets the density level having the maximum count result as the maximum frequency level.

According to FIG. 7, the density of the manuscript information part is 36H, the density of the background part of the manuscript is 0AH, and the median value 20H is the slice level. As a method of determining the slice level, the slice level can be determined based on the frequency of another predetermined level of the read data. Further, not only the slice level but also the dither pattern and output pattern stored in the ROM can be selected and determined. Further, the γ conversion characteristic for gradation correction can be selected, or the brightness of the exposure lamp can be simply corrected so that a copy having an appropriate density can be obtained. That is, since it can be seen that there are many intermediate gradations when the black peak and the white peak are in the vicinity of 1F, it is possible to select γ and the like so as to reproduce a high-quality intermediate gradation with less fog.

It should be noted that the simply detected slice level or peak value or the seventh
It is also possible to display the distribution of the figure. Finally step 50
At 8, the document is scanned and the operation ends.

The slice level ROM pattern obtained as described above is retained when the same original is read and copied a plurality of times in succession, and after a predetermined number of copies is completed, the slice level ROM pattern is canceled for a certain period of time. The slice level and the ROM pattern are canceled only when a new original is read, and then a new preliminary scan is performed. The preliminary scanning can be selected as necessary, and the copying speed can be increased without the preliminary scanning.

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

In the case of FIG. 8, if the binarization based on the recognition is not required, the read data of the original moving at the point A with the scanning unit stopped is binarized and output as it is according to a predetermined slice level. As a result, the time required for reading can be shortened.

(Effect) As described above, according to the present invention, the maximum value can be obtained by performing the detection process for detecting the maximum value and the minimum value of the image signal in one line in the original area on a plurality of lines in the original area. And a minimum value histogram is formed, and a gamma conversion characteristic for gradation correction of the image signal is selected based on the histogram, and the density of the document is accurately detected by referring to a wide range of the document. As well as
It is possible to select the optimum gamma conversion characteristic for gradation conversion of the image signal.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a document reading device, FIG. 2 is a block diagram of an image signal processing circuit, FIG. 3 is a diagram showing a relation between a document placed on a document table and position coordinates, and FIG. Detection circuit diagram, FIG. 5 is a flow chart of the image reading sequence, FIG. 6 is a diagram showing the relationship between the document position and the sequence, FIG. 7 is a diagram showing examples of a black peak histogram and a white peak histogram, and FIG. 6 is another schematic view of the document reading apparatus, in which 104 is a lamp, 103 is an image sensor, and 101 is a document table.

Claims (1)

(57) [Claims] 1. A reading means for reading an original and outputting an image signal, a recognizing means for recognizing an area where the original exists based on the image signal from the reading means, and an existence of the original recognized by the recognizing means. Within the area to
Detecting means for detecting the maximum and minimum values of the image signal in the line, and the maximum and minimum values of the image signal in the one line are detected for a plurality of lines in the original area. And a selecting means for selecting a gamma conversion characteristic for gradation conversion of the image signal based on the histogram after the formation of the histogram by the forming means. Image processing device.