JPH084311B2 - 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 an image in which the density of a document image placed on a document table is faithfully determined and an image signal is converted into a reproduction signal based on the determination result. Regarding a processing device.

2. Description of the Related Art Conventionally, the density of an image in a document is detected, and various image processes are performed based on the result, for example, a read image signal is detected.
An image processing device for digitizing is known.

However, conventionally, since the original is always placed at a predetermined position on the original plate, the image signal of a predetermined area is extracted, so that the original is placed at a predetermined position on the original plate. If not, there is a risk that the density of the original image may be determined based on unnecessary density information other than the original area on the original table.

Further, this has a drawback that the density of a wide range of the original image cannot be accurately detected, and a reproduction signal faithful to the original information cannot be obtained.

The present invention has been made in view of the above-described prior art, and an object thereof is to detect a wide range of density within a document area with high accuracy and at high speed, thereby producing a reproduction signal faithful to document information. An image processing device that can be obtained at high speed is provided.

Embodiments Embodiments 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 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 servo motor 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 reading 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 back to the left end again. Finish scanning.
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 that processes 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 passed through the latch 202.
Latch 203, comparators 204 and 207, latch 205 in synchronization with
・ Sent to 208.

The comparator 204 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 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.

In the comparator 207, the 6-bit image signal sent from the latch 202 is compared with the 6-bit image signal one clock before sent from the latch 203, and the new image signal sent from the latch 202 is compared. 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.

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 display 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. The CPU 211 takes in the image signals from the latches 205 and 208 in synchronization with the main scanning line synchronization signal MS, so that 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.

CPU211 determines the slice level by the algorithm described later based on the white peak and black peak detected for each line,
Send to the comparator 210. Latch 20 for comparator 210
The image signal from 3 and the slice level from the CPU 211 are compared to generate a binarized signal VIDEO. A binary output data ROM is provided in place of the comparator 210, and the ROM pattern is selected by the CPU 211 based on the recognition, and the pattern is latched.
It is also possible to address by the data from 3 and output the corresponding binary data. In this case, it is possible to reproduce the halftone in binary with the ROM storing the dither pattern.

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, the coordinates of four points (X ₁ , Y ₁ ), (X ₂ , Y ₂ ), (X ₃ ,, where X is the main scanning direction and Y is the sub scanning direction from the reference coordinates SP on the document table 101 Y ₃ ), (X ₄ , Y ₄ ) is detected by pre-scanning the optical system. Make sure that the original cover 110 is set so that the image data outside the area where the original is placed is always black.
(Fig. 1) is mirror-finished. 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 8-bit units. When the 8-bit input is completed, the gate circuit 302 checks whether all the 8-bit data are black and white images, and if Yes, outputs 1 to the signal line 303. F / F304 is set when the first 8-bit white appears after scanning the original. This F / F is VSYNC
(Image leading edge signal) is preset. After that, it is set and released until the next VSYNC comes. F / F304
When is set, the latch F / F 305 is loaded with the value of the main scanning counter 351 at that time. This becomes the X ₁ coordinate value.
The value of the sub-scanning counter 350 at that time is loaded into the latch 306. This is the Y ₁ coordinate value. Therefore, P ₁ (X ₁ , Y ₁ ) can be obtained.

The value from the main scan is loaded into the latch 307 every time 1 is output to the signal 303. 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-bit white appears is loaded into the latch 308, the data in the latch 310 (which is set to “0” at the time of VSYNC) is compared in magnitude with the comparator 309. It If the data in the latch 308 is larger, the data in the latch 308, that is, the data in 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. When the data of the latch 308 and the latch 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 coordinate in the Y direction at this time remains in the latch 311. This is the P ₂ (X ₂ , Y ₂ ) coordinate.

The F / F 312 is an F / F that is set when the first 8-bit white appears for each scanning line, is reset by the horizontal synchronizing signal HSYNC, is set by the first 8-bit white, and is held until the next HSYNC. At the time when this F / F312 is set, the value of the main scan counter is set in the latch 313, and the latch 31 is set until the next HSYNC.
Load to 4. Then, the size of the latch 315 and that of the comparator 316 are compared. The maximum value in the X direction is reset in the latch 315 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, when the signal line 317 outputs, the value from the sub-scan is loaded into the 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 above eight latches (306,311,320,318,305,310,315,
The data line 319) is connected to the bus line BUS of the CPU in FIG. 2, and the CPU will read this data at the end of the prescan.

FIG. 5 is a flowchart of the document reading sequence.
Fig. 2 The program is stored in ROM and implemented 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 Y 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 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 Y ₂ and the end point Y ₃ are known. You can schedule 505 and 506 to run. That is, when the backward movement is started in step 503, the CPU 211 counts the main scanning line synchronizing signals by the distance (Ymax-Y ₂ ) and then starts the above-mentioned white peak value / black peak value detection. After the main scanning line synchronization signal is counted by the distance (Y ₂ -Y ₃ ), the peak value detection is ended, and the main scanning line synchronization signal is counted by the distance Y ₃ 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 shown in FIG.
Set in correspondence with X ₁ and X ₄ .

With the above operation, it is possible to detect the white peak and the black peak 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.

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.
Takes any value from O (HEX) to 3F (HEX) and B
Pi ≧ WPi.

The CPU has 1 each of the contents of the 2-byte area corresponding to the detected data BPi and WPi in the 64 × 2-byte black peak histogram area and 64 × 2-byte white peak histogram area prepared in RAM. Count up,
Wait for the next main scanning line synchronization signal MS, take in the data BPi + 1 and WPi + 1 from the (i + 1) th line, count up the corresponding area of the histogram again, and perform the following steps.
Continue until the end of the 505 sample.

However, at this time, the detected BPi and WPi are not always used as the histogram data.

For example, if there is a uniform density band in the main scan line direction, whether it is pure white or pure black, and at other densities, the sample values BPi and WPi from there will be almost the same, and the background and information will be displayed. It is not suitable as information for binarization that requires data to be distinguished. Therefore, when BPi−WPi ≦ α, the CPU discards BPi and WPi without using them as histogram data, and waits for BPi + 1 and WPi + 1. This α is a constant that is set empirically and is, for example, 4 or 3. In addition, it is natural that the entire histogram area 64 × 2 × 2 bytes is cleared to 0 before the sampling is started in step 504.

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.

According to the example of FIG. 7, the density of the document information portion is 36H, the density of the background portion of the document is OAH, and the median value 2OH is the slice level.

As a method of determining the slice level, it is also possible to determine 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.

Finally, in step 508, the document reading scan is performed to end the operation.

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 the preliminary scanning 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 is discharged after the reading is completed. In this case, the original 601 can be moved by the belt for setting while the scanning unit 200 is set to the point A beforehand, and the original can be read in the stopped state of 200. The width and length of the document are recognized from the read data at that time. Then, the scanning moving unit is moved back from the point A, and the level of the document is judged. 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, when the binarization based on the recognition is not required, the read data of the document moving at the point A with the scanning unit stopped is binarized and output as it is to read. The time required can be shortened.

Effect As described above, according to the present invention, an area for detecting the original density is set in the original area, the peak value of the image signal in line units is detected for a plurality of lines in the area, and after the detection is completed. , The density of the original is determined based on the peak value from the entire area, and the density of the original can be accurately detected by referring to a wide range of the original. Further, when the reading means for reading the original document is moved forward, an area for recognizing the original document on the document table is set, and an area for detecting the original density is set. Since the value is detected, the original density in the original area can be determined at high speed.

Therefore, a reproduction signal faithful to the document information can be obtained at high speed.

[Brief description of drawings]

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. 4 is position coordinates. 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)

[Claims] 1. A reading means for reading an original and outputting an image signal, a scanning means for reciprocally scanning the reading means to scan the entire surface of the original, and a forward movement of the reading means by the scanning means. In order to detect the document density in the area where the document exists based on the recognition result of the recognition means and the recognition means that recognizes the area where the document exists on the platen on the basis of the image signal from the reading means when moving. Setting means for setting the area of the line, and when the scanning means returns to the reading means, the peak value of each line is set to a plurality of lines based on the image signal from the reading means within the area set by the setting means. Based on the detecting means for detecting and the plurality of peak values from the entire area of the area detected by the detecting means after the returning of the reading means by the scanning means is completed. A processing means for judging the density of the original, moving the reading means forward by the scanning means again, and converting the image signal obtained from the reading means during the forward movement into a reproduction signal based on the judged original density; An image processing apparatus comprising: