JPH07264408A - Image processing unit - Google Patents

Abstract

PURPOSE:To detect the density level of a background area of an original except an original retainer area with high accuracy by identifying a background of the original retainer from that of the original. CONSTITUTION:An object area for detecting a background other than that of a ridge of image data is given by two coordinates and they are set to a register 5. An area discrimination circuit 7 discriminates whether or not a coordinate of a noted picture element in a register 6 is resident within a detection object area and gives the result of discrimination to a background density level detection circuit 7. The background density level detection circuit 7 obtains a minimum density of a picture element in the area and provides an output of it as a background density level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for detecting the background density level of a document with high accuracy.

[0002]

2. Description of the Related Art Generally, in an image processing apparatus such as a copying machine, when a target document is read by an image reading device such as a scanner and the read multi-valued image is output to a printer or a display, the gray level of the background of the document is also reduced. Since it is reproduced as it is, the dirt on the background is not noticeable in the output image. Therefore, conventionally, before outputting an image, a threshold value corresponding to the density level of the background of the document is set, the background is detected based on this threshold, and the stain on the background of the document is removed.

By the way, in a manuscript in which a plurality of manuscripts are pasted together, for example, papers having a high background density such as newspapers and papers having a low background density such as high-quality paper are mixed, and the background density levels have different values. It will be. Therefore, for example, if the background is removed from high-quality paper in accordance with the background density level of newspapers, the highlights and low-contrast characters in the pattern of high-quality paper are removed, or the characters become thin and deteriorate. However, it becomes difficult to read, and conversely, if a threshold value suitable for the background density level of high-quality paper is applied, there is a problem that the background of newspaper is not removed, and a highly accurate threshold value setting method is required.

[0004]

As a conventional threshold value setting method, for example, there is a method described in Japanese Patent Laid-Open No. 4-313744. This method uses the fact that the density level of the background is generally low in the original, and creates a histogram for each specified density area during prescan,
The background density level is automatically detected based on the frequency of the histogram.

However, in the image data read from the image input device such as a copying machine, the original pressing plate is input as the image data signal together with the original. In the threshold setting method described above, there is a problem that the density level of the document press plate is erroneously detected as the background density level when the density level of the document press plate is lower than the background of the document. There is a problem that a considerable amount of processing time is required because a can is required.

As another method, there is a background color detecting method described in Japanese Patent Publication No. 5-23667. In this method, the pressing plate of the original is limited to black in order to detect the leading edge of the original, and when the leading edge is detected, a white level follow-up operation is performed for an area at a certain distance from the leading edge. Therefore, there is a problem that the background density level cannot be detected if the background area of the document does not exist at the leading edge of the document.

It is an object of the present invention to provide an image processing apparatus for discriminating between the document holding plate and the background of the document and detecting the density level of the background region of the document excluding the document holding plate region with high accuracy.

Another object of the present invention is to provide an image processing apparatus which speeds up image processing without performing prescan processing.

[0009]

In order to achieve the above object, the accuracy of automatic threshold setting is improved by designating or automatically detecting the background area of a document and distinguishing between the document retainer plate and the background of the document. It is characterized by The following method is adopted as a method of detecting the background area of a document.
That is, (1) The minimum value of the density of a predetermined area is used as the background removal threshold. (2) The minimum density of the area given by the document size detection is used as the background removal threshold. (3) The minimum value of the density of the area designated by the operator is used as the background removal threshold. (4) The minimum value of the density of the area near the picture character is used as the background removal threshold. Further, another embodiment of the present invention is characterized in that the background density removal processing, the color conversion processing, and the multi-valued processing are speeded up by detecting the background density level without performing the prescan processing. Further, in an image processing apparatus that scans a plurality of times, the background density level is detected during a preceding scan, and given to the background removal section, the color conversion processing section, and the multi-valued processing section during a subsequent scan.

[0010]

In the first embodiment of the background density level detection, the coordinate value representing the detection target area in the image data is preset in the register or the like, and the coordinate value of the pixel of interest is generated in synchronization with the operation of the scanner. It It is determined whether or not the pixel of interest is in the detection target area, the minimum value of the pixel density is obtained for the pixel in the detection target area, and this is set as the background density level. This background density level is set as a background removal threshold, and when the input signal is less than or equal to the background removal threshold, it is determined to be the background and the pixel value is output as 0.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. In order to detect the density level of the background area of a document with high accuracy, if the document holding plate is made of a material equivalent to paper, the white background of the document holding plate and the paper white of the background of the document are Must be identified. In the present invention, the background of the original area excluding the original pressing plate area in the entire image data is designated or automatically identified from the outside, and the background density level of the area is set.

<First Embodiment> FIG. 1 shows the structure of a first embodiment of the present invention. In the figure, a scanner 1 has a photoelectric conversion device such as a CCD sensor, reads an original document (not shown), and outputs three color separation signals of R (red), G (green), and B (blue). CCDs are arranged in a line in the main scanning direction, and CC
The document is read by moving D, a mirror, etc. along the document in the sub-scanning direction. The A / D conversion circuit 2 uses R,
The G and B analog signals are converted into 8-bit digital signals, for example. The shading correction circuit 3 corrects the light distribution of the exposure light source that illuminates the document and the variation of the CCD sensor. The Log (logarithmic) conversion circuit 4 converts the reflectance linear data into density linear data (RGB density signal). For example, when each pixel is converted into an 8-bit digital signal, the RGB density signal of each pixel is 0 to 25.
Takes a value of 5. Therefore, white is (R, G, B) = (0,
0,0), and black is (R, G, B) = (255,25)
5, 255).

When the values of R, G and B are linear reflectance, 255 is the brightest color and 0 is the darkest color.
Further, the reflectance is a ratio (= Ir / Io) of the intensity of the light illuminating the original and the intensity of the light reflected from the original, and the common logarithm of the reflectance is the density (= log (Ir / Io)). ).

In the present embodiment, the data obtained by converting the reflectance signal read by the scanner into the RGB density signal as described above is targeted, but the present invention is not limited to this, and for example, L *. u * b * signal, L * a * b * signal,
It can also be applied to other color systems such as Y (yellow), M (magenta), and C (cyan) signals after color conversion.

Coordinate values representing the detection target area are set in the register 5, and coordinate values of the target pixel are set in the register 6 as needed. The area determination circuit 7 determines whether or not the coordinate value of the pixel of interest is within the detection target area, and passes the determination result to the background density level detection circuit 8. The background density level detection circuit 8 finds the minimum value of the density of the pixels in the area for the pixels in the detection target area, and outputs this as the background density level.

In the first embodiment, the background density level in the area other than the edge of the image data read by the scanner 1 is detected. In other words, the edge portion of the image data read by the scanner lacks the reliability of the data due to the fact that the original pressing plate is floating. In the present invention, the data at the edge of the image data is excluded from the detection area, which improves the reliability of the data.

FIG. 2 shows a region in the image data which is a target for detecting the background density level. The background detection target area 11 other than the edge 10 of the image data 9 is determined by the coordinate values of the points A and B. At the start of processing, the coordinate values of points A and B are loaded from the CPU (not shown) and set in the register 5. Further, the coordinate value of the pixel of interest is set in the register 6. That is, the coordinate value of the pixel of interest is calculated based on the pixel-by-pixel synchronization signal for driving the scanner and the image processing unit and the line sync signal generated at the time of switching the main scan, and is set in the register 6. The coordinate value in the sub-scanning direction is incremented by 1 each time the line sync signal is set, and the coordinate value in the main scanning direction is incremented by 1 as the sync signal is updated, and becomes 0 when the line sync signal is set. Is reset to.

The coordinate values of the registers 5 and 6 are the area determination circuit 6
Passed to. The area determination circuit 6 compares the coordinate value of the pixel of interest (the coordinate value in the main scanning direction and the coordinate value of the sub-scanning direction) with the coordinate value indicating the detection target area to determine the coordinate value of the pixel of interest. It is determined whether or not it is within the area, and the determination result is passed to the background density level detection circuit 8. The image data after Log conversion is input to the background density level detection circuit 8, and the background density level detection circuit 8 detects the minimum value of the density of the pixel for the pixel determined to be in the detection target area,
This minimum value is output as the background density level.

The background density level detection circuit 8 is not limited to the one described above, and any other circuit or method may be used as long as it can detect the representative value of the background density level in the detection target area. For example, in the detection target area, the average value of the densities of pixels lower than a predetermined density level may be set as the background density level. Further, in addition to the background density level, the configuration can be changed so as to detect and output the hue, brightness, saturation, luminance, etc. in the detection target area. For example, as the hue, the RGB density balance r: g of the background pixel [r, g, b],
The value of r: b is obtained and output.

<Second Embodiment> FIG. 3 shows the structure of a second embodiment. In this embodiment, a document size detection device 11 is provided, and the coordinate value determined as the document region by the detection device 12 is set in the register 5 as a background density level detection target region. The other components are the same as those described in the first embodiment.

The document size detecting device 12 is constructed as follows. That is, the copier is equipped with various sensors, and as a document size detection sensor, for example,
There are a document length detection sensor and a document width detection sensor that detect a standard size (A4, B5, etc.). The document size detection device 12 is composed of such a known document length detection sensor and document width detection sensor. It is also possible to increase the accuracy by increasing the number of sensors.

FIG. 4 shows the result of detecting the size of the original document which is the target of the background density level detection. In the case of a document as shown in the figure, the document area 13 is a document length detection sensor 14 in the main scanning direction and a document width detection sensor 1 in the sub-scanning direction.
5 is detected. The coordinate values A and B obtained from the document size detection result are set in the register 5. The coordinate values A and B are given to the area determination circuit 7 together with the coordinate value of the pixel of interest as values representing the detection target area. The operations of the area determination circuit 7 and the background density level detection circuit 8 are the same as those in the first embodiment, and therefore their explanations are omitted.

<Embodiment 3> Embodiment 3 is an embodiment in which an area designated by an operator is set as a background density level detection target area. FIG. 5 shows the configuration of the third embodiment, in which the document size detection device of the second embodiment is replaced with an area designating editor 16. A schematic configuration of the editor 16 is shown in FIG.

A document 18 is set on a coordinate plate 17 provided in an image processing apparatus such as a copying machine with its surface facing upward, and the operator uses a touch pen 19 to specify two diagonal points. Then, by inputting a predetermined function key, the coordinate values of the two points are set in the register 5. Figure 7
Are the two points A and B designated by the operator on the manuscript.
And the area. The coordinate values A and B are given to the area determination circuit 7 together with the coordinate values of the pixel of interest as values representing the detection target area, and are the same as in the first embodiment.
The area is determined by, and the background density in the area is detected by the background density level detection circuit 8.

<Embodiment 4> The background area of the document is detected by utilizing the fact that the background portion of the document has a picture or character area around the background. In this embodiment, a region sandwiched between a picture or a character region is detected, and this region is used as a density level detection target. FIG. 8 shows a target area for background density level detection. Reference numeral 21 is a reflection signal from the pressing plate, 22 is a signal of the original, 23 is a picture area in the original, 24 is a background, and 25 is a target area for background density level detection sandwiched by the picture area.

FIG. 9 shows the configuration of the fourth embodiment. The picture character area determination circuit 31 detects the picture area and the character area from the image data obtained by reading the original by the image area separation technique. The detection result is stored in order from the head of the line buffer 32 (from right to left in the figure). When the main scan is switched, the contents of the line buffer 32 are copied to the line buffer 33, and then the entire contents of the line buffer 32 are reset. After the main scanning is switched, the above procedure is repeated again. As shown in FIG. 10, the line buffer 33 holds the characters of each pixel on one line and the pattern determination result. In the figure, a pixel determined to be a character or a pattern is represented by, for example, bit 1, and a pixel determined to be other than a character or a pattern is represented by bit 0 and stored in the line buffer 33.

The inter-picture character area determination circuit 35 is a circuit for determining whether or not the pixel of interest exists in an area sandwiched between the pattern or character area. In order to make such a determination, the pixel of interest is selected. The determination result of the image area separation must be obtained for all the pixels of the line including the. for that reason,
The FIFO memory 34 (first-in first-out memory) is used to delay the image data by one line. That is, for the n-th line, when the pattern character area is determined in order from the first pixel, the line buffer 33 stores one line before (n-
1) The separation result of the line is held, and the FIFO memory 3
4 stores image data (density) of each pixel on the (n-1) th line.

FIG. 11 shows details around the line buffer and the FIFO memory. In this figure, one line consists of m + n pixels, the processing of m-1 pixels in the line buffer 32 is completed, and the m-th input pixel P is in the processing state. Therefore, the FIFO memory 34 stores the image data of n + 1 pixels of the line buffer 33 and the image data of m-1 pixels of the line buffer 32.

Since the head pixel of the FIFO memory 34 is the pixel processed one line before, the image area separation result of all the pixels of the line including the head pixel is already set in the line buffer 33. The separation result of the first pixel D of the FIFO memory 34 to be processed now is the line buffer 33.
Is held by the pixel D. Then, the first pixel D is set to F
It is taken out from the IFO memory 34 (shifted to the right by 1 bit), and the area determination processing is performed on the pixel D by the picture character inter-character area determination circuit 35 as described later. Data is FIFO3
4 is written at the leftmost end, and the determination processing of the picture character of the input pixel P is performed, and the determination result is the line buffer 32.
Written in.

The inter-picture character area determination circuit 35 uses a FIFO.
The line buffer 3 corresponding to the first pixel D of the memory 34
Pixels on both sides of the pixel D in 3 are examined, and when a character area or a picture area exists, it is determined as a detection target area of the background density level detection circuit 36. This is shown in FIG.
When the target pixel is A, the pixel A
Has a character area on the right side but does not have a character area or a picture area on the left side, so it is determined that the area is not the detection target area. When the pixel of interest is B or C, there is a character region or a pattern region on both sides of the pixel B or C, so that it is determined to be a detection target region. Pixels B and C (FIF
For example, a flag is attached to the data in the O memory) and the data is output to the background density level detection circuit 36. The background density level detection circuit 36 obtains the minimum density value of the flagged area and outputs the background density level.

When the processing of the first pixel D in the FIFO is completed, the first pixel of the FIFO 34 is E, so the pixel E is taken out and the determination processing is performed as described above with the pixel E in the line buffer 33 as the center. . FIFO 34 1
When the data is shifted to the right by a bit, the data of the next input pixel Q of the current line is stored in the FIFO 34 at the leftmost end of the FIFO 34.
And the character / pattern determination result is written at the position of the input pixel Q of the line buffer 32. FI in the same way
The subsequent pixels F in the FO 34 and the line buffer 33 are processed.

The determination method of the present embodiment is effective even when the density level of the background is high or chromatic because the background is determined if there are character areas or picture areas on both sides of the pixel of interest. is there.

As the above-mentioned image area separation technique, for example, the paper “character / pattern (halftone dot, dot,
Image: Image area separation method for mixed images "(Journal of the Institute of Electronics, Information and Communication Engineers, Vol. J75-DII No. 1 pp39-471)
(See January 992)).

That is, in the detection of the pattern (halftone dot) area, the pixels at the top and bottom of the halftone dot in the local area are detected. Specifically, as shown in FIG. 12, in a 3 × 3 block, the density level L of the central pixel is higher or lower than that of all the surrounding pixels, and the diagonal line is across L and the central pixel. The density levels (a, b) of the pair of pixels existing in the line are | 2 × L−a−b |> TH
When it is (fixed threshold value), the central pixel is defined as a halftone dot pixel.

For the determination of the character (edge) region, for example, the technique described in the above-mentioned paper (see FIG. 10 on p42) is used. FIG. 13 is a block diagram of the character (edge) area detection unit. In the ternarization circuit 41, edge enhancement is applied to the input image data, and then two types of fixed thresholds (TH
, TH2) is used for ternarization. That is, white pixels <
TH1, TH1 ≦ intermediate density pixel <TH2, TH3 <black pixel. The black pixel continuity detecting unit 42 and the white pixel continuity detecting unit 43 detect the regions where the black pixels and the white pixels after the ternarization are continuous by pattern matching.

FIG. 14 shows a pattern for detecting continuity of black pixels, and FIG. 15 shows a pattern for detecting continuity of white pixels. The continuous white pixel and the continuous black pixel that match these patterns are detected and ANDed.
In the circuit 44, when these patterns are matched,
The central pixel is output as a character (edge) area.

<Embodiment 5> Embodiment 5 is an embodiment in which an area near a picture or character area is targeted for background density level detection. FIG. 16 shows the configuration of the fifth embodiment.
The 8-pixel buffer 51 holds RGB pixel data of 7 pixels preceding the pixel of interest on the scan line.
This buffer size is not limited to 8 pixels, and may be any size as long as it can detect a neighboring area. The picture character area determination circuit 52 determines whether the pixel of interest is a picture area or a character area by the image area separation technique, and outputs the determination result, as in the fourth embodiment.

When it is determined that the pixel of interest is a picture or character, the area determination circuit 53 reads the preceding 7-pixel data in the 8-pixel buffer 51 (that is, the area near the picture or character area) (at this time, The parallel data of 7 pixels is converted into serial data and read out) and is output to the background density level detection circuit 54 as a region determination result. FIG. 17 shows a target area for background density level detection.
The background density level detection circuit 54 is similar to that of the first embodiment, as shown in FIG.
The density level is detected for the target area of No. 7.

In the determination method of this embodiment, if the pixel of interest is a character area or a picture area, the area in the vicinity thereof is determined to be the background. Therefore, the determination is effective even when the density level of the background is high or the color is chromatic. Is the way.

<Sixth Embodiment> FIG. 18 shows the first embodiment described above.
13 shows the configuration of an image processing apparatus that uses the background density level detected according to the fifth embodiment. The configuration shown in the figure is a circuit that applies the background density level detected in the first to fifth embodiments to the comparator as the background removal threshold value TH to remove the background and output the background. Input signals (r, g, b) and output signals (r ', g', b ') of this circuit
Is a density linear signal.

The MAX (r, g, b) 62 finds the maximum value of the input signal, and the comparator 61 compares the maximum value of the input signal with the background removal threshold value TH. MAX (r, g,
When b) <TH, the pixel of interest is regarded as the background, the comparator 61 instructs the selector circuit 63 to select (0, 0, 0), and the selector circuit 63 outputs (r ′,
g ′, b ′) = (0,0,0) That is, the signal with the background removed is output. When MAX (r, g, b) ≧ TH, the comparator 61 instructs the selector circuit 63 to select the input signal (r, g, b), and the output signal (r ′, g ′, b ′). ) = (R, g, b) is output.

<Seventh Embodiment> FIG. 19 shows a seventh embodiment of the present invention.
FIG. 4 is a configuration diagram of a color image copying machine of a one-drum system that prints four colors in a frame-sequential manner, scanning four times, and K (black), C (cyan), M (magenta), Y (yellow) at each scan The recording signal is generated in the order of, C,
1 shows the configuration of an image processing apparatus that removes the background when generating M and Y recording signals.

In the figure, the scanner and the Log conversion circuit are the same as those described in the first embodiment, and therefore their explanations are omitted. The color correction processing circuit 71 uses, for example, a linear linear equation for RGB
Color correction processing is performed on the signals as CMYK signals.

C = a0 + a1 * R + a2 * G + a3 * B M = b0 + b1 * R + b2 * G + b3 * B Y = c0 + c1 * R + c2 * G + c3 * B K = d0 + d1 * R + d2 * G + d3 * B where R, G, and B are Log conversions. Later signals, C, M,
Y and K are printer drive signals, a0 to a3, b0 to b3,
c0 to c3 and d0 to d3 are color correction coefficients.

The background removal circuit 72 is provided with a background density level TH.
The background stain of the image data is removed on the basis of the image data, and the multi-valued processing circuit 73 converts the signal C suitable for the gradation expression capability of the printer 74 into C
Convert the MYK signal.

The present invention is characterized by the order of printing. That is, the black (K) plate is printed first, and then cyan (C), magenta (M), and yellow (Y) are sequentially printed, and a total of four scans are performed. Here, K must be printed first, but C,
The printing order of M and Y is not limited to this. And
The background density level is detected during the first scan, and the background removal processing is performed based on the result. Below, FIG.
The operation will be described with reference to the processing flowchart of 0.

During the K plate processing (step 101), the background density level TH is detected by using the method of the first to fifth embodiments (step 102), and TH is held in a predetermined register in the image processing apparatus (step 102). Step 103). The background is not removed during the K plate processing. Then, during the C, M, and Y plate processing, the background density level TH detected during the K plate processing is used as the background removal threshold value, and the background is removed by the method described in the sixth embodiment (step 104). When all the plates have been processed (step 105), the process ends.

The present invention is not limited to the above-mentioned embodiments, and the following modifications can be made. That is, the background removal threshold value applied during the Y plate processing may be a value detected during the C plate processing or the M plate processing before the Y plate, instead of the value detected during the K plate processing. The background removal threshold applied during plate processing may use the value detected during C plate processing instead of the value during K plate processing. Further, the present invention is applicable to any image processing apparatus that scans a plurality of times. Therefore, for example, the background density level is detected during prescanning, and the background removal is performed using the detected value during the main scanning processing. May be.

<Embodiment 8> FIG. 21 shows the color correction process.
1 shows a configuration of an embodiment for performing a color conversion process for converting a background color into a predetermined color. MAX (r, g, b) 81 is the input rg
This is a circuit for obtaining the maximum value from b, and the comparator 82
Is to create a selection signal for the selector 86 by comparing the background density level with MAX (r, g, b), which has the same function as that described in the sixth embodiment. Color correction processing circuit 83
In the same manner as described in the seventh embodiment, the normal color correction coefficient is applied according to the linear linear expression to rgb correct the color to KCMY.

In this embodiment, a background area color correction processing circuit 84 and a color correction coefficient table 85 are further provided. The color correction coefficient table 85 is an RO in which color correction groups are stored.
The color correction coefficient is read from the table according to a designated color (for example, a designated color key is operated), and is set in the background area color correction processing circuit 84 for processing. The circuit 84 performs color correction according to the following equation, and outputs C ′, M ′, Y ′.

C ′ = α0 + α1 × R + α2 × G + α3 × B M ′ = β0 + β1 × R + β2 × G + β3 × B Y ′ = γ0 + γ1 × R + γ2 × G + γ3 × B where α0 to α3, β0 to β3, and γ0 to γ3 are designated. It is the color correction coefficient read from the table 85 according to the color.

It is assumed that a color is designated in advance and a color correction coefficient is set in the background color correction processing circuit 84 before the processing is started. The color conversion process at the time of C, M, and Y plate processing will be described below. The background density level is detected and set in the register or the like during the K plate processing by using the method of the first to fifth embodiments. Then, during each processing of the C, M, Y plates, the maximum value MAX (r, g, b) of the input data r, g, b
b) The comparator 82 compares 81 with the background density level. Maximum value MAX (r, g, b) in comparator 82
The selector 86 selects the output of the color correction processing circuit 84 for the background area when the area is determined to be less than or equal to the background density level, and the selector 86 selects the output of the color correction processing circuit 83 for the area other than that. Select an output. As a result, the background color is converted into the designated color and output.

<Embodiment 9> In this embodiment, in a copying machine in which the number of output gradations of a printer is, for example, 8 gradations, the multi-valued threshold is set when the multi-valued processing is performed for 8 gradations. It is an embodiment in the case of controlling according to. First, the problem in the case where the multilevel threshold is not controlled according to the background density level will be described.

For example, the background density level is 70 (however,
When density is linear data and white is 0 and black is 255), when 8 gradations are simply allocated, each density level is allocated to each corresponding gradation level as shown in FIG. As is apparent from the figure, gradations equivalent to the gradation number 2 are assigned to the densities below the background density level. For this reason, since only 6 gradations are practically assigned to the pattern to be expressed in the actual document, the gradation property of the output image is deteriorated.

Therefore, in the present embodiment, as shown in FIG. 23, a multi-valued threshold value is set so that 8 gradations are assigned to the density higher than the background density level, and the actual gradation number is 8.
The gradation is prevented to prevent deterioration of gradation. Figure 24
Shows the configuration of the multi-value quantization processing circuit 91 shown in the seventh embodiment. In the present embodiment, first, the background density level is detected when the K plate is used, and a multi-value threshold corresponding to the background density level is applied in the multi-value processing at the C, M, and Y plate processing. The multi-value quantization threshold table 92 provided in the multi-value quantization processing circuit 91 is composed of a plurality of tables according to the background density level.

FIG. 25 shows an example of the multilevel threshold table 92. The multi-value threshold table 92 sets the background density level to 3
The tables 93, 94, and 95 are classified and are prepared in advance with values suitable for the respective skin density levels. For example,
When the background density level is 10, the table 93 of the background density levels 0 to 20 is selected, and each threshold value TH of the input density level is selected.
The gradation levels corresponding to 1 to TH7 are assigned. For example, when the input density level is 70, the gradation level 2 is assigned.

Thus, in the multi-value quantization process, the input C, M, Y signals are multi-valued using the multi-value quantization threshold table selected according to the background density level. In addition, K
Since the background density level is not detected in the plate multi-value quantization process, the default (standard) multi-value threshold is applied.

[0058]

As described above, according to the first and second aspects of the present invention, the area for detecting the background density level is
Since it is limited to a specific area in the original image, the detection accuracy is improved.

According to the third aspect of the present invention, the reliability of the image data at the edge portion of the image data read by the scanner is deteriorated when the original pressing plate is lifted. Since the data of the edge portion of is excluded from the detection area, the reliability of the detection data is improved.

According to the fourth and fifth aspects of the invention, the image data read by the scanner includes both the reflection signal of the document pressing plate and the reflection signal of the document. Therefore, when the background density level of the document is detected, it is necessary to distinguish the document from the document pressing plate. In the present invention, the detection accuracy of the background density level is improved by distinguishing the original pressing plate and the original by using the original size detection.

According to the sixth and seventh aspects of the invention, when the original is composed of a plurality of sheets of paper stuck together, there are a plurality of background density levels of the original. For example, if you want to detect either density level when paper with a high density level such as newspaper and paper with a low density level such as high-quality paper are mixed, select the area where the paper exists. By the operator's designation, it becomes possible to reliably detect the background density level of the area.

According to the eighth and ninth aspects of the invention, since the character and pattern information which are the image area separation results are used, even when there is almost no difference in the density level between the document pressing plate and the background portion of the document. , Regardless of the position where the original is set,
The background density level of the original can be automatically detected.

According to the tenth and eleventh aspects of the invention, if the pixel of interest is a character area or a picture area, the area in the vicinity thereof is determined to be the background, so that the background density level is high or the chromatic color In this case, it is possible to make a reliable determination, and the hardware configuration can be simplified as compared with the inventions according to claims 8 and 9.

According to the twelfth and thirteenth aspects of the present invention, in the image processing apparatus which scans a plurality of times, the background density level is detected without pre-scanning when performing the image processing that requires the background density level detection. Therefore, the background removal process can be speeded up.

According to the fourteenth aspect of the present invention, in the image processing apparatus which scans a plurality of times, the background density level can be detected without pre-scanning when performing the image processing that requires the detection of the background density level. In addition, it is possible to perform a predetermined color conversion process at a high speed for an area below the background density level.

According to the fifteenth aspect of the present invention, in the image processing apparatus that scans a plurality of times, the background density level can be detected without pre-scanning when performing the image processing that requires the detection of the background density level. In addition, since the multi-valued processing can be performed at high speed for a region having a background density level or higher, a reproduced image with improved gradation can be obtained.

[Brief description of drawings]

FIG. 1 shows a configuration of a first embodiment of the present invention.

FIG. 2 shows a region in the image data that is a target of detection of a background density level.

FIG. 3 shows a configuration of a second embodiment of the present invention.

FIG. 4 shows a document size detection result which is a target of background density level detection.

FIG. 5 shows a configuration of a third embodiment of the present invention.

FIG. 6 shows a schematic configuration of an editor.

FIG. 7 shows an area designated by an operator.

FIG. 8 shows a target area for background density level detection in the fourth embodiment.

FIG. 9 shows a configuration of a fourth embodiment of the present invention.

FIG. 10 shows characters and pattern determination results of each pixel on one line held in a line buffer.

FIG. 11 shows details around a line buffer and a FIFO memory.

FIG. 12 is a diagram illustrating halftone dot pixels.

FIG. 13 is a block configuration diagram of a character area detection unit.

FIG. 14 is a pattern for detecting continuity of black pixels.

FIG. 15 is a pattern for detecting continuity of white pixels.

FIG. 16 shows the configuration of Example 5 of the present invention.

FIG. 17 shows a target area for background density level detection in the fifth embodiment.

FIG. 18 shows a configuration of a sixth embodiment in which the background is removed and output based on the background removal threshold value.

FIG. 19 shows the configuration of Example 7 of the present invention.

FIG. 20 is a processing flowchart of the seventh embodiment.

FIG. 21 shows the structure of an eighth embodiment for converting the background color.

FIG. 22 is a diagram illustrating a conventional multi-value quantization process.

FIG. 23 is a diagram illustrating a multi-value quantization process according to the present invention.

FIG. 24 shows the configuration of a multi-value quantization processing unit according to the ninth embodiment.

FIG. 25 shows a configuration example of a multi-value threshold value table.

[Explanation of symbols]

 1 Scanner 2 A / D Conversion Circuit 3 Shading Correction Circuit 4 Log Conversion Circuit 5, 6 Register 7 Area Judgment Circuit 8 Background Density Level Detection Circuit

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Claims (15)

[Claims] 1. A means for digitally reading an original,
In an image processing apparatus comprising means for removing a background component based on the background density level of a document included in the read image data and means for outputting the image data after the background removal, the image data is within a predetermined area. The image processing apparatus is provided with a means for determining whether or not there is a background density and a means for detecting the background density level from the image data in the predetermined area. 2. The determining means is means for comparing and determining the coordinate value of the predetermined area and the coordinate value of the image data generated by the main scanning and the sub scanning of the reading means. The image processing apparatus according to item 1. 3. The image processing apparatus according to claim 1, wherein the predetermined area is an area other than an edge of the image data. 4. A means for digitally reading an original,
Image processing including means for detecting the size of the original document, means for removing background components based on the background density level of the original document included in the read image data, and means for outputting image data after background removal An image processing apparatus, comprising: a device for determining whether the image data is within the detected document size; and a device for detecting a background density level from the image data within the document size. apparatus. 5. The manuscript size detecting means is a manuscript length detecting sensor and a manuscript width detecting sensor provided in the reading means, and the judging means determines the coordinate value detected by the sensor and the reading means. 5. The image processing apparatus according to claim 4, which is means for comparing and determining the coordinate value of the image data generated by the main scanning and the sub scanning. 6. Means for digitally reading an original,
Image processing including means for designating an area of the original, means for removing background components based on the background density level of the original included in the read image data, and means for outputting image data after background removal An image processing apparatus, comprising: a device for determining whether or not the image data is in the designated region, and a device for detecting a background density level from the image data in the region. 7. The manuscript area designating means is an editor in which the coordinate values of the area are set by designating a predetermined position of the manuscript on a coordinate plate, and the judging means determines the coordinate values set. 7. The image processing apparatus according to claim 6, further comprising means for comparing and determining the coordinate value of the image data generated by the main scanning and the sub scanning of the reading means. 8. A means for digitally reading an original,
A unit that separates the read image data into a character region or a pattern region, a unit that removes the background component based on the background density level of the document included in the read image data, and the image data after the background removal. In an image processing apparatus having means for outputting, means for determining whether the image data is sandwiched in the separated area, and means for detecting a background density level from the image data sandwiched in the area An image processing apparatus comprising: 9. The determining means comprises a first means for storing a separation result for each pixel in one scanning line by the separating means, and a second means for sequentially storing pixel data of the one scanning line. , Referring to the separation result on both sides of the pixel in the first means, which corresponds to the pixel data extracted from the second storage means, and the extracted pixel data is between patterns or characters or patterns. 9. The image processing apparatus according to claim 8, which is means for determining whether or not there is a space between characters. 10. A means for digitally reading an original, a means for separating the read image data into a character area or a picture area, and a background based on the background density level of the original included in the read image data. In an image processing apparatus comprising means for removing components and means for outputting image data after background removal, means for determining whether or not the image data is in the vicinity of the separated area, and An image processing apparatus comprising means for detecting a background density level from image data in the vicinity. 11. A means for storing a predetermined number of pixel data preceding the read pixel of interest, said determination means reading out a predetermined number of pixel data from said storage means based on the separation result of said pixel of interest. The image processing apparatus according to claim 10, which is means. 12. An apparatus is provided with means for digitally reading an original by scanning the original a plurality of times, and means for removing background components of the original included in the read image data and outputting image data after the background removal. The background density level detecting means according to claim 1, 4, 6, 8 or 10 for detecting the background density level from the image data at the first scan in the image processing apparatus, and at the second and subsequent scans. An image processing apparatus comprising: means for removing the background based on the detected background density level. 13. The background removing means compares the background density level with input image data as a background removal threshold value, and selects a density value of 0 when the input image data is density linear and is less than or equal to the threshold value. 13. The image processing apparatus according to claim 12, further comprising means for selecting the input image data when the input image data exceeds the threshold value. 14. A means for digitally reading an original by scanning the original document a plurality of times, a first means for performing color correction processing on the read image data, and a means for outputting the image data after the color correction processing. A second means for performing color correction processing on the read image data by using a designated color correction coefficient, and a background density level detected from the image data at the time of the first scan. The background density level detecting means described in any one of items 1, 4, 6, 8 and 10, and the second color correction processing means is selected for an area equal to or lower than the detected background density level during the second and subsequent scans. The image processing apparatus further comprises means for selecting the first color correction processing means for an area exceeding the background density level. 15. An image processing apparatus comprising means for digitally reading an original document by scanning it a plurality of times, and means for multi-value-processing the read image data and outputting the image data, at the time of the first scan. The background density level detecting means according to claim 1, 4, 6, 8 or 10 for detecting the background density level from image data, and for the area above the detected background density level during the second and subsequent scans. And a means for performing a multi-valued process by applying a plurality of different thresholds according to the background density level.