JPH05130403A - Subscanning correction device and method therefor - Google Patents

Abstract

PURPOSE:To improve the resolution in a subscanning by giving the pixel data of a current scanning line and the pixel data of a just preceding scanning line to a conversion data storage section as a table address so as to output conversion pixel data. CONSTITUTION:This device is provided with an A/D converter 2, a storage section 4 storing the pixel data of a just preceding read line, and a conversion data storage section 6 storing in advance a conversion value used for conversion of the pixel data. Then the pixel data of the current scanning line and the pixel data of the just preceding scanning line are imparted to the conversion data storage section 6 as a table address to output the conversion pixel data. Thus, correction is implemented by taking the difference of density and the pixel data of the scanning line just preceding to the current scanning line into account. Thus, a level with a sufficient binary value is obtained at a changing point from a white level to a black level or vice versa and the resolution in the subscanning being the original carrying direction is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sub-scanning correction device and a sub-scanning correction method in a facsimile or the like for reading and transmitting image information.

[0002]

2. Description of the Related Art Recently, with the spread of facsimiles,
There has been a demand for low-cost, high-performance devices that can be used at home. Particularly for a reading system, a CCD sensor having higher sensitivity has been widely used as a reading sensor.

However, in a reading system using this reduction optical system, an MTF (Modulation Transfer Function) is used.
Since the resolution represented by is low, it is affected by adjacent pixels,
It has a drawback that the information of the image cannot be read correctly and the thin lines are missing, so that the correct information cannot be transmitted.

[0004]

FIG. 3A shows a state in which the reading cell of the CCD reading unit moves over the original to read the original. The diagonal lines in FIG. 3A indicate black portions on the document. R is a reading surface of one pixel of the CCD reading unit 1, and its width indicates the size of the reading area. Further, FIG. 3A shows a state in which the reading surface of only one pixel moves in the sub-scanning direction (arrow direction).

The analog output of the CCD when the black-and-white pattern is thus conveyed in the direction of the arrow is shown in FIG. 3 (b).

In a conventional facsimile, this analog output is binarized by a comparator or digitized by an A / D converter and then binarized. For this reason,
Regarding the thin line portion S shown in (a), the spatial frequency becomes high at the transition point from white to black or from black to white, and a sufficient level for binarization cannot be obtained. For this reason, thin lines have white spots and blurring.

As prior art, there are methods such as correction by front and rear bits in the main scanning direction (Japanese Patent Publication No. 63-11831) and image correction by digital filter (Japanese Patent Publication No. 63-2517), and these methods improve image quality. Are doing.

However, for example, the former removes the influence of crosstalk in the main scanning as described in the publication, and the effect of image correction in the sub-scanning which is the document conveying direction cannot be expected. Further, the latter method has a problem that it is difficult to reduce the cost because the circuit scale becomes large, and it has been desired to establish a correction method that can be used for low-priced facsimiles.

[0009]

In order to solve the above-mentioned problems, the present invention solves the above-mentioned problems by storing a pixel data of the immediately preceding reading line and a conversion data storage in which a conversion value for converting the pixel data is stored in advance. And the pixel data of the current scanning line and the pixel data of the immediately preceding scanning line are given as table addresses to the conversion data storage unit to output the conversion pixel data. Also, a method of converting the pixel data of the current scanning line into data of a sum of a value obtained by multiplying a difference between the pixel data of the immediately preceding scanning line, that is, a density change amount by a predetermined coefficient, and the pixel data of the current scanning line. did.

[0010]

According to the present invention, with the above configuration, the correction is performed in consideration of the difference in density from the pixel data of the scan line immediately before the current scan line, and the correction is performed at the change point from white to black or from black to white. It is possible to obtain a sufficient level for digitization, and it is possible to improve the resolution in the sub-scan which is the document transport direction.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image correction circuit according to an embodiment of the present invention. In FIG. 1, 1 is a CCD reading unit, 2 is an A / D converter, 3 is an address setting unit, 4 is a RAM for storing the previous line, 5 is an address latch, and 6 is a ROM for converting pixel data. ROM6 for pixel data conversion
Any conversion data can be stored in, and the conversion data is written according to the conversion function.

Reference numeral 7 is a binarization circuit used in a general facsimile. A is the sample and hold clock, and B is
Is a read clock, which is a signal having the timing of this embodiment.

The operation of the image correction circuit configured as described above will be described below. FIG. 2 is a timing chart showing the timings of the signals of the main parts in the block diagram of FIG. 1, and common symbols from A to H are attached to both diagrams.

The sub-scan output for one pixel of the CCD reading section 1 is as shown in FIG. 3 (b). In this figure,
The output value decreases in the thin line portion shown in (a). here,
The reason why the output of the CCD reading unit 1 does not show a rapid reaction to the change in the brightness of the document is that the CCD reading unit 1 outputs the average density in the moving direction. Then, the output of the CCD reading unit 1 is digitized by the A / D converter 2 in accordance with a sample hold clock A (hereinafter referred to as clock A).

Next, the operation will be described step by step. First, according to the clock A, the address setting unit 3 causes the RA for storing the previous line.
An address signal C to be sent to M4 is generated. Then, by sending this address signal C to the RAM 4 for storing the previous line, the reading operation of the previous line data is performed. Then, at the falling timing (t1) of the clock A, the address latch 5
And the previous line data F is output.

After the latch operation, the A / D converter 2 outputs the current line digitized data G in response to the output signal D of the address setting section 3 (t2).

Previous line data F output as described above
The current line digitized data G becomes address information of the pixel conversion ROM 6 and is sent to the pixel conversion ROM 6.
The pixel conversion ROM 6 receives this address information and outputs conversion data H to the binarization circuit 7 in accordance with the read clock from the binarization circuit 7.

It is necessary to store the current line digitized data G in the memory for the correction of the next line. That is, the current line digitized data G is written to the RAM 4 for storing the previous line in synchronization with the clock D (t3). Then, the above operation is repeated for all the dots in the main scanning direction to obtain the conversion data for one line.

Sub-scanning correction in such circuit operation will be described. FIG. 4 shows an example of the correction function. Data of the correction function shown in FIG. 4 is stored in advance in each address of the pixel conversion ROM 6. In this case, there is shown a case where the uncorrected function k is multiplied by a certain multiplier according to the change from the previous line. What is corrected for that change is T
Is a straight line.

Since any data can be written in the ROM, this correction is not limited to the linear function as shown in FIG. 4, but any function can be selected according to the data in the ROM and the input address can be selected. On the other hand, arbitrary data can be output as converted data. That is, the correction function depends only on the setting data of the pixel conversion ROM 6.

In the white thin line portion and the black thin line portion, the CCD output cannot be changed sufficiently as described in the section of the conventional example. Therefore, in the conventional configuration, the output value of the A / D converter may not reach the binarization level as indicated by the symbols I and J in FIG. 3 (c). However, by the correcting means shown in this embodiment, conversion is performed in the directions indicated by the arrows O and P in FIG. 3C to emphasize the change. By this correction, a thin line that does not reach the binarization level can be converted to a binarizable signal.

Next, another example of the sub-scanning correction function will be described. Data of the correction function shown in FIG. 5 is stored in the pixel conversion ROM 6 in advance.

The function of k is in a state without correction, and m is a function obtained by multiplying the function k by the correction coefficient α. Conventionally, FIG.
When a document as shown in FIG. 3A is read, the binarization level does not reach the white thin line portion and the black thin line portion as indicated by symbols I and J in FIG. 3C. If you look at the change from the previous line, you can see that it is changing from black to white or from white to black. Multiplying this change by a predetermined coefficient α, in other words, extends the signal in the directions indicated by arrows O and P in FIG. 3 (c). In this example,
The density variation ΔP = Pij-1-Pij is calculated from the pixel data Pij of the current scanning line and the pixel data Pij-1 of the immediately preceding scanning line, and Qij = Pij + αΔ based on the density variation ΔP.
The pixel data Qij is converted by performing the conversion P.

In FIG. 5, n shows the case where three kinds of correction coefficients are used. In this case, the change is emphasized and corrected in the range from X to Y. In this way, when the coefficient α is switched to a plurality of values according to the value of the current scanning line Pij, it is effective for a minute change, that is, a fine line, and the correction coefficient is set so as not to respond to a thin change in the white or black level. You can also

Although the RAM is used as the front line image storage unit in the above embodiment, it is obvious that the same function can be achieved by using a temporary storage means such as a shift register.

[0027]

As described above, according to the present invention, the MTF correction of the sub-scan can be performed by a simple additional circuit to the conventional facsimile structure, the influence of adjacent pixels can be removed, and the loss of fine lines can be prevented. The quality can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a sub-scanning correction device according to an embodiment of the present invention.

FIG. 2 is a timing chart of the embodiment.

FIG. 3 is a conceptual diagram showing a problem to be solved by the present invention.

FIG. 4 is a graph showing an example of an image conversion method.

FIG. 5 is a graph showing an example of an image conversion method.

[Explanation of symbols]

 1 CCD reading unit 2 A / D converter 3 address generation unit 4 front line storage RAM 5 address latch 6 pixel data conversion ROM 7 binarization circuit

Claims (3)

[Claims] 1. A device obtained by scanning a document for scanning.
An A / D converter that converts the luminance signal of the main scanning line into a pixel data string of a plurality of bits, a storage unit that stores the pixel data of the immediately preceding reading line, and a conversion value that converts the pixel data are stored in advance. A sub-scan comprising a conversion data storage unit, and outputting the conversion pixel data by applying the pixel data of the current scanning line and the pixel data of the immediately preceding scanning line to the conversion data storage unit as table addresses. Correction device 2. The pixel data of the current scanning line is converted into the sum data of the difference between the pixel data of the immediately preceding scanning line, that is, the density variation multiplied by a predetermined coefficient, and the pixel data of the current scanning line. A sub-scanning correction method characterized by: 3. The sub-scanning correction method according to claim 2, wherein a plurality of coefficients are switched according to the pixel data of the current scanning line.