JPH01303578A - Picture converting device - Google Patents

Abstract

PURPOSE:To realize the linear density conversion of high-quality pictures regardless of a white or black ground picture by applying the density of a picture to be processed to the conversion of an inverted picture and at the same time giving the second density inversion to the converted picture to output the inverted picture after returning it to the original picture property. CONSTITUTION:The black/white inverting circuits 5 and 6 serving as the density conversion means which invert the picture density are set at the picture input and output parts of a picture processor consisting of a line buffer 1, a converted picture element position detecting circuit 2, a picture element extracting circuit 3 and a conversion arithmetic circuit 4. Then the density of an input picture is inverted according to the property (white or black ground picture) of the input picture. This inverted density is applied to the linear density conversion carried out by the picture processor and at the same time the density of an output picture undergone the linear density conversion is inverted and outputted. Thus a high-quality linear density converted picture is simply obtained with no change caused to a conversion parameter even in case only a conversion parameter is set at the circuit 4 with preference given to the black picture elements.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an image processing device that performs linear density conversion on a human image to obtain an enlarged/reduced output image.

(Prior Art) One of the important techniques in image processing is image enlargement/reduction processing using linear density conversion. Image enlargement/reduction processing using this linear density conversion is performed, for example, by finding the corresponding position on the input image of each pixel of the image to be converted and output as the converted pixel position, and using pixel information around the converted pixel position on the input image. Pixel information of the image to be converted and output is determined by performing a predetermined calculation. However, the processing load changes significantly depending on how much pixel information around the converted pixel and position is referenced, and if the number of reference pixels (reference pixel range) is limited, the flexibility of enlargement/reduction processing is impaired. , and problems such as deterioration of the image quality of the converted image occur.

To solve this problem, a smoothing function is introduced into the calculation performed on pixel information around the converted pixel position, and by smoothing and sampling the smoothed image, it is possible to easily perform enlargement/reduction conversion at any magnification. For example, Japanese Patent Application Laid-Open No. 56-903
This is proposed in Publication No. 75, etc. However, from a practical standpoint, the following problems remain.

That is, when performing a reduction conversion of a character/line drawing image, the parameters of the conversion process are set so as to give priority to black pixels for boat fishing. This is because if you set a conversion parameter that does not change the black-white density ratio and perform the reduction conversion of the above text/line drawing images, the important image information of black pixels will be lost, resulting in so-called blurred characters and missing lines. This is done for the purpose of preventing problems such as those that may occur.

However, the text/line drawing images targeted for conversion processing are not necessarily those with text/line drawings drawn using black pixels on a white background, but must be black originals with text/line drawings drawn using white pixels on a black background. There is also. If the above-mentioned conversion process giving priority to black pixels is applied to such a black background original, a problem arises in that most of the white characters and white lines become black. Therefore, in such cases, it has been considered to provide conversion parameters that give priority to white colors, but it is also possible to prepare multiple conversion calculation circuits with different conversion parameters, or to change the conversion parameters each time depending on the image to be processed. There were problems such as the need to change settings.

(Problem to be Solved by the Invention) As described above, in the conventional image processing device using linear density conversion, conversion parameters are set to exclusively prioritize black pixels and execute the conversion process. If a black background original is converted as it is, there is a major problem in that the white characters and white line drawings become black.

The present invention has been made in consideration of these circumstances, and its purpose is to provide an image with a simple and highly practical configuration that can perform high-quality enlargement/reduction conversion even on black originals. The purpose of this invention is to provide a processing device.

[Structure of the Invention] (Means for Solving the Problems) As the schematic structure of the image processing device according to the present invention is shown in FIG. 1, line buffers y1. A black-and-white inversion circuit 5.8 as a density conversion means for inverting image density is provided in the image processing section and image output section of the main body of the image processing apparatus, which is composed of a conversion pixel position detection circuit 21, a pixel extraction circuit 3, and a conversion calculation circuit 4.
and invert the density of the input image according to the nature of the input image (white background image or black background image) and subject it to linear density conversion by the image processing device main body, and also invert the density of the output image after linear density conversion. This feature is characterized in that it is output as follows.

(Function) According to the image processing apparatus according to the present invention, which is configured with the black and white inversion circuit 5.6 that inverts the density of the image as described above,
As shown in FIG. 2, the processing concept is shown, even if only the conversion parameter that gives priority to black pixels is set in the conversion calculation circuit 4, a black background original is reversed and treated as a white background image, and this white background image is converted into a white background image. It is now possible to apply linear density conversion to the image, invert the black and white again, and output it as a linear density converted black background image, easily obtaining a high quality linear density converted image without changing conversion parameters. becomes possible. Therefore, it is possible to apply effective image conversion to both the white background image and the black background image. Moreover, since it is sufficient to provide a black-and-white inversion circuit as a density conversion means and control its inversion operation, the apparatus cost is low and the apparatus is highly practical.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 3 is a schematic diagram of an apparatus according to an embodiment of the present invention.

In FIG. 3, l is a line buffer that stores an image to be processed and is used for linear density conversion processing, and for example, a 4-line buffer is used. The converted pixel position detection circuit 2 calculates, as a converted pixel position, the position on the input image corresponding to each pixel of the output image to be output after linear density conversion, and the pixel extraction circuit 3 uses information on the converted pixel position. Accordingly, input pixel data around the converted pixel position is selectively extracted from the line buffer 1. In addition, the external area clear circuit 3a
In this case, an external area of the input image is referred to as pixel data around the converted pixel position. Convert the pixel data corresponding to the external area to background density (for example, white pixel data) (
clear).

The conversion calculation circuit 4 performs predetermined calculation processing on the input pixel data around the converted pixel position extracted by the pixel extraction circuit 3 to obtain each pixel data of the output image. . This conversion process is performed, for example, by setting a black pixel priority parameter as described later.

The black-and-white inverting circuit 5 provided in the input section of the image processing apparatus main body (previous stage of the line buffer l), which is composed of the above-mentioned circuits, adjusts the density of the image to be processed (input image) given via the input interface 7. The image is inverted according to the nature of the image, stored in the line buffer 1 as a white background image, and subjected to linear density conversion. Further, a black-and-white inversion circuit 6 provided at the output stage of the image processing apparatus main body (the subsequent stage of the conversion calculation circuit 4) outputs an output image from the conversion calculation circuit 4 in response to the operation of the black-and-white inversion circuit 5 in the input stage. This is to invert the black and white. The output image obtained by linear density conversion is output from this black-and-white conversion circuit 6 via an output interface 8. In this way, the black and white inverting circuits 5 and 6 provided at the input and output stages of the main body of the image processing apparatus are
Thus, first and second density conversion means for inverting the l density of the image to be processed are realized.

Note that 9 is a control circuit that controls the operation of each of these circuits and controls the sequence of image enlargement/reduction processing by linear density conversion. This control circuit 9 exchanges various control commands and execution parameters with an external CPU via the CPU bus, and executes the processing operations. Also, here, the input interface 7. Input/output of image information via the output interface 8 is performed with a predetermined external device via an image data bus.

To explain in more detail each part of the apparatus of this embodiment configured as described above, first, the black and white inverting circuit 5.6 is an exclusive OR circuit (EX) as shown in FIG. 4(a), for example.
-OR), the pixel data (binary) and the white background/black background identification information (2fifi) are configured to be subjected to exclusive OR processing. In addition, as shown in FIG. 4<b>, it is configured to perform the same type of processing using an exclusive NOR circuit (EX-NOR) and an inversion circuit (INV), or as shown in FIG. 4(e). The inverted pixel data and non-inverted pixel data are transferred to a multi-bruxer (MP) using an inverting circuit (INV).
X) for selective extraction.

The black-and-white inversion circuit 5.8 configured as described above performs density inversion processing on a white background image to a black background image, and a black background image to a white background image. The operation of the first black-and-white inversion circuit 5 provided at the input stage is controlled under the control of the control circuit 9 so that the output image becomes a white background image. By this operation control, if the input image is a white background image, the white background image is output to the line buffer 1 as is, and if it is a black background image, it is inverted to a white background image and output to the line buffer 1. Further, the second black-and-white inversion circuit 6 on the output stage side responds to the operation of the first black-and-white inversion circuit 5, and only when the black-and-white inversion circuit 5 executes the inversion processing operation, the second black-and-white inversion circuit 6 receives the signal from the conversion calculation circuit 4. Performs inversion processing on the output image.

Now, FIG. 5 shows an example of the configuration of the converted pixel position detection circuit 2. In FIG. As shown in Figure 11, the distance between pixels (indicated by 0 mark in the figure) of the human image is normalized as "1", and the distance between pixels (indicated by X mark in the figure) of the enlarged/reduced output image is " S”
, the conversion magnification r is expressed as (1/s). Furthermore, the pixel position (sampling position) i on the input image corresponding to the j-th pixel of the output image is the i-th pixel position on the input image that satisfies i=[5-jl, where [k is a Gaussian symbol] from tms
・It can be considered as a position with a minute displacement of j-1.

FIG. 5 shows the column direction (X
This shows an example of the configuration of a pixel position detection unit in the pixel position detection section in the
The converted pixel position detection circuit 2 is realized using two sets of directional pixel position detection units. The first register 2a stores the integer part (i) of the data indicating the sampling interval S, and the second register 2b stores the decimal part (i) of the data indicating the sampling interval S.
) is stored. The respective parts stored in these registers 2a and 2bi are given to adders 2c and 2d, and are sent to latch circuits 2e and 21' according to the clock CP-CNV.
will be taken in sequentially. Note that the adders 2c and 2d input the latch data of the latch circuits 2e and 2r to the registers 2a and 2d.
It cumulatively adds the data given from 2b,
The carry signal of the adder 2d that cumulatively adds the decimal part data is given to the adder 2c that adds the integer part data, and its addition output value is incremented by (+1). These adders 2c,
2d and latch circuits 2e and 2f', the converted pixel positions are sequentially updated in synchronization with the clock CP-CNV.

On the other hand, the counter 2g counts the clock CP-ORG to determine the pixel scanning position of the input image. This counter 2
The data of the scanning pixel position of the input image counted by g and the data of the converted pixel position obtained by the latch circuit 2e are compared by the comparator 2h, and when these data match, the conversion calculation request signal RQ-CNV is output. Emitted.

Such conversion coordinate position detection processing is performed in the X direction (main scanning direction) and Y direction (sub scanning direction) of the image to be processed, and the timing at which the conversion calculation request signal RQ-CNV is issued from both directions is , the converted pixel position is identified.

In the above-mentioned pixel position detection in the X direction, each time one row of pixel scanning is completed, the latch circuits 2e and 2r are cleared and pixel position detection in each row is performed.

Now, FIG. 6 shows the circuit part of the pixel extraction circuit 3 which operates in response to the conversion operation request signal RQ-CNV from the conversion pixel position detection circuit 2 configured as described above. It is shown together with the area clear circuit 3a.

Specifically, the line buffer l is 4 as shown in FIG.
It is implemented as a 4-line buffer that sequentially stores pixel data for lines. The pixel extraction circuit 3 stores pixel data that is output in parallel from this 4-line buffer 1 for each 4 pixels in the column direction over a range of (4×4) pixels (4×4).
It is composed of registers 3b, and a multiplexer 3c that performs image rotation processing and extracts the pixel data stored in these registers 3b.

To briefly explain the rotation process of the extracted pixel by the multiplexer 3c, the reference pixel in the (4×4) pixel area is shown in FIG.
Noting that the conversion calculation result is the same in the case shown in b), the converted pixel position becomes a second quadrant formed by dividing the original pixel into four, as shown in Figure 12. By selectively extracting pixel data in this manner, the redundancy of the conversion calculation described above is removed.

Basically, for the pixel extraction circuit 3 configured as described above, the external area clearing circuit 3a controls the input of pixel data to the line buffer l and the gate circuit 3es that controls the input of pixel data to the (4×4) pixel area to the register 3b. A shift register 3r and four gate circuits 3 control the storage of pixel data.
g, 3h, to 3j.

That is, the converted pixel position is determined and the surrounding (4×4)
When attempting to perform arithmetic processing for linear density conversion by referring to pixel data in a pixel area, depending on the converted pixel position, as illustrated in Figure 7, the converted pixel position may be identified as the boundary of the input image. In this case, even external areas other than the input image area may be referenced. When such pixel data in the external area is stored in the line buffer 1, its value is usually undefined, and there is a problem in using this undefined value as it is for conversion calculations.

Therefore, the external area clear circuit 3a prevents the input of pixel data before the start of scanning of the input image and after the end of scanning with the gate circuit 3e provided at the input stage of the line buffer l, and also prevents the input of pixel data in the pixel scanning line in the row direction. Input of pixel data before the beginning and after the tail is blocked. Regarding the operation of storing data in line buffer l, first clear all of line buffer l to zero (0), and then store the entire input image including the external area referred to as a (4x4) pixel area in the conversion calculation. During this period, the data is manually controlled such that the pixel data is stored in the line buffer l. As a result, only pixel data within the image area is input to the line buffer 1, and a data value of "0#" is stored in each data storage position corresponding to a pixel portion outside the area on the line buffer 1. It's like that.

Thus, the shift register 3a transfers the pixel data of the (4×4) pixel area read from the line buffer l and stored in the register 3b to its line scanning position (sub-scanning position).
It clears each row according to the specified conditions. Specifically, as shown in FIG. 8, a clear signal is output from the foot register 3r to prohibit data storage of pixel data outside the area to the register 3b according to the reference position of the original image, and the pixel data outside the area is is cleared to “0”. In other words, Fig. 8 (a
), Pll, ~P14. in the (4×4) reference pixel area. P21. ~P24.
P31. ~ In order to clear each of P34, [0
A clear signal 0011 is output from the register 3f and is applied to the register 3b. By controlling data storage in the register 3b using such a shift register 3r, the data of the reference pixels that are the external area of the input image are each reset to zero (0).

Through the processing procedure described above, among the pixel data of the (4×4) reference area read out from the pixel extraction circuit 3, the pixels corresponding to the external area are cleared to zero (0) and given to the conversion calculation circuit 4'. It will be done.

Now, this conversion calculation circuit 4 includes, for example, a plurality of adders (ADD) as shown in FIG.
a, and a comparator 4C that determines the value of output pixel data by discriminating the number of black pixels counted by the black pixel number counter 4a using a predetermined threshold selected by a multiplexer (threshold selection circuit) 4b. Ru.

As illustrated in FIG. 10, the multiplexer 4b recognizes that when characters and line drawings are converted using a high threshold value that keeps the black-and-white ratio constant, blurring of characters occurs, and a low threshold value that does not cause blurring of characters. Focusing on the fact that when a conversion operation is performed on a so-called filled image, the black-and-white area ratio changes significantly, we selected a low threshold value that realizes a conversion operation that prioritizes the line components for characters and line drawings, and in the case of filled images. In this case, a high threshold value is selected that realizes a conversion operation that does not change the black-white area ratio. Note that this threshold selection control is performed depending on the type of image to be processed.

That is, a threshold value (for example, 16
When the number of black pixels in a (4×4) pixel area is discriminated using a threshold value [8] for 6 pixels, in a line image as shown in FIG. 13(a), the converted pixel data is (0
), resulting in the blurred characters mentioned above. Therefore, for such character/line images, priority is given to black pixels, and a low value of [3], for example, is set as the threshold value to perform the conversion calculation. According to such a low threshold value, the converted pixel data including line drawings and parts as reference pixel areas becomes (1), so that line density conversion can be realized giving priority to black pixels.

On the other hand, when a filled image as shown in FIG. 13'(b) is subjected to linear density conversion using the above-mentioned low threshold value, all of the converted pixel data that uses the filled image part as the reference pixel area becomes (1
), and the black line width becomes undesirably thick. In this case, the line width of 4 pixels is expanded to 6 pixels. Therefore, in such a case, the above-mentioned high threshold value is selected and the linear density conversion is performed using a conversion calculation that keeps the black-white ratio constant.

By counting the number of black pixels in the reference pixel area, controlling the selection of the threshold value, and discriminating the number of black pixels using the selected threshold value, an image that well reflects the information of the original image as shown in FIG. 10 is created. A linear density conversion of is realized.

Note that the threshold value for character/line images in the conversion calculation circuit 4 is effective for character/line images drawn with black pixels on a white background. However, if the character line is drawn with white pixels on a black background, - for boat fishing, instead of using the low threshold value that realizes the conversion calculation that gives priority to black pixels, the conversion threshold value that gives priority to white pixels is set. It is necessary to set an even higher threshold to execute this, but in this case, by using the black-and-white inversion process described above,
Since the line image is subjected to a conversion process in which the line image is inverted into a character line image on a white background, the processing procedure is performed in exactly the same way as the process for a character line image on a white background using the above-mentioned low threshold value.

According to this device configured in this manner, in order to achieve high-quality density conversion for text and line drawings, conversion calculations that give priority to black pixels are set, and under such conditions, white pixels on a black background are Even when converting the line density of drawn characters/line drawings, the density of the human image is inverted and used for image conversion, so there is no need to change the format of the conversion calculation.
Image enlargement/reduction can be achieved directly by high-quality linear density conversion. In addition, regarding the external area clearing means described above, the external area is (
0) clearing, the external area can be set to the density of the background part as it is by means of zero (0) clearing. Therefore, the density inversion means and the external area clearing means effectively cooperate to easily realize high-quality linear density conversion.

As a result, regardless of whether the image to be processed is a character/line image on a white background or a character/line image on a black background, high-quality image line density conversion can be achieved under simple processing control. becomes possible.

Note that the present invention is not limited to the embodiments described above. Although a binary image has been described here as an example of an image to be processed, the present invention can be similarly applied to an image having gradation. In this case, instead of the black-and-white density inversion circuit described above, a circuit that inverts each density level from the lowest density value to the highest density value may be used. Furthermore, if line density conversion giving priority to white pixels is set, the white background image may be inverted. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the input section and the output section of the main body of the apparatus for converting the linear density of an input image to obtain an enlarged/reduced image are provided with a density inversion means, and the processing target is appropriately adjusted. The density of the image is inverted, the image is subjected to conversion processing, and the image that has been subjected to image conversion processing is again processed to invert the density to restore the original image properties before being output. Great practical effects such as the ability to realize image density conversion can be achieved.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Figure 1 is a schematic configuration diagram of an image processing device according to the present invention, Figure 2 is a conceptual diagram showing the basic processing functions of the present invention, and Figure 3 is a conceptual diagram showing the basic processing functions of the present invention. The figure is an overall configuration diagram of the embodiment device, and FIG. 4 is a diagram showing an example configuration of a black and white inversion circuit.
FIG. 5 is a diagram showing an example of the configuration of a converted pixel position detection circuit, and FIG.
The figure shows an example of the configuration of a line buffer and pixel extraction circuit.
Figure 7 is a diagram showing the concept of the pixel reference area in the conversion process, Figure 8 is a diagram to explain the clearing process for the external area included in the pixel reference area, and Figure 9 is a diagram showing an example of the configuration of the conversion calculation circuit. 10 is a diagram showing an example of a threshold value used in a conversion calculation and a processed image. FIGS. 11 and 12 are diagrams for explaining the basic concept of image linear density conversion processing.
The figure is a diagram for explaining changes in a converted image due to differences in conversion thresholds. DESCRIPTION OF SYMBOLS 1... Line buffer, 2... Conversion pixel position detection circuit, 3... Pixel extraction circuit, 4... Conversion calculation circuit, 5
, 1S...black and white inversion circuit (density inversion means). Applicant's representative Patent attorney Takehiko Suzue 113 Figure 4 Figure 7 Figure 8 (a) (b) Figure 411 (a) (b) Figure 912

Claims (1)

[Scope of Claims] An image conversion device for linear density converting an input image to obtain an enlarged/reduced output image, comprising: a first image converter for inverting the density of the input image according to the properties of the input image and subjecting it to the linear density conversion; and a second density converting means for inverting and outputting the density of the linear density-converted output image in response to the first density converting means. Device.