JPH03165663A - Pixel density conversion method and device - Google Patents

Abstract

PURPOSE:To simultaneously execute both processings and to enable a sharpening processing with the small number of picture elements by constituting a coupled operator while combining the operator of a picture element density conversion processing and the operator of the sharpening processing. CONSTITUTION:The sharpening processing and an interpolating method as the substance of picture element density conversion are based on the same kind of principle filtering arithmetic and the calculation procedure is the same as that of the value of a certain picture element by the sum-of-products arithmetic of the coefficients corresponding to the values of peripheral picture elements. Since the coupled operator is constituted by combining the operator of the picture element conversion processing (the set of sum-of-products coefficient) and the operator of the sharpening processing, both the processings can be simultaneously executed. Then, the source picture element to be referred in the case of the sharpening processing is limited only to the source picture element on the same line as the source picture element to be sharpened. Thus, the sharpening processing can be executed with a small number of picture elements.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a pixel density conversion method and apparatus, and in particular, to convert image data formed at a first pixel density into a second pixel density, which enables simultaneous processing of pixel density conversion and sharpening of an image. The present invention relates to a method and apparatus for converting pixel density into density data.

[Conventional technology]

For example, when an image is input to an auxiliary storage device at a suitable resolution using a layout scanner, etc., and output at a desired size to a hard copy device with a different pixel density, such as a printer. , it is necessary to convert the pixelization degree to match. Conventionally known pixel density conversion methods include the nearest Naper method, in which the data of the original pixel closest to the pixel position to be converted is used as the pixel data to be converted; The pi-linear method calculates the data of the pixel to be converted by performing linear interpolation on the surrounding original pixel data, and the cubic method calculates the data of the pixel to be converted by performing curve interpolation on the data of the original pixels surrounding the pixel to be converted.
There are convolution methods, etc. On the other hand, image sharpening processing is required to correct the characteristics of a hard copy device or the like and the sharpness of an image degraded by the pixel density conversion. Conventionally known sharpening methods include methods that use the Laplacian to emphasize changes in data by subtracting the second-order differential value of the data from the original data, and methods that use corrections to the Laplacian. There is a method using the differential operator.

[Problem to be solved by the invention]

However, in the conventional technology, since the pixel density conversion process and the sharpening process are performed independently, it is necessary to either perform the sharpening process on the image after converting the pixel density, or Or, conversely, the image density of the image after sharpening processing is converted. Even if pixel density conversion and sharpening processing are performed at the same time, compared to performing only one of them, There are problems in that many pixels are referenced during processing, a large capacity memory is required, and the processing time is long. The present invention was made to solve the above-mentioned conventional problems, and provides a pixel density conversion method and device that can perform pixel density conversion processing and sharpening processing at high speed and with a small memory capacity. The task is to do so.

[Means to achieve the task]

The present invention provides image data formed with a first image N density,
In the pixel density conversion method for converting into second pixel density data, the operator of the sharpening process limits the original pixels to be referred to for the sharpening process to only the original pixels on the same line as the original pixel to be sharpened. The above object is achieved by configuring a combined operator that combines an operator for pixel density conversion processing and an operator for sharpening processing, and simultaneously performing pixel density conversion processing and sharpening processing using the combined operator. be. The present invention also provides a combination of a pixel density conversion processing operator and a sharpening processing operator in a pixel density conversion device that converts image data formed at a first pixel density into second pixel density data. an operator table in which an operator is stored in correspondence with the relative position of the pixel to be converted with respect to the position of original pixels surrounding the pixel to be converted;
a relative position determination unit that determines the relative position of the pixel to be converted with respect to the original pixel position; and a product-sum unit that reads a combination operator corresponding to the relative position from the operator table and performs a product-sum operation on data of the pixel to be converted. By configuring the operator of the sharpening process to limit the original pixels to be referred to for the sharpening process to only the original pixels on the same line as the original pixels to be sharpened, the above problem can also be solved. has been achieved.

[Effect]

In the present invention, the sharpening process and the interpolation method, which is the essence of pixel density conversion, are based on the same principle in the sense of filtering operations, and the pixel value of interest is calculated by the sum of products of surrounding pixel values and corresponding coefficients. This was done by focusing on the fact that the calculation procedures are the same. That is, in the present invention, image processing is performed simultaneously by configuring a combined operator that combines an operator for pixel density conversion processing (a set of product-sum coefficients) and an operator for sharpening processing. Further, by limiting the original pixels to be referred to during the sharpening process to only the original pixels on the same line as the original pixel to be sharpened, the sharpening process can be performed with a small number of pixels. Therefore, pixel density conversion processing and sharpening processing can be performed at high speed and with a small memory capacity.

【Example】

Below, with reference to the drawings, images that have been sharpened using a 3X1 operator are processed using linear interpolation in the main scanning direction.
An embodiment of the present invention will be described in detail by taking as an example a case where pixel density conversion is performed using the nearest neighbor method in the sub-scanning direction. Figure 1 explains the principle of this embodiment, and shows that the pixels to be converted, including data such as their gradation values, are expressed as P (k%).
As the original pixels surrounding this pixel P (k. bu) to be converted, a total of four original pixels 0 (m, j)
, m5-(i-1, i, i+1, i+2). Here, regarding the distance between the pixel P (k, β) to be converted and the original pixel 0(i, j), let the horizontal component in FIG. 1 be X and the vertical component be y. In this embodiment, since the pixel density is converted using the nearest neighbor method in the sub-scanning direction (vertical direction in the figure), the line closest to the pixel P(k, i) in the sub-scanning direction,
That is, the line of original pixel 0 (m%j), l-..., r-
1, r, r+1, +2, . . . are used to calculate the processed data (gradation value) of the pixel P (k. β) to be converted. In other words, the original pixel referred to for the sharpening process of the original pixel 0(i, j) is only the original pixel 0(III, j) on the same line as the original pixel O(i, j) to be sharpened. shall be limited. Now, an intermediate pixel 0''( The data (gradation values) of i, j) are calculated using the following formula % () ) () (1) Here, the coefficients aoS al, al are weighting coefficients corresponding to the Laplacian, for example.Similarly, Then, another original pixel 0 (i+1, j) is created with an intermediate pixel 0-, which is on the same line as the original pixel 0 (i+1, j) and has undergone sharpening processing using a 3×1 operator around it.
< i+1 , j ) is found. Therefore, the two intermediate pixels 0'(i
, j ), and t-(i+1, j), to obtain the data (gradation value) of the pixel P (k, bu) to be converted by linear interpolation, the following calculation is performed: good. P(k, 1) −(1−x)・0−(i, j) +X・O(i+1, j) (2) Above (1)
When formula (2) is combined, the pixel P to be converted is
The data (gradation value) after performing the sharpening process and pixel density conversion of (k, A) is expressed by the following equation. P(k, J2> -bo・0(i-1, j) + b, ・O(i, j+b2 ・Q(i+1, j) + b, ・O(i+2, j)...
... (3) Therefore, b, Sb, , b2, b3 becomes 4
By using four ×1 operators, simultaneous processing of pixel density conversion and sharpening can be realized. Further, by limiting the original pixels to be referred to for the sharpening process to only the original pixels on the same line as the original pixel to be sharpened, the sharpening process can be performed with a small number of pixels. Therefore, pixel density conversion processing and sharpening processing can be performed at high speed and with a small memory capacity. In addition, in the above explanation, the coefficient equivalent to performing sharpening first and pixel density conversion afterwards is calculated, but conversely, the coefficient equivalent to performing pixel density conversion first and sharpening afterwards is calculated. It is also possible to obtain and use the coefficients. Further, although the Laplacian is used for sharpening, other differential operators may be used. Although the nearest neighbor method was used, other interpolation methods such as cubic conpolysicon may be used to construct the operator. FIG. 2 shows an actual configuration of the pixel density conversion device 10 for simultaneously performing pixel density conversion and sharpening processing according to the above embodiment. In this embodiment, for example, a layout scanner or the like is used to combine an input image memory 12 in which original pixel data formed at a first pixel density is stored, an operator for pixel density conversion processing, and an operator for sharpening processing. The combined combination operator (1) o, bt, b2b3) transforms the pixel P(k
Determine the operator table 14 stored in correspondence with the relative position X of the pixel to be converted with respect to the position of the original pixel 0 (m, j>) surrounding ll, and the relative position X of the pixel to be converted with respect to the original pixel position. The relative position determination unit 16 reads the combination operator corresponding to the relative position According to equation (3), pixel data P(k, l
an output image memory 20 that stores the data of pixels to be converted calculated by the product-sum calculation section 18 and prepares for output from a printer or the like; and the relative position determination section. 16, and a controller 24 that controls the input image memory 12 and the output image memory 20 via the address calculation section 22. The operator of the sharpening process is configured to limit the original pixels to be referred to for the sharpening process to only the original pixels on the same line as the original pixels to be sharpened. In the operator table 14, 4× of the above-mentioned equation (3)
1 operator boS b+, bz, b3 values are stored. This operator boS bl, bl, b
The value of 3 is uniquely determined by the relative position X. Therefore, the area including the pixel P(k, j2> to be converted and surrounded by several original pixels 0(m, j)) is divided into multiple partial areas with respect to the value of X, and an operator is applied to each partial area. By limiting the value of
The result will be as shown in the figure. Since the operators bo, b1, bl, and b3 in the area surrounded by the broken line in Fig. 3 have the same value,
Relative position between the pixel P (k, β) to be converted and its two neighboring original pixels 0(i, j>, 0(i+1, j>)
Once b is determined, the operator b to be used in the calculation is determined by determining which partial region the relative position falls under.
,, bl, bl, b3 are determined. In the case of this example,
There are 4 partial areas, operators bo, b, , b2, b
Since there are also four sets of 3, these are stored in the operator table 14. The operation of the embodiment will be explained below with reference to FIG. After the address of the pixel P (k, λ) to be converted is determined by the controller 24, the process proceeds to step S1, and the relative position determination unit 16 determines that the pixel P<k, a) to be converted is the pixel to be converted. Original pixel 0(i 1j
>, O(i+1, j), region determination is performed to determine which partial region it is included in. Next, the process proceeds to step S2, and among the operators assigned to each partial area, the operator of the partial area to which it belongs l)
o, bt, l) Read 2, b3. Next, the process proceeds to step S3, and the data (gradation value) of the pixel P (k. β) to be converted is calculated using the read coefficients according to the above equation (3). By repeating this for all converted pixels, the tone value of each converted pixel is determined, and the determined tone value is stored in the output image memory 20. FIG. 5 shows the configuration of an application example in which the pixel density conversion device 10 according to the present invention is employed. In FIG. 5, high-density pixel data of approximately 12 to 20 pixels/deg. is taken in by the layout scanner 30, and is transferred to the controller 32 including the functions of the controller 24 (FIG. 2). Memory 3 including the functions of input image memory 12 and output image memory 20 (FIG. 2)
4 is stored. The pixel data stored in the memory 34 is provided to the pixel density conversion device 10 according to the present invention via the controller 32 to perform the process according to the present invention. The data after being subjected to pixel density conversion and sharpening processing as shown in FIG. 6 in accordance with the pixel density of a hard copy device such as a printer (usually lower than the input data) is stored again in the memory 34 and used later. It is read out and provided to a hard copy device such as a printer. In this embodiment, when storing the operator table 14, the area sandwiched by two original pixels 0(i,j) and O(i+1,j) near the pixel P(k,l) to be converted is is divided into four partial areas, and a set of coefficients , b, , b, , b3 is determined and stored for each partial area, so that the corresponding coefficients can be quickly read from the operator table. It can be easily implemented in hardware. Note that the number of original pixels and the number of partial areas including pixels to be converted are not limited to these. Furthermore, a combination operator may be determined without dividing the region into partial regions. Further, in the embodiment described above, the combination operator is constructed using four coefficients (4×1), but the number of coefficients that constitute the combination operator is not limited to this.

【Effect of the invention】

As explained above, according to the present invention, a combined operator is configured by combining an operator for pixel density conversion processing and an operator for sharpening processing, so that image processing can be performed simultaneously, and at the time of sharpening processing. The original pixel to be referred to,
Since the sharpening process is limited to only the original pixels on the same line as the original pixels to be sharpened, the sharpening process can be performed with a small number of pixels. Therefore, an excellent effect can be obtained in that the sharpening process and the pixel density conversion process can be performed at high speed and with a small memory each time.

[Brief explanation of the drawing]

The first factor is a diagram showing the relative positional relationship between the pixel to be converted and the original pixel for explaining the principle of the embodiment of the pixel density conversion method according to the present invention. A block diagram showing the configuration of an embodiment of the adopted pixel density conversion device,
FIG. 3 is a diagram showing the relative positional relationship and partial areas between pixels to be converted and original pixels, for explaining the state of data stored in the operator table used in the embodiment; FIG. 4 is a flowchart showing the processing procedure of the embodiment, FIG. 5 is a block diagram showing the device configuration of an application example in which the embodiment is adopted, and FIG. It is a line diagram which compares and shows the example of the latter data. P(k, ff1)...Pixel to be converted, 0 (a+
, n)... Original pixel, bo, bl, bz, b3... Combination operator 10... Pixel density conversion device, 12... Input image memory, (coefficient) 14... Operator table, 16. ...Relative position determination unit, 18...Product-sum calculation unit, 20...Output image memory.

Claims (2)

[Claims] (1) Image data formed at the first pixel density is transferred to the second pixel density.
In the pixel density conversion method for converting to pixel density data, the sharpening processing operator is configured to limit the original pixels referred to for sharpening processing to only the original pixels on the same line as the original pixels to be sharpened. A pixel density conversion method, comprising: configuring a combined operator that combines an operator for pixel density conversion processing and an operator for the sharpening process, and performing simultaneously pixel density conversion processing and sharpening processing using the combined operator. (2) Image data formed with the first pixel density is transferred to the second pixel density.
In a pixel density conversion device that converts pixel density data into pixel density data of an operator table stored in correspondence with the relative position; a relative position determining unit that determines the relative position of the pixel to be converted with respect to the original pixel position; reading out a combination operator corresponding to the relative position from the operator table; a product-sum operation unit that performs a product-sum operation on data of pixels to be converted, and the operator of the sharpening process selects an original pixel to be referred to for the sharpening process as an original pixel on the same line as the original pixel to be sharpened; A pixel density conversion device characterized in that it is configured to be limited to: