JP2949587B2 - Pixel density converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a pixel density conversion method and apparatus, and in particular,
The image data formed at the first pixel density, which can simultaneously perform the pixel density conversion and the sharpening of the image,
And a device for converting pixel density into pixel density data.

[Prior art]

For example, when an image input to an auxiliary storage device or the like at an appropriate resolution using a layout scanner or the like is output in a desired size by a hard copy device or the like having a different pixel density, such as a printer, the pixel density may be reduced. Must be converted and matched. Conventionally known as such a pixel density conversion method is a nearest neighbor method in which data of an original pixel closest to a pixel position to be converted is used as data of a pixel to be converted, The data of the pixels to be converted is obtained by linearly interpolating the data of the surrounding original pixels.
There are a linear method, a cubic convolution method, and the like, in which original pixel data surrounding a pixel to be converted is subjected to curve interpolation to obtain data of a pixel to be converted. On the other hand, in order to correct the characteristics of a hard copy device or the like or the sharpness of an image degraded by the pixel density conversion, an image sharpening process is required. Conventionally known as such a sharpening method is a method using a Laplacian which emphasizes a change in data by adding a second derivative of the data to the original data, or adding a correction to this Laplacian. There is a method using another differential operator.

[Problems to be solved by the invention]

However, conventionally, the pixel density conversion processing and the sharpening processing are performed independently of each other, and the image after the pixel density conversion is subjected to the sharpening processing, or conversely, the sharpening processing is performed. Since the pixel density of the subsequent image is converted, there is a problem that the processing time is longer than when only one of the processes is performed.

[Object of the invention]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional problems, and an object of the present invention is to provide a pixel density conversion method and apparatus capable of performing a pixel density conversion process and a sharpening process at high speed and with high accuracy. And

[Means for achieving the object]

The present invention relates to a pixel density conversion apparatus for converting image data formed at a first pixel density into second pixel density data, wherein a combined operator combining a pixel density conversion operator and a sharpening operator is provided. And storing a set of the combination operators for each of a plurality of partial regions, which are divided in correspondence with the relative positions of the pixels to be converted with respect to the positions of the original pixels surrounding the pixels to be converted. The above object has been achieved by simultaneously performing the pixel density conversion processing and the sharpening processing by the combination operator read according to the above. In a similar pixel density conversion device, a combination operator combining a pixel density conversion process operator and a sharpening process operator sets a relative position of a pixel to be converted relative to a position of an original pixel surrounding a pixel to be converted. An operator table stored for each of a plurality of partial areas correspondingly divided, a relative position determination unit for determining a relative position of a pixel to be converted with respect to the original pixel position, and a connection corresponding to the relative position The object is also achieved by including a product-sum operation unit that reads an operator from the operator table and performs a product-sum operation on data of pixels to be converted.

[Action]

According to the present invention, the sharpening process and the interpolation method, which is the essence of the pixel density conversion, have the same principle in terms of the filtering operation, and the pixel value of interest is calculated by the product-sum operation of the peripheral pixel values and the corresponding coefficients. Are calculated by paying attention to the fact that the calculation procedure of calculating That is, in the present invention, a combined operator is formed by combining an operator for pixel density conversion processing (set of product-sum coefficients) and an operator for sharpening processing.
By storing one set for each of a plurality of partial areas divided corresponding to the relative position of the pixel to be converted with respect to the position of the original pixel surrounding the pixel to be converted, both processes can be performed simultaneously. I have. Therefore, the pixel density conversion processing and the sharpening processing can be performed at high speed and with high accuracy.

【Example】

Hereinafter, with reference to the drawings, an embodiment of the present invention will be described in detail with reference to an example in which an image subjected to sharpening processing by a 3 × 3 operator is subjected to pixel density conversion by a bilinear method. FIG. 1 illustrates the principle of the present embodiment. Pixels to be converted are represented by P (k,
l), and as original pixels surrounding the pixel P (k, l) to be converted, a total of 16 original pixels (m, n), m = (i−
1, i, i + 1, i + 2), n = (j-1, j, j +
1, j + 2). Here, the pixel P to be converted
The horizontal component in the figure of the distance between (k, l) and the original pixel (i, j) is x, and the vertical component is y. Now, an intermediate pixel ′ obtained by subjecting the original pixel (i, j) to sharpening processing by nine 3 × 3 pixel operators around the original pixel (i, j)
The data (gradation value) of (i, j) is as shown by the following equation. '(I, j) = a ₀₀・ (i-1, j-1) + a ₀₁・ (i, j-1) + a ₀₂・ (i + 1, j-1) + a ₁₀・ (i-1, j) + a ₁₁ · (i, j) + a ₁₂ · (i + 1, j) + a ₂₀ · (i−1, j + 1) + a ₂₁ · (i, j + 1) + a ₂₂ · (i + 1, j + 1) (1) where coefficient a ₀₀ , a ₀₁ , a ₀₂ ,..., a ₂₂ are weighting coefficients corresponding to, for example, Laplacian. Similarly, the other original pixels (i + 1, j), (i,
j + 1), (i + 1, j + 1), and their surrounding 3
Intermediate pixel with sharpening process performed by × 3 operator
(I + 1, j), '(i, j + 1),' (i + 1,
j + 1) is obtained. Accordingly, the four intermediate pixels'
(I, j), '(i + 1, j),' (i, j +
1), '(i + 1, j + 1), for example,
The pixel density is converted by the linear method, and the pixels P (k,
In order to obtain the data (gradation value) of 1), a linear interpolation operation as in the following equation may be performed. P (k, l) = (1-y). {(1-x). '(I, j) + x.' (I + 1, j)} + y {(1-x). '(I, j + 1) + x '(I + 1, j + 1)｝ (2) By combining the above equations (1) and (2), the sharpening process and the pixel density conversion of the pixel P (k, l) to be converted are eventually performed. The data (gradation value) after the execution is expressed by the following equation. P (k, l) = b 00 · (i-1, j-1) + b 01 · (i, j-1) + b 02 · (i + 1, j-1) + b 03 · (i + 2, j-1) + b _{10 · (i-1, j} ) + b 11 · (i, j) + b 12 · (i + 1, j) + b 13 · (i + 2, j) + b 20 · (i-1, j + 1) + b 21 · (i, j + 1 _{) + b 22 · (i +} 1, j + 1) + b 23 · (i + 2, j + 1) + b 30 · (i-1, j + 2) + b 31 · (i, j + 2) + b 32 · (i + 1, j + 2) + b 33 · (i + 2, j + 2 ) (3) follow _{go-between, b 00, b 01, b} 02, ··· b 31, b 32, b 33 becomes 4
By using 16 × 4 operators, simultaneous processing of pixel density conversion and sharpening can be realized. In the above description, the same coefficient is obtained when performing the sharpening first and performing the pixel density conversion later. Conversely, the same coefficient as performing the pixel density conversion first and performing the sharpening later is obtained. Can be used. Although Laplacian is used for sharpening, other types of differential operators may be used. Further, as an interpolation method used for pixel density conversion, bi-
Although the linear method has been used, the operator may be configured using another interpolation method such as a nearest neighbor or a cubic convolution. FIG. 2 shows the configuration of an embodiment of the pixel density conversion device 10 for simultaneously performing the pixel density conversion and the sharpening process according to the above embodiment. In this embodiment, for example, using a layout scanner or the like,
An input image memory 12 in which data of original pixels formed at the first pixel density is stored, and a combination operator (b ₀₀ , b ₀₁ ,...) Combining a pixel density conversion processing operator and a sharpening processing operator B ₃₂ , b ₃₃ ) is the pixel P to be converted
An operator stored corresponding to a relative position (x, y) of a pixel to be converted with respect to a position of an original pixel (m, n) surrounding (k, l) and stored for each of a plurality of partial regions. A table 14 and a relative position determining unit 16 for determining a relative position (x, y) of a pixel to be converted with respect to the original pixel position;
The combination operator corresponding to the relative position (x, y) is read from the operator table 14, and the original pixel data (m, n) read from the input image memory 12 is used to obtain , Pixel data P to be converted
A product-sum operation unit for performing a product-sum operation on (k, l), and data of a pixel to be converted calculated by the product-sum operation unit,
It is configured to include an output image memory 20 provided for output of a printer or the like, a controller 24 for controlling the input image memory 12 and the output image memory 20 via the relative position determination unit 16 and the address calculation unit 22. . The operator table 14 has the 4 ×
The values of the four operators b ₀₀ , b ₀₁ ,..., B ₃₃ are stored. Since the values of the operators b ₀₀ , b ₀₁ ,..., B ₃₃ are uniquely determined by the combination of the relative positions x and y, several values including the pixel P (k, l) to be converted are included. By dividing the region surrounded by the pixel (m, n) into a plurality of partial regions with respect to the values of x and y, and limiting the operator value to each set for each partial region, This can be calculated in advance and stored in the operator table 14. For example, when the values of x and y are each limited to four, the result is as shown in FIG. Since the operators b ₀₀ , b ₀₁ ,..., B ₃₃ in the area surrounded by the broken line in FIG. 3 have the same value, the pixel P (k, l) to be converted and the neighboring pixels P (k, l)
Original pixels (i, j), (i + 1, j), (i,
Once the relative positions x and y with (j + 1) and (i + 1, j + 1) are obtained, it is determined which partial area the relative position belongs to, so that the operators b ₀₀ and b to be used in the calculation are calculated.
_01, ··· b ₃₃ is determined. In the case of this embodiment, there are 16 4 × 4 partial areas, and the operators b ₀₀ , b ₀₁ ,.
_Since there are also 16 sets of _33, they are stored in the operator table 14. Hereinafter, the operation of the embodiment will be described with reference to FIG. After the controller 24 determines the address of the pixel P (k, l) to be converted, the process proceeds to step S1, where the relative position determination unit 16 determines that the pixel P (k, l) to be converted is the pixel to be converted. Four original pixels (i, j) surrounding P (k, l),
(I + 1, j), (i, j + 1), (i + 1, j +
With respect to the position 1), an area determination as to which partial area is included is performed. Next, the process proceeds to step S2, and among the operators assigned to each of the partial areas, the operators b ₀₀ and b of the assigned partial area
_01, reads the ··· b _33. Then, the process proceeds to step S3, where the data (gradation value) of the pixel P (k, l) to be converted is calculated by the above equation (3) using the read coefficients. By repeating this for all the converted pixels, the tone value of each converted pixel is obtained, and the obtained tone value is stored in the output image memory 20. FIG. 5 shows a device configuration of an application example in which the pixel density conversion device 10 according to the present invention is adopted. In FIG. 5, high-density pixel data having a pixel density of about 12 to 20 lines / mm captured by a layout scanner 30 is transmitted via a controller 32 including the functions of the controller 24 (FIG. 2). Are stored in a memory 34 including the functions of the input image memory 12 and the output image memory 20 (FIG. 2). The pixel data stored in the memory 34 is supplied to the pixel density conversion device 10 according to the present invention via the controller 32, and the processing of the present invention is performed. According to the pixel density (usually lower than the input data) of the hard copy device such as a printer, the data after the pixel density conversion and the sharpening process as shown in FIG. The data is read and provided to a hard copy device such as a printer. In the present embodiment, when storing the operator table 14, the area including the pixel P (k, l) to be converted and surrounded by the four original pixels (m, n) is 4 × 4.
It is divided into 16 partial areas, and a coefficient b ₀₀ ,
Since a set of b ₀₁ ,..., b ₃₃ is determined and stored, the corresponding coefficient can be quickly read out from the operator table, and hardware implementation is easy. Note that the number of original pixels including the pixel to be converted and the number of partial regions are not limited thereto. Further, in the above-described embodiment, the combination operator is configured using 16 coefficients of 4 × 4, but the number of coefficients configuring the combination operator is not limited to this.

As described above, according to the present invention, the sharpening process is performed by the sum-of-products operation of the combination operator obtained by combining the operator of the sharpening process and the operator of the pixel density conversion process with the original pixel operator. Pixel density conversion processing can be performed simultaneously. Therefore, there is an excellent effect that both processes can be performed at high speed and with high accuracy in substantially the same time as one of the processes.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relative positional relationship between a pixel to be converted and an original pixel for explaining the principle of an embodiment of a pixel density conversion method according to the present invention, and FIG. A block diagram showing the configuration of an embodiment of the adopted pixel density conversion device;
FIG. 3 is a diagram showing a relative positional relationship between a pixel to be converted and an original pixel and a partial area for explaining a state of data stored in an operator table used in the embodiment; FIG. 4 is a flowchart showing the processing procedure of the above-mentioned embodiment, and FIG. 5 shows an apparatus configuration of an application example in which the above-mentioned embodiment is adopted. FIG. 6 is a diagram showing a comparison between examples of data before and after processing according to the present invention. P (k, l): pixel to be converted, (m, n): original pixel, b ₀₀ , b ₀₁ ,..., B ₃₃ … combination operator (coefficient), 10: pixel density conversion device, 12: Input image memory, 14: Operator table, 16: Relative position determination unit, 18: Product-sum operation unit, 20: Output image memory.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/387-1/393

Claims (1)

(57) [Claims] 1. A pixel density conversion apparatus for converting image data formed at a first pixel density into second pixel density data, wherein a combination of a pixel density conversion operator and a sharpening operator is combined. An operator table divided by the operator corresponding to the relative position of the pixel to be converted with respect to the position of the original pixel surrounding the pixel to be converted, and stored in a set for each of a plurality of partial areas; A relative position determination unit that determines a relative position of a pixel to be converted; and a product-sum operation unit that reads a joint operator corresponding to the relative position from the operator table and performs a product-sum operation on data of the pixel to be converted. A pixel density conversion device characterized by including: