JPH02101870A - Picture element density converter and its method - Google Patents

Abstract

PURPOSE:To minimize number of multiplication circuits by selecting an area ratio W to be one over power of (n) when conversion such as magnification or reduction is applied to a picture element density of a multi-value picture and attaining a product IXW between the ratio W and each density I of a picture element to be converted required to calculate the density of the conversion picture element with bit shift or carry down only. CONSTITUTION:In the case of detecting the density of a conversion picture element, a converted picture element input means 1 such as a transmission means is used to read a picture to be converted and a density data of the picture element to be converted located near the present conversion picture element is inputted. Then the density data is inputted to multiplexers 131-134 and a split area ressesing circuit 12 as a split area decision means 2 in this case decides the split area in which the conversion picture element belongs based on conversion magnification p, q on the converted picture element plane of the present conversion picture element. Then 2-bit information required to apply digit shift by a decoder of the multiplexer 131-134 receiving the split area information is generated and digit shift or operation is implemented based on the split area decided by the circuit 12.

Description

[Detailed description of the invention] [Table of contents] Overview Background of the industrial application field technology (Fig. 10) Conventional technology (Fig. 10.11) Problems to be solved by the invention (Figs. 12 to 14) Means for solving the problem (Figures 1 and 2) Effect (Chapter 1.2.
(Figure 10) Embodiment (Figures 3 to 10) Effects of the invention (Summary) Each pixel is divided from the density of neighboring pixels to be converted according to the divided area in which the converted pixel projected onto the plane in which the pixels to be converted are arranged is located. Regarding a pixel density conversion device and method for determining the density of converted pixels by a projection method, it is possible to minimize arithmetic operations, achieve high-speed processing with a small-scale circuit configuration, and obtain a smoothed image when enlarged. With the aim of A divided area is set based on the assumption that within that area, each density of the converted pixel group contributes to the density of the converted pixel by each area ratio having a size of - the corresponding power of n. It is determined in which divided area the converted pixel is located, and based on the determined divided area, each density data of the converted pixel displayed in the n-ary system is shifted by digits, and each converted pixel that has been digit shifted is The configuration is such that the density of the converted pixel is calculated from the density data of .

[Industrial application field]

The present invention relates to a pixel density conversion device and method, and more particularly, the present invention relates to a pixel density conversion device and method, and in particular, the density of each converted pixel is calculated from the density of neighboring converted pixels according to the divided area in which the converted pixel is located, which is projected onto a plane on which the converted pixels are arranged. The present invention relates to a pixel density conversion device and method determined by a projection method.

[Technology background]

Current image processing systems often target not only black-and-white binary images but also multi-value images such as half-tone and full-color images, and enlargement/reduction techniques are indispensable when editing multi-value images. Halftone and full-color scanners and printers (thermal transfer, electrophotography) are also beginning to become popular among image input/output devices, and pixel density conversion devices play an important role between devices with different resolutions.

Now, a pixel density conversion device (image enlargement,
The projection method used as (reduction) is a method of determining the density from the last four pixels of the tube and the adjacent converted pixels to the converted pixel (Journal of the Institute of Image Electronics Engineers, Vol. 11, No. 2, 72-8)
3.1982).

FIG. 10 shows the principle of the projection method. Geometric mode conversion 1
In the projection method, first, the neighboring four pixels A, B, C, D
Divide the transformed image plane containing into four equal parts. Let the densities of four neighboring pixels be IA, IB, IC, and ID, and when the converted pixel R is projected onto the pixel surface to be converted, the area ratios projected onto the quadrants are WA and WB.

We, Wo.

Then, the density of the converted pixel R is l n mΣi, * Wt; i=A, B, C, D
”” Determined by *.

Here, it is generally ΣWz-1.

Note that p and q in FIG. 10 are conversion magnifications in the X-axis and Y-axis directions.

(Prior Art) Conventionally, there has been a pixel density conversion device shown in FIG. 11 when the density of a converted pixel is determined by a projection method for pixel density conversion.

In this example, as shown in FIG. 10, the density data IA, In, Ic of the converted pixels located in the four converted pixels A, B, C, and D shown in FIG. A means for inputting In (not shown), an area ratio calculation circuit 112 for calculating the area ratio where the current converted pixel is located, and each area ratio WA, Wa, We obtained by the circuit 112.
, Wn and four converted pixels A located near the converted pixel.

It has a multiplication means 113 that multiplies B, C, and D by the density data IA=IB, IC, and ID, and an arithmetic means 114 that adds the multiplication results and outputs the density of the converted pixel. .

Furthermore, the multiplication means 113 is a multiplier 113a.

113b, 113c, and 113d, and the calculation means 1
Reference numeral 14 denotes an adder 114a that adds the multiplication results of the multipliers 113a and 113b, an adder 114b that adds the multiplication results of the multipliers 113c and 113d, and the adder 1.
Adder 114 that adds the addition results of 14a and 114b
It has C.

Further, the area ratio calculation circuit 112 calculates (0,5+px)*(0,5+qy) from the values of the position coordinates X and Y of the converted pixel, the sign between them, and the conversion magnification p and q, and calculates each area ratio. Find WA, WB, We, and Wo. Then, the multipliers 113a, 113b, 113c.

Reference numeral 113d indicates density data IA, In, rC, rD of the four pixels A, B, C, and D input from the pixel input means (not shown) and the area ratios WA, W.
a, We −Wo, and the operator stage 114
adder i 14a, 114b.

114c, and the density of the converted pixel is obtained according to the above formula*.

Therefore, in the entire circuit of Fig. 11, the multiplication is 3 x 4 + 4-1.
6 times, addition and subtraction will be performed 2X 4+3-11 times.

(Problem to be solved by the invention) By the way, conventionally, when converting pixels,
When calculating the density of the l-converted pixel, if sequential processing were performed, 27 (-11+16) arithmetic operations would be required as described above, making it impossible to perform high-speed calculations.

In addition, when performing parallel processing, a Vibrine configuration must be adopted in which 16 multiplication circuits are used alone, resulting in a problem that the circuit scale becomes enormous.

In addition, in the conventional projection method, as shown in Fig. 12, in the case of reduction, most of the density of the converted pixel R is determined by the area ratio of the surrounding four converted pixels; The density differs slightly, and the block shape indicating the shape of the pixel to be converted cannot be determined. However, as shown in FIG. 13, in the case of enlargement, there are many parts where the density of the converted pixel R is determined by the density of one converted pixel.
As shown in the 5 times enlarged example of FIG. 4, the block shape representing the shape of the pixel to be converted stands out clearly, which has the problem of degrading the image quality.

Therefore, the technical object of the present invention is to solve the above problems, and by minimizing the number of arithmetic operations, especially the number of multiplication operations, high-speed processing can be achieved with a small-scale circuit configuration. The purpose of this invention is to provide an apparatus and method for converting pixel density of a multivalued image.

(Means for Solving the Problems) In order to solve the above technical problems, the first invention provides a divided area in which converted pixels are located, projected onto a plane in which converted pixels are arranged, as shown in FIG. In a multivalued pixel density conversion device that determines the density of each converted pixel from the density of neighboring converted pixels according to the projection method, a predetermined group of converted pixels expressed in an n-ary system located in the vicinity of the converted pixel. Based on the converted pixel input means 1 which inputs the density data of the converted pixel group, the conversion magnification during reduction or the fixed conversion magnification during enlargement, and the arrangement of the converted pixels, Assuming that each density contributes to the density of the converted pixel by each area ratio having a size of 1 to the power of the corresponding n, determine in which divided area of the set divided areas the converted pixel is located. divided area determining means 2 for determining, and digit shifting means 31 and 32 for shifting the digits of each density data of the converted pixel displayed in the n-ary system based on the divided area determined by the determining means 2; . . 3 m, and an arithmetic means 4 for calculating the density of the converted pixel from the density data of each converted pixel shifted by the digits by the digit shifting means 31, 32° . . . 3 m.

On the other hand, the second invention, as shown in FIG. 2, calculates the density of each converted pixel from the density of neighboring converted pixels according to the divided area in which the converted pixel is projected onto the plane on which the converted pixels are arranged. In a pixel density conversion method that determines by a projection method,
A process (S1) of sequentially inputting density data of a predetermined group of converted pixels located in the vicinity of a converted pixel and displayed in n-ary system, a conversion magnification at the time of reduction or a fixed conversion magnification at the time of expansion, and Based on the array of converted pixels, assume that within that region, each density of the converted pixel group contributes to the density of the converted pixel by each area ratio having a size of one part of the corresponding power of n. , a step (S2) of determining in which divided region of the set divided regions the converted pixel is located; A process (S3) of digit shifting the density data of each pixel to be converted, and a process (S4) of calculating the density of the converted pixel from the density data of each pixel to be converted, which has been digit-shifted by the digit shifting process (S3).
).

[Effect]

A detailed explanation of the first and second inventions will be given.

When converting the pixel density of a multivalued image according to the present invention, as shown in FIGS. Based on the position projected onto the plane, the converted pixel input means l selects the n-ary system (
The density data of each pixel to be converted, expressed in a binary system in most cases, is sequentially input to the pixel conversion device. Here, "converted pixels located in the vicinity" means, for example, A, B, C, D surrounding the converted pixel as shown in FIG.
There are 4 pixels.

In step S2, the divided area determination means 2 determines the divided area in which the converted pixel is located.

Here, the "divided area" refers to the reduction of pixel density conversion.
That is, when the conversion magnification is 1 or less, it is based on the conversion magnification and the array of pixels to be converted, and in the case of expansion, that is, when the conversion magnification is 1 or more, it is fixed regardless of the conversion magnification. Based on a predetermined conversion magnification and the arrangement of pixels to be converted, within that area, the density of the converted pixel is determined by an area ratio having a negative size of the width (power) of n for each density of the group of pixels to be converted. This is an area set as contributing.

Further, the "predetermined conversion magnification" is an appropriate conversion magnification at the time of enlargement, and for example, a conversion magnification of 1, which is the lowest at the time of enlargement, is used. The reason why the conversion magnification is fixed during enlargement is to simplify the processing and smooth the diagonal parts.The reason why the conversion magnification is kept as small as possible is because the divided area becomes smaller as the conversion magnification increases. This is because the image may become rough.

Furthermore, "contributing" is not necessarily limited to contributing by an accurate area ratio determined by the position of the converted pixel, but may be treated as contributing if a certain degree of contribution tendency is taken into account. .

The influence of the density of a pixel to be converted on the density of a certain converted pixel is given by the above-mentioned formula*.

Furthermore, as mentioned above, the "area ratio" means, for example, when the nearby converted pixels are A, B, C, and D, the density of each converted pixel is ■. ,
1. , lc, I. WA, Wa expressed as a coefficient of
, We, and WD.

In step S3, the divided area determining means 2 makes a determination and gives a digit moving instruction to the digit moving means 31, . . . , 3m based on the divided area.

Here, m indicates the number of converted pixels located in the vicinity of the converted pixel, and is usually m=4, for example.

That is, each digit moving means 31. ...3m is provided for each pixel to be converted located in the vicinity of the pixel to be converted, and digits are shifted independently for each pixel to be converted based on the divided area in which the pixel to be converted is located. That will happen.

This is because, as mentioned above, the influence of the density of each converted pixel on the density of the converted pixel is made to correspond to each divided area by the area ratio carved by the power of n, so calculations such as multiplication are performed. This is because the influence from each pixel to be converted can be obtained only by shifting the digits.

In step S4, the calculating means 4 can calculate the density of the target conversion pixel based on the influence of the density obtained for each pixel to be converted.

For example, when the density of the converted pixel is calculated based on the above-mentioned formula*, only addition is required, and the calculation is greatly simplified.

〔Example〕

Next, examples of the present invention will be described.

FIG. 3 shows a pixel conversion device according to this example.

As shown in the figure, this example is located near a predetermined converted pixel read out by a converted pixel input means such as a camera that reads directly from the original image, or a transmission means that transmits data from a host computer, etc. 4 pixels A and B as shown in FIG.

Each density data IA, I, 1 . ,1. Digit shift means 31.3 that inputs and performs digit shift (bit shift) on the concentration data.
4→1 multiplexer 131 as 2,33.34,
132, 133, 134, and an area determination circuit 1 that determines the divided area to which the currently targeted converted pixel belongs.
2, and an arithmetic circuit 14 as the arithmetic means 4 that outputs the density IR of the converted pixel.

The area determination circuit 12 uses the coordinates X, Y of the converted pixel and the conversion magnification p, q to determine the divided area set according to FIG. 5 and Table 1 in the case of enlargement, and according to FIG. 6 and Table 2 in the case of reduction. Determine the area.

The arithmetic circuit 14 includes the 4→1 multiplexer 131.
Addition fll that adds the digit shift results from 132,
14a and the 4→1 multiplexer 133.134
an adder 14b that adds the movement results of , and the adder 1
Adder 14c that adds together the addition results of 4a and 14b.
and has.

Here, the density of the pixel to be converted is not simply binary data representing black or white, but is intended for multivalued images such as halftones and full color, and each density is expressed with 4 bits. It is assumed that

FIG. 4 shows the multiplexer 131 in detail.

The multiplexer 131 inputs each digit IAO+IA of the multilevel density data displayed in 4 bits of the input pixel to be converted.
The multiplexers 131a, 131b, 131c, and 131d are provided for each I*IA2+I, 3, and each multiplexer 1 is selected based on the divided area in which the current converted pixel sent from the divided area determination circuit 12 is located.
31a, b, c, and d.

When the coordinates of the converted pixel are (x, y), in the case of enlargement (conversion magnification is 1 or more) in divided area group 1 in Fig. 5, each divided area is divided by the following straight lines. ing.

Note that here it is assumed that X)0 and Y)0. Also,
In order to simplify the curve of the above-mentioned formula* into a straight line and smooth the oblique portion, p and q in the formula* are each fixed to 1. (This is because if p and q are set large, the divided area itself becomes smaller and the image becomes rougher.) In divided area group 1 shown in Figure 5, when the coordinates of the converted pixel are (x, y), (Straight line X+Y)O-75: Region G3 If the area ratio exceeds wc-0, 75, it is approximately expressed as Wc-t using only Ic.

■ Straight line X+Y (0,33: Area G13 area ratio Wc-
WA if it does not exceed 0.33.

Expressed as an equal combination of Wa, We, and Wo J/4.

■ Straight line 0.33(X+Y(0,75: area G9,
Assuming GIOWe = 1/2, select the second closest pixel using the following formula and calculate W? -1/4.

(i) Straight line Y)X: Area G9 WA-1/8. Wa -1/4. We -1/2.
Expressed by Wn 178.

(if) Straight line Y (X: area GIO WA=178, W!I”1/8. We −17
2, expressed as Wn ``1/4.

Furthermore, divided region group 2 in the case of reduction in FIG. 6 is divided by the following straight lines.

Note that here it is assumed that X)O and Y)0. Also, although the curve in formula * is simplified to a straight line, in the case of reduction,
Since the information of multiple pixels must be collected into one converted pixel according to the magnification, the values of p and q are used as they are.

■ Straight line 1)
Approximately expressed by only.

■ pX+qY <0,33: Area G13 area ratio W
. -WA if it does not exceed 0.33.

Expressed as an equal combination of Wa, We, and Wn''1/4.

■ 0.33 (pX+qY<0.75: area G9,
Assuming the GIO area ratio We·1/2, the second closest pixel is selected using the following formula, and Wy = 1/4.

(i) Straight line Y)X: Area G9 WA -1/8. WB-1/4, Wc-1/2
, expressed by WD-1/8.

(ii) Straight line Y (X: area G10 WA "1/8. WB-1/8, Wc"
It is expressed by 1/2 and Wo-1/4.

Next, the operation of this embodiment will be explained.

When calculating the density of a converted pixel according to this embodiment, the converted image is read by the converted pixel input means such as the transmission means, and the density data of the converted pixel located in the vicinity of the current converted pixel is input. .

The input density data of each pixel to be converted is input to the multiplexers 131, 132, 133, and 134.

At this time, the divided area determination circuit 12 as the divided area determining means 2 determines the divided area to which the converted pixel belongs based on the position of the current converted pixel on the converted pixel plane and the conversion magnifications p and q. I will do it.

In this example, as shown in FIG. 5, in the case of enlargement processing based on the conversion magnifications p and q, divided area group 1 is set, and the judgment for each divided area is performed based on the conditions shown in Table 1. Become.

Table 1 Division conditions in Figure 5 (enlarged) Note 1) For areas on the boundary line, select one from multiple areas.

Note 2) If the expansion/reduction conditions for the conversion magnifications p and q are different, select either the divided area in Figure 5 or Figure 6.

Furthermore, as shown in FIG. 6, in the case of reduction processing, a divided region group 2 is set based on the conversion magnifications p and q, and the determination of divided regions is performed based on Table 2.

Table 2. Dividing conditions (reduction) in Figure 6 Note 1) For areas on the boundary line, select one from multiple areas.

Note 2) If the expansion/reduction conditions for conversion magnifications p and q are different, select either the divided area shown in Figure 5 or TS6.

Steps SR71 to 5R85 in FIG. 7 are based on divided region group 1 in FIG. 5, and step 5R9 in FIG.
0 to Step 5R104 shows the flow of the processing procedure when the divided area determination circuit 12 makes a determination based on the divided area group 2 of FIG. For example, in FIG. 7, the divided area determination circuit 12 determines whether X≧0 (step 5R71) and Y≧0 (steps 5R72, 73).
), x+y ≧o, 7s (step S R74
~77'), whether x+y ≧0.33 (steps 5R78 to 81), and whether Y≧x (steps 5R82 to
85), it is easy to determine which divided area the current converted pixel belongs to.

Note that the signs of X and Y regarding whether X+Y≧0.75, x+y≧0.33, and Y≧x depend on the signs of whether X≧0 or not and Y≧0.

In this way, information regarding the divided area to which the current converted pixel belongs is transmitted to the multiplexer 131, 132, 133,
134 as 4-bit information.

The multiplexer 131 that received the divided area information
, 132, 133, 134 decoder 131e (132
e, 133e, 134e) are converted into 2-bit information (information specifying 0.1 and 2.3 of each multiplexer) necessary to perform the corresponding digit shift based on the divided area. Multiplexer 131a, 131b, 1
31c131d, etc.

The multiplexers 131, 132, 133° 134 and the arithmetic circuit 14 shift digits based on the divided area determined by the divided area determination circuit 12 in order to obtain the density corresponding to the current converted pixel from the density data of the converted pixel. Or it is something that performs calculations.

Table 3 shows, for each divided area, the 2 densities to which each pixel group to be converted corresponds when the current converted pixel is located in the divided area.
The contribution to the density of the converted pixel is described through each area ratio having a magnitude of - to the power of .

In other words, each area ratio WA, Wa of the above formula*
, Wc, and Wo are expressed as - to the power of 2, and the density of each converted pixel located in each divided area is described.

Table 3. In other words, when the current converted pixel belongs to the divided regions Gl, G2, G3, G4, the arithmetic operation formula according to the embodiment is determined by the divided region determination circuit 12. It is sufficient to consider the influence of only the converted pixels A, B, C, and D.

Therefore, when the current converted pixel belongs to the divided area G1, the decoder 131e of the multiplexer 131 shown in FIG.
A signal to select "3" is sent to 1b, 131c, and 131d so that no digit shift is performed.

Furthermore, when it is determined that the current converted pixel belongs to divided area 05, as is clear from Table 3, the contribution from the density of pixel A to the density of the converted pixel is on the order of 1/2. Therefore, it is sufficient to shift the density data (expressed in binary) of the pixel A by one digit.

Therefore, the decoder 13 of the multiplexer 131
1e is each multiplexer 131a, 131b, 131c
, 131d, it is sufficient to select 412+#.

In addition, as is clear from Table 3, the multiplexer 1
31 outputs 0"' without making any selection when the divided area is 02, G3, or G4, and when the divided area is 06, in FIG. , if the divided area is G7, G12°G13, select "1" in Fig. 4 (1/4 contribution), and if the divided area is G
8, G9, GIO.

In the case of Gll, "0'' is selected in FIG.

Thus, the multiplexer 131°132.133
.
is added to obtain the density of the current converted pixel.

As explained above, in this embodiment, when determining a region in the divided region determination circuit 12, one addition is required in the case of enlargement and three times of comparison, and one addition is required in the case of reduction. , two multiplications, and three comparisons are required. In addition, addition is required three times in the arithmetic circuit 14, and adding four selections in the multiplexer results in 10 to 12
This means that the number of operations required is significantly reduced compared to the conventional method (27 operations). In particular, since the number of multiplications is small, the circuit scale can be made small (compact).

(Effects of the Invention) As explained above, in the present invention, when converting (enlargement, reduction) the pixel density of a multivalued image, the area ratio W is reduced to the power of n (in most cases, 2). By setting -, the multiplication I*W of each density I and W of the converted pixel, which is necessary when calculating the density of the converted pixel, is performed only by bit shifting or downshifting, and the number of multiplication circuits is minimized. be able to.

Therefore, it is possible to realize dramatically high-speed processing with a small-scale circuit.

Furthermore, when enlarging, by keeping the divided areas constant regardless of the conversion magnification, changes in density in diagonal directions are smoothed, and for example, as shown in Fig. 9, a smooth image with inconspicuous block shapes can be obtained. Can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the first invention, FIG. 2 is a flowchart of the principle of the second invention, and FIG. 3 is a block diagram of the embodiment.
FIG. 4 shows a 4→1 multiplexer circuit that shifts the density IA (4 bits) of the pixel to be converted based on Table 3, and FIG. 5 shows divided area group 1 during enlargement according to the embodiment. , FIG. 6 is a diagram showing divided region group 2 during reduction according to the embodiment, FIG. 7 is a flowchart (enlarged) showing the region determination processing procedure of FIG. 5, and FIG. 8 is a diagram showing the region determination process of FIG. 6. Flowchart showing the processing procedure (reduced), Figure 9 is a diagram showing an example of 5 times enlargement according to the embodiment, Figure 10 is a diagram showing the relationship between the position of the converted pixel and the area ratio in the projection method, and Figure 11 is the conventional Block diagram according to an example,
Fig. 12 is a diagram showing the area ratio in the case of reduction in the projection method, Fig. 13 is a diagram showing the area ratio in the case of enlargement in the projection method, and Fig. 14 is a diagram showing an example of 5 times enlargement according to the conventional example. . 1... Converted pixel input means 2 (12)... Divided area determination means (divided area determination circuit) 31-3m (131-134)... Digit moving means (4→
1 multiplexer)

Claims (2)

[Claims] (1) In a pixel density conversion device that uses a projection method to determine the density of each converted pixel from the density of neighboring converted pixels according to the divided area in which the converted pixel is located, projected onto a plane on which the converted pixels are arranged. , a converted pixel input means (1) for inputting density data of a predetermined group of converted pixels expressed in an n-ary system located in the vicinity of the converted pixel; and a conversion magnification during reduction or a fixed conversion during enlargement. Based on the magnification and the arrangement of the pixels to be converted, each density of the group of pixels to be converted within that area is determined by the density of the converted pixels according to each area ratio having a size of one part to the corresponding power of n. a divided area determining means (2) that determines in which divided area of the set divided areas the converted pixel is located in order to contribute to the divided area; and n based on the divided area determined by the determining means (2). A digit moving means (31, 32..., 3m) that moves the digits of each density data of the pixel to be converted that is displayed in a base system, and each digit moving means (31, 32..., 3m) A pixel density conversion device comprising: calculation means (4) for calculating the density of each converted pixel from the density data of each converted pixel shifted by digits. (2) In a pixel density conversion method in which the density of each converted pixel is determined by a projection method from the density of neighboring converted pixels according to the divided area in which the converted pixel is located projected onto a plane on which the converted pixels are arranged, A process (S1) of sequentially inputting the density data of a predetermined group of converted pixels located in the vicinity of the converted pixel and displayed in n-ary system; Based on the array of converted pixels, assume that within that region, each density of the converted pixel group contributes to the density of the converted pixel by each area ratio having a size of one part of the corresponding power of n. , a step (S2) of determining in which divided region of the set divided regions the converted pixel is located; The step of shifting the digits of each density data of the pixel to be converted (S3), and the step of shifting the digits (S3)
) A method for converting a pixel density of a multivalued image, comprising the step of calculating the density of each converted pixel from the density data of each converted pixel shifted by digits (S4).