JP2798541B2 - Image data processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data processing apparatus, and more particularly, to an image data processing apparatus which handles a grayscale image as binary image data.

[0002]

2. Description of the Related Art Conventionally, this type of image data processing apparatus has
Each pixel constituting the grayscale image is read based on one predetermined grayscale threshold value, and binary image data indicating grayscale is generated. The binary image data generated in this manner is processed for visual display as a grayscale image of (M × N11) gradations in units of a predetermined number of (M × N) pixels vertically and horizontally adjacent to each other. Is done. FIG. 3 shows an example of a gray-scale image in which binary image data is processed in units of 2 × 2 pixels and represented by five gradations of 30 to 34.

[0003]

In the above-described conventional image data processing apparatus, since the density of an image is expressed in M × N pixels, the resolution of the image is reduced to 1 / (M × N) times. That is, the screen at the time of the visible display becomes coarser.

[0004]

According to the present invention, there is provided an image data processing apparatus for converting image data of an image composed of a plurality of pixels into a level based on a plurality of thresholds predetermined according to the number of gradations. First means for converting a plurality of sets of binary image data by comparison; second means for storing the plurality of sets of binary image data for each of the sets; and the binary image stored for each of the sets Third means for generating, for each of the plurality of pixels, grayscale information indicating the degree of the grayscale based on a binary value of the data at the same pixel position.

[0005]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an image data processing apparatus according to one embodiment of the present invention. FIG. 2 shows an example of image data processing in the embodiment.

In this embodiment, image data 20 is represented by four gradations, and three thresholds I1, I2 and I3 are set. The first threshold value I1 is a value for determining a pixel having a density lower than the highest density to be "0" and determining a pixel having the highest density to be "1". The second threshold value I2 is a value for determining a pixel having a density lower than the second highest density to be “0”, and determining a pixel having the same density as or higher than the second highest density to be “1”. The third threshold value I3 is a value for determining a pixel having a density lower than the third highest density to be "0" and determining a pixel having the same or higher density as the third highest density to be "1". In FIG. 2, the image data 20 and three thresholds I1, I2
Although the density difference of the diagonal lines is used to represent the density with I3 and I3, the actual density image is represented by the density difference. Further, in FIG. 2, pixel names a, b,..., K, l are assigned to respective pixels of the image data 20.

The binary image input unit 1 converts the image data 20 into "1" and "0" based on (the number of gradations-1) different thresholds In (here, three thresholds I1, I2 and I3). Read to determine. 2 generated by this determination
The value image data Dn (n = 1, 2, 3) is stored in the binary image data storage unit 2. Here, Dn represents binary image data read at the n-th threshold shading level, and the density indicated by the threshold is lighter in proportion to the increase in n. Therefore,
The binary image input unit 1 makes a “1” or “0” determination on the image data 20 with reference to the threshold value I1, generates binary image data D1, and supplies the binary image data D1 to the binary image data storage unit 2. Similarly,
The binary image input unit 1 converts the image data 20 into threshold values I2 and I3.
Are determined as "1" and "0" based on each of the above, binary image data D2 and D3 are generated and supplied to the binary image data storage unit 2, respectively. As described above, since the binary image data D1 represents the determination result of “1” and “0” of each pixel of the image data 20 based on the threshold I1, the pixels a, b, and
1, 0, 0,... corresponding to c,.
1,0. Similarly, the binary image data D2 has a threshold value I2
Represents the determination results of “1” and “0” on the basis of “1”, “1” and “1” corresponding to the pixels a, b, c,.
0, ..., 1,1. Similarly, the binary image data D3 corresponds to pixels a, b, c,.
1,1,..., 1,1. The binary image data storage unit 2 stores the binary image data D1 and D2 from the binary image input unit 1.
Each of 2 and D3 is stored in units.

The pixel density calculation unit 3 generates binary image data Dn by reading each pixel with reference to the n-th threshold value In, and when the data Dn changes from "0" to "1", n Is set in the grayscale data T as the grayscale value of the pixel. The higher the number of the gray value, the lighter the density.
By performing this processing on the binary image data D1, D2, and D3, the pixel “a”
1 ", the gray value 1 is obtained, and the pixel b is" 1 "in the binary image data D2.
Is "1" in the binary image data D3, so that the gray value 3 is obtained. Since the binary image data D1, D2, and D3 are all "0", the gray value 4 is obtained. By performing the same processing from the pixel e to the pixel 1, the grayscale data T of 1, 2, 3,..., 1 and 2 corresponding to the pixels a, b, c,. The pixel density calculation unit 3 stores the density data T in the multi-tone image data storage unit 4. The image display unit 5 visually displays the grayscale value of each pixel of the grayscale data T stored in the multi-tone image data storage unit 4 as the brightness of the display pixel.

In this embodiment, three thresholds I1 and I
Although 2 and I3 are set, the number of thresholds is determined according to the number of gradations.

[0011]

As described above, according to the present invention,
A plurality of sets of binary images are determined by determining "0" and "1" for image data corresponding to an image composed of a plurality of pixels with reference to each of a plurality of predetermined thresholds according to the number of gradations. The plurality of sets of binary image data are respectively stored, and based on the values of "0" and "1" at the same pixel position of the plurality of sets of binary image data, the gradation corresponding to the number of gradations is obtained. Since the grayscale information of each of the plurality of pixels indicating the degree is generated for visible display, it is possible to perform visible display at the same resolution as the image data before conversion to the image data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an image data processing device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of image data processing in the embodiment.

FIG. 3 is a diagram for explaining conventional image data processing.

[Explanation of symbols]

 Reference Signs List 1 binary image input unit 2 binary image data storage unit 3 pixel density calculation unit 4 multi-tone image data storage unit 5 image display unit 20 image data D1 to D3 binary image data T density data

Continuation of front page (58) Fields investigated (Int.Cl. ⁶ , DB name) H04N 1/40-1/409 G06T 5/00

Claims (2)

(57) [Claims] 1. A method of converting image data of an image composed of a plurality of pixels into a plurality of sets of binary image data by level comparison based on a plurality of thresholds predetermined according to the number of gradations. Means for storing the plurality of sets of binary image data for each set; and means for storing the plurality of sets of binary image data for each set based on binary values at the same pixel position of the binary image data stored for each set. An image data processing apparatus, comprising: third means for generating density information indicating a degree of density for each of the plurality of pixels. 2. A method according to claim 1, further comprising: fourth means for storing the grayscale information generated by the third means; and fifth means for visually displaying the grayscale information described in the fourth means. The image data processing apparatus according to claim 1, wherein: