JPS5860878A - Picture recording device - Google Patents

Abstract

PURPOSE:To improve an apparatus resolution by making a maximum gradation difference between respective dots in one picture element or picture elements in one group less than the gradation difference between the highest gradation level and lowest gradation level, and smoothing the presentation of a color grade table. CONSTITUTION:The upper half data of picture elements are supplied to a decoder 1 and exploded according to the gradations that the data represents. For example, when the data has a gradation[5], the decoder 1 outputs a signal from its terminal 5. At this time, an up/down control signal shows[up]and a frequency control signal has a level[H], so outputs from AND gates AG1 and AG5 are inputted to a buffer memory 2 through OR gates OG8 and OG9 to perform the 1st printing. Then, the same data is supplied to the decoder 1 and the frequency control signal goes down to[L], so only the AND gate AG6 is opened to print the right upper dot again. Thus, a print having a right black and a left half-tone part is obtained. Similarly, the lower half part of picture elements is printed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image recording device that receives an image signal and creates a hard copy, and is particularly suitable for use in a device that creates images with gradation.

The following is known as a conventional gradation recording method for this type of apparatus.

(1) A method of expressing gradation by adding shading to each pixel according to the gradation.

(A method in which each pixel is composed of a plurality of dots, the number of printed dots is controlled according to the gradation, and the gradation is expressed by the dot density in each pixel.

(3) A method using the dither method.

<41. A method that reduces the number of dots constituting one pixel by using a combination of (1) and (2) to introduce a gradation expression method that adds shading to the gradation expression method based on dot density.

In the method (1), the gradation level is easily affected by the nonlinear characteristics of the printing means, the nonlinear characteristics of the color development of the recording paper, and variations in the characteristics of these printing means or the recording paper.
This is extremely disadvantageous in terms of stability, reproducibility, etc. in practice.

In method (2), I! Conceptual diagram of printing in Figures 1 and 2 (
As shown in the case where one pixel is composed of 4 dots and 9 dots, respectively, gradation is expressed by the number of colored dots in one pixel, but as the number of gradations increases, both sides of one pixel become thicker ( ,
It has the disadvantage that the resolution decreases.

In the method (3), the resolution does not decrease as in the method (2), but when the number of gradations is increased, the resolution tends to decrease as well. The deterioration of resolution is particularly noticeable in image areas where the immersion is weak.

The method (4) is disclosed in Japanese Patent Publication No. 19836/1983, and for example, even if one pixel is composed of 4 dots as shown in the printing conceptual diagram in Fig. 3, 9 gradations can be achieved. I can express it. Therefore, a multi-tone image can be formed without increasing the area of one pixel. However, since a gradation factor based on dot density is introduced, some influence on resolution cannot be avoided. Furthermore, the difference in gradation between any two adjacent dots in one pixel is large, and white and black patterns coexist, resulting in an image that lacks smoothness and an apparent reduction in resolution.

In view of the problems of the above-mentioned methods, the present invention is intended to suppress a decrease in resolution and realize stable and smooth gradation expression.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a conceptual diagram of printing showing the first embodiment of the present invention. The T print pattern shown in Figure lI4 can be printed with a thermal printer using a heat-generating head and thermal paper, and is composed of dots with maximum density color (cross-hatching area). The gradation difference between is always 1
The pattern is determined so that the lowest level (no color) dots and the highest density dots (gradation difference 2) do not coexist.

FIG. 1I5 is a power supply time chart of the heating head when printing at gradations @3'', 14'', and @5'' shown in FIG. 4, and FIG. 6 is a circuit diagram of the gradation control circuit.

As shown in Figure 5, the upper and lower halves of each pixel (4 x 4 dots) are printed in time division, and the left and right halves of each pixel are printed simultaneously (in parallel) or Printed sequentially. One dot is printed twice, in the first half and second half, with a dot of intermediate density being formed in the first half cycle T1, and the same dot being reheated in the second half cycle T2, resulting in the maximum purity. dots are formed.

In Fig. 6, the information between the surfaces of one sheet is written in a pixel memory (not shown), and one page is written in accordance with the printing timing.
It is read out horizontally line by line or by several pixels. The data read out in the first access to the image memory for printing the upper half of the pixel is applied to a decoder (1), where it is developed according to the gradations it represents. For example, if the data is gradation ``5'', the signal will be output from the 5th layer of the decoder (1), and the signal will be output from OG3 to OG
7 through and gate person G1, AG3, person G5, λG
6. You can input to each of AG7. At this time, the up/down control signal is 1 above 'm1 and the number of times control signal is 'H' (first time), so the outputs of AND gates AG1 and AG5 are outputted by OR gate OG8.0G9flk and the buffer memory (
21 is further sent as a serial signal from the buffer memory (2) to the next stage drive system, and the first printing (1-7 tones) is performed as shown in the time chart of FIG.

When the first printing information is sent out, the image memory is accessed again and the same data is supplied to the decoder (1). At this time, the number control signal becomes lLI'' (second time), so only the AND gate AG6 is opened and the 5th vA
Only the upper right dot is printed again as shown in the time chart. As a result, printing is performed in which the right side is black and the left side is halftone, as in the upper half of the 15'' pattern in FIG.

When the upper half of the pixels for one line has been printed as described above, the up/down control signal is switched to 10,000, which is 1 down.
The same process as described above is performed again to print the lower half of the pixel.

According to the above-described embodiment, since dots with large density differences (black and white) are not mixed in one pixel, an image with smooth gradation can be obtained, and the apparent resolution is reduced.

Next, a printing device in which the present invention is applied to the dither method will be described. In the example of wJ2 in C, as shown in the density level diagram in Figure 7, a 61-step gradation image was obtained using a thermal printer that can stably obtain color density in 16 steps (0 to 15). I'm trying to be able to do that. That is, the areas 81 to B, 6 of each level are substantially divided into four levels,
Including white printing, 15×4+1=61 gradations are created.

For each region S, ~S1B, a 2×2 dither matrix (total 15 (II)) is prepared, and a dither method is applied to each region.A 2×2 dither matrix for the region Sn The threshold value of Dn is Dn=Do +
(n-1) U −・−−−−−−−−−(t)Do−
(00,5 0,250,75) (U: Each element of 2×2 or a unit matrix with all 1s) is given. For example, when n = 5, it becomes 44.5 D5"" (4,254,75). The level of the input data is determined based on this dither matrix, and dither values 0 and 1 are determined. As the print density, the density at both ends of the area where the input data level is entered is used. For example, in area S6, when the dither value is "0", the density level is @5" and the dither value is 1.
'', the density level ``6'' is reassigned.

Figure 8 is this #! FIG. 9 is a block diagram of the gradation control circuit according to the second embodiment. FIG. 9 M1 to M15 are schematic diagrams of dither matrices determined by formula 181, FIG. 10 is a route map of the print screen, and FIG. 11 is a diagram of each dither matrix. Indicate each element
It is a schematic diagram.

The 15 dither matrices shown in FIG. 89 are separated into an upper dot group and a lower dot group, and are stored in the matrix memory (4) in FIG. Each group of upper two dots is written to y addresses 1-15, and each group of two lower dots is written to addresses 17-31.

81.0 When the sample data (analog value) of the 1st line pixel/161 of the T print screen shown in Figure 8 is input to the terminal (5) in Figure 8, the switch number in Figure 8g8 is 1 left, switch aυ. is set to the 1-up'' position, and the address counter a4 starts counting the clock pulses CK from the terminal (9) T'.The switch QI (Ql) is switched and controlled by the output of the address controller a field. Based on the horizontal synchronization signal H1 and the vertical synchronization signal V% sample pulse given to terminals (6) to (8), the address controller
Create a switching control signal that corresponds to the address of all print screens.

The output of the counter a2 is converted into an analog value by the D/A converter (13) and sent to the comparator αhiro to be compared with the input data. When the output level of the D/A converter exceeds the input data, the address Counter a is stopped. Counter a)
The output of is given to the memory (4) as address data via switch q1), the upper data of the T dither matrix shown in FIG. 11 is read out, and the data on the left side is further selected by switch 4.

For example, when the input data level is 3.4 and the address counter a counts 4, this counter is stopped, so the dither matrix corresponding to area S4 in FIG. ) is selected, and the upper left threshold value a4=6 is read ffl? It will be done. The threshold value 14 of C is sent to one comparator of FIG. 8 and compared with the input data to determine the dither value @0"'"1".

This dither value is used to operate the switch aQ, and when the dither value is 10'', the data obtained by subtracting 1 from the output of the address counter a2 with a subtracter (1?) is used, and when the dither value is ``1'', the data is obtained by subtracting 1 from the output of the address counter a2. The output of a2 itself is switch Q
Selected with f9. The output of the switch af9 indicates the print density (one of 16 levels) of the pixel 41.

For example, if the input data level is 3.4 as described above, the address value 4 is read and compared with the threshold value 3, which is ff15, and the dither value @0'' is determined.
Printing is performed at density level 3, which is obtained by subtracting O.Next, when the sample data of /I62 on the first line in Figure 10 is input, the switch Q (i is set to 1 right), and the ) The threshold value of the IJ Lux upper cloth is read out. Then, the dither value is determined in the same manner as described above, and the print density level is determined based on this dither value.

Thereafter, when the sample data of /I63 is input, switch 4 is alternately switched to 1" to the left, and to 1 to the right for /I64, thereby processing one line of data.

When the processing of the first line is completed, the switch aυ is switched to the lower side, and the processing of the next second line is performed. sio
In the pixel *n+1 of line T2 shown in the figure, address data obtained by adding 16 to the output of the address counter a2 by the adder α barrel is supplied from the switch αυ to the memory (4), so that the matrix shown in FIG. The lower left threshold C of
is read out, and in the pixel An+2 next to it, the switch G
By switching o, the threshold value d on the lower right side of the matrix is read out.

Furthermore, in the next line, the switch θυ is switched to "1 above", and thereafter, the switch αυ is alternately switched to "9 above" for each line.
``Down'' and processing is performed on the entire screen.

For example, the input data level of four minute pixel groups t that are adjacent to each other vertically, horizontally, and vertically is 3.4 3.4 (3,,s s , 4) ``”””” (21
In this case, for each address value counted by counter α or T, it becomes (44...................................(3)44).Therefore, based on this address, matrix memory ( The threshold value of the dither matrix read out according to the selection of the switch aωαυ from 4) is as follows.This threshold value and the input data of the two equations are compared by the comparator Kasumi, and the next dither value is determined.

(81)・・・・・・・・・・・・・・・(5) Based on this dither value, the address value t of the three formulas is corrected by 0 or -1, so the print density of each dot is is (34 34n . . . . . . . (6). Therefore, with 16 gradations, the print density for the input data 3.4 of the second equation is 6. However, when the dither method is applied, as shown in equation 6, for a group of 4 pixels adjacent to each other (top, bottom, left, right, top), on average (5
+5+4+4)/4=5.5 intermediate gradations are obtained. That is, a printing screen with 61 different gradations can be obtained.

If you want to obtain 61-gradation expression using the conventional dithering method that uses black and white binary values or the dot density control method shown in Figure 1 or IIK2, 8x8 dots are required! However, in the @2 embodiment, only 2×2 dots are required, which is extremely advantageous in terms of resolution.

In addition, within each density region, based on the obtained dither value, the vicinity of the true density (il
K level) is selected, so that dots with large density differences do not coexist within one pixel group (K level), smooth gradation expression can be performed, and a more natural image can be obtained. By making it smoother, the apparent resolution is the same as above.Furthermore, since the dither method is applied,
Although it is advantageous in terms of resolution compared to the one system shown in Fig. 3 that uses both dot density control and print density control, it is still
In the example, if the dither matrix is 3×6, then 1
It is also possible to express 66 gradations.

Although serial processing is performed on each sample data, parallel processing is also possible.

As described above, the present invention makes the maximum gradation difference between each dot in one pixel or one group of pixels smaller than the gradation difference between the highest gradation level and the lowest gradation level, resulting in smoother gradation. An image with tone expression can be obtained, and the apparent resolution is also improved.

Figure 4 shows an embodiment of wLl of the present invention.
Printing concept diagram, It! 5WJ is the gradation level in Figure 4 @3”, 14
6 is a circuit diagram of the gradation control circuit, and FIG. 7 is the density level line 7 in the 1!2 embodiment of the present invention. figure,@
Figure 8 is a block diagram of the gradation control circuit according to this embodiment of It12, Figure 9 KM1-M15 is a schematic diagram of the dither matrix determined by the formula 1, Figure 10 is a route map of the print screen, and Figure 11 is FIG. 3 is a schematic diagram showing each element of each dither matrix.

In addition, in the symbols used in the drawings, (4)・・・・・・・・・・・・Matrix memory a is equipped with switch a.
・・・・・・・・・・・・Address counter α■・
・・・・・・・・・・・・D/A converter Qa5...
・・・・・・・・・Comparator αe・・・・・・・・・・・・
・・・・・・Switch αD・・・・・・・・・・・・・・・
・Subtractor αQ・・・・・・・・・・・・It is an adder.

Agent Katsu Ueya Figure 1 Figure 2 Figure 3 □　　　　　　Figure 4

Claims (1)

[Claims] In an image recording device in which one pixel or one group of pixels is composed of a plurality of dots and each dot is recorded at a predetermined level of gradation, the difference between each dot in one pixel or one group of pixels is An image recording device characterized in that the maximum gradation difference is smaller than the gradation difference between the highest gradation level and the lowest gradation level.