JP2716090B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for inputting multi-valued image data and binarizing the same, and in particular, for determining the density of pixels input from a scanner, a television camera or the like. The present invention relates to an image processing apparatus for binarizing digital multi-valued image data into binary signals of on / off and outputting the binary signals to an inkjet printer. 2. Description of the Related Art Conventionally, in an image processing apparatus of this type, image data having so-called depth information such as a color image or a gradation image sent from a host computer or the like is output from a line printer such as an inkjet printer. When printing is performed by a device, binarization is generally performed by retrieving comparison data of a fixed threshold pattern matrix from a memory (storage device) and comparing it with input image data. That is, as is well known, image data having such depth information is data representing the gradation of pixels and the like in a digital amount. In a binary output type line printer or the like, such data is printed as it is. Since it cannot be performed, it must be binarized before inputting to a line printer or the like. Therefore, as a conventional method for expressing the gradation by a line printer or the like, a group of a plurality of dots is defined as one pixel, and one group is defined according to the gradation level of the input image data.
There is an image processing method that expresses the gradation (shading of an image) by determining which dot is to be printed or not to be printed in a pixel. However, when an image is printed in this way, other pixels are printed. Is not balanced, false contours are generated and the print quality is degraded. Therefore, by defining an output pattern different from these input pixels and comparing the pattern with image data having depth information, a method of appropriately expressing the gradation in a large range, that is, by a threshold pattern comparison A binarized image processing method (including a dither method) is generally adopted. FIGS. 13A and 13B are schematic configuration examples of a conventional binarized image processing method in which such multivalued image data is printed using binarized data obtained by comparison with a threshold data matrix (data). Is shown. In this conventional method, multivalued image data 1
For example, a 4 × 4 pattern as shown in this figure is prepared as a threshold matrix 2, and both 1 and 2 are compared by a comparator 3 to be binarized. The data is read out from the line memory 4 at the timing shown in FIG. 14 and output by the line printer in dot printing as indicated by reference numeral 5. In this case, since the threshold matrix 2 is a 4 × 4 pattern, 17 (= 16 + 1) gradations can be expressed by the area gradation method. By increasing the size of the threshold value matrix 2, further fine gradation can be obtained. For example, if the size is 8 × 8, 65 (= 64 + 1) gradations can be expressed, and if 12 × 12, 145 (= 144 + 1) gradations can be expressed. [Problems to be Solved by the Invention] In other words, in such a conventional image processing method,
Only 17 gradations can be obtained in a × 4 matrix area, and in order to further increase the gradation, a high-level halftone cannot be expressed unless the matrix area is increased, such as an 8 × 8 matrix area. However, when the size of the threshold matrix is increased in this way, there is a disadvantage that the resolution of the output print is greatly reduced and the granularity is conspicuous, instead of increasing the gradation. Therefore, if the image data is 8-bit multi-valued image data, 25
In the case of having a density level of 6 gradations and performing binarization and area modulation by the conventional method as described above and performing print output, the resolution and granularity are not significantly reduced.
For example, as described above, the gradation level has to be compressed to 17 levels by using a 4 × 4 threshold matrix, so that the gradation must be considerably sacrificed to express the halftone. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing apparatus which can eliminate the above-mentioned drawbacks, increase the gradation in an inkjet recording system, and improve the resolution. [Means for Solving the Problems] To achieve the above object, an image processing apparatus according to the present invention comprises:
The binary image data is supplied to an ink jet recording apparatus that forms recording dots by repeatedly hitting flying droplets ejected from nozzles at substantially the same location on a recording material N times in response to input of binary image data. In the image processing device,
Input means for inputting multi-valued image data; and multi-valued image data input by the input means are applied to each of the N times of overprinting so as to increase the number of gradations that can be expressed by the N times of overprinting. Based on parameters set to mutually different values so that different binary image data can be generated when the multi-valued image data of the same pixel is expanded into binary image data in correspondence with the binary image data, the binary image data is sequentially converted N times. Developing means for developing, wherein the input means inputs the multi-valued image data of the same pixel N times, and the developing means performs multi-valued image processing by the input means at the time of overprinting by the ink jet recording apparatus. It is characterized in that the development into the binary image data is sequentially repeated N times based on the mutually different parameters in response to the data input. [Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. A. Principle of Dot Diameter Growth As described above, in the present invention, the gradation is increased without changing the size of the threshold matrix by changing the dot diameter by overprinting in the ink jet recording method. Therefore, first, the growth of the dot diameter by overprinting will be described. As shown in FIGS. 3A to 3D, when the ejection signal S of the ink jet printer is continuously applied to a heating element (not shown) in the nozzle 6, a number corresponding to the number of pulses of the ejection signal is obtained. Ink droplets 7 are ejected from the nozzles 6 and bleed while the inks are fused on the paper at the same position.
Dot diameter grows. In addition, as the dot diameter increases, the density of the print dot itself denoted by reference numeral 8 also increases due to the overprinting, thereby changing the gradation. FIGS. 4 (A) to 4 (C) show a case where the output interval (t ₂ , t ₃ ) of the first dot and the second dot is widened, but the dot density increases as the output interval (time) increases. The dot diameter growth becomes dull because the ink droplet of the next dot is ejected after the ink droplet of the previous dot has sufficiently penetrated, and the dot diameter becomes smaller. FIG. 5 shows the relationship between the number of output dots, the size of the dot diameter, and the time interval between output dots in this overprinting. In the embodiment of the present invention, which will be described later, the characteristics of the dot diameter growth and the number of dot overlaps described above are used to express smooth gradation by changing the data of the threshold matrix in accordance with the order of overprinting. Is made possible. In FIG. 3 described above, four dots are overprinted as an example. However, if the performance of the nozzle 6 is improved to achieve ejection of ink droplets of dots, and if up to eight dots can be overprinted, four dots are overprinted. 65 (= 4 × 4 ×
With 4 + 1) gradation, fine gradation expression can be performed up to 129 (= 4 × 4 × 8 + 1) gradation without changing the size (output area) of the threshold matrix. Also, if the pattern size of the threshold matrix is further expanded to 8 × 8, even if 4 dots are overprinted,
Up to 257 (= 8 × 8 × 4 + 1) gradations can be expressed, and the previous area of the input image data can be covered. B. Circuit Configuration of Embodiment FIG. 1A shows a schematic configuration example of an image processing apparatus of an ink jet printer to which the present invention is applied, and FIGS. 1B and 1C show operation examples thereof. In FIG. 1A, reference numeral 10 denotes a pattern memory in which a plurality of threshold matrices as shown in FIGS. 1B and 1C are stored in advance. The pattern memory 10 is provided with a plurality of different threshold matrices as shown in FIGS. 1B and 1C in accordance with the order of overprinting. The pattern memory 10 shown in FIG. 1B is not one in which four 4 × 4 dither matrices are arranged side by side. In this example, the pattern memory 10 corresponds to four overstrikes for each nozzle 6 for discharging dots. The four thresholds are arranged as a unit. That is, the first
When the four dither matrices shown in FIG. 3C are aligned in the nozzle units from the first column to the fourth column, the threshold data of the pattern memory 10 in FIG. 1B is obtained. Although the image data 1 input to the comparator 3 is 8-bit digital multi-valued data, the comparator 3 binarizes 0 and 1 for printing by an ink jet printer. But,
Since gradation cannot be expressed for each dot simply by binarization as in the prior art, binarization is performed for each overstrike by comparing with a plurality of threshold matrices as described later. This is referred to as dot development. When the image data 1 is input to the comparator 3, the comparison data (threshold) is read from the pattern memory 10 in which the above-described threshold is written.
Are sequentially output to the comparator 3, and the image data 1 is
Is binarized to print data (ejection signal) S of 0,1. Here, when the image data 1 is made to correspond to a 4 × 4 dot matrix, the threshold data is called 16 times for one input image data 1 for one overstrike and is binarized. You. For example, assuming that the level “32” of the image data 1 is input, first, the threshold value matrix of 4 × 4 is compared with the comparator 3 and binarized. The binarized data is written to the line memory 4, and the data is read out as the ejection signal S from the line memory 4, applied to the heating element of the nozzle 6, and printed. The data from the line memory 4 is sent to each heating element of the nozzle 6 at the timing shown in FIG. 2, and when the ink droplets are overprinted a predetermined number of times, the carriage of the print head or the recording paper (not shown) moves. C. Configuration Example of Pattern Memory Next, the contents of the pattern memory 10 will be described in more detail with reference to FIGS. 1 (B) and 1 (C). The pattern memory 10 includes the threshold pattern matrix including the overlapping direction,
A 4 × 4 × 4 matrix is prepared, and the matrix and the multivalued image data 1 are compared by the comparator 3. The threshold pattern matrix has four times the memory size of the conventional 4.times.4 threshold value in the case of 4-dot superimposition in order to prepare data in the overstrike direction. And image data 1
Is also quadrupled. The output data binarized to 0 and 1 in the comparator 3 according to the overprint pattern design is input to the line memory 4 as described above, and is converted into the ejection signal S of the ink jet. In FIG. 1 (B), “1100” is placed at the top of the first column.
Is held, indicating that two dots are overprinted in this case. D. Output Timing The output of the data transfer S1 and the output of the ejection pulse S2 in this embodiment are performed four times before the movement pulse S3 is input, for example, in the case of four-dot overlapping as shown in FIG. The number of times that the data transfer S1 and the ejection pulse S2 that are input between the movement pulse S3 to the carriage or the paper feed motor and the ejection pulse S2 are input determines the number of times of overstrike. The longer the interval of the movement pulse S3, the more
The number of dots to be shot is large, and the shorter the pulse interval, the more dots are shot at shifted locations on the paper.
The cycle of the moving pulse S3 also plays an important role in dot diameter growth. In addition, the ejection dots tend to be more circular as they are hit in the same location, and tend to be elliptical as they are ejected in shifted locations. Furthermore, the interval of generation of the ejection pulse S2 is
Assuming that t ₁ and the generation interval of the movement pulse S 3 are t ₂ , the relationship of t ₁ × the number of superpositions <t ₂ is that the dots are driven into the same place and become circular dots, and the gradation of dot diameter growth tends to be easily performed. It is in. In the above description, the output data of the line memory 4 is "1100"
Although the case of dot overprinting has been described, if the output data is "1111", it is four dot overprinting, and if it is "1110", it is three dot overprinting. Further, as in the case of output data "1001", it is possible to realize the overprinting with a time interval between the first dot and the second dot. In this case, as shown in FIGS. 4 (C) and 5 described above,
The growth of the dot diameter becomes gradual, and only the density by overprinting is improved. E. Types of Threshold Matrix FIGS. 6 to 8 show examples of the types of threshold matrix stored in the pattern memory 10 described above. 6 (A), FIG. 7 (A), and FIG. 8 (A), the threshold matrices are arranged for each nozzle from the first row to the fourth row, as in FIG. 1 (B). Things. First, the threshold matrix 10A shown in FIG.
Is a distributed threshold matrix similar to that shown in FIG.
As shown in FIGS. 8B to 8D, the first dot is shot over the entire area, and the second dot, the third dot, and the fourth dot are overprinted on average. The threshold matrix 10B shown in FIG. 7 (A) is a centralized threshold matrix, which is intensively driven into the same place as shown in FIGS. 7 (B) to (D) and gradually spreads. The threshold matrix 10C shown in FIG. 8 (A) is an irregular concentrated threshold matrix similar to that shown in FIG. 1 (C), and as shown in FIGS. After striking, the location is changed and an overstrike pattern that spreads is obtained. By changing the order of overprinting in this way, the gradation can be controlled, and by changing the content of the threshold pattern,
A fine gradation can be obtained in consideration of [dither + dot diameter growth + density change of overprinting]. F. Embodiment Using Look-Up Table System FIG. 9 shows the configuration of another embodiment of the present invention. In this embodiment, a ROM (read only memory) is used for input image data 1 together with addresses indicated by X and Y. ) Is called out from the look-up table 20 stored in the line table 4 and sent to the line memory 4 for printing by the ink jet printer. This lookup table 20 is, for example,
It has the output contents as shown in FIGS. 10 to 12, and performs the same operation as the threshold value matrix shown in FIGS. 6 to 8 described above. That is, by retrieving the input image data 1 and the data at the addresses indicated by X and Y from the look-up table 20, the overprint data similar to that shown in FIGS. 6 to 8 is sent to the line memory 4. . Here, FIGS. 10 (A) to (C) show the case of a distributed lookup table, FIGS. 11 (A) to (C) show the case of a centralized lookup table, and FIG. 12 (A). ) ~
(C) shows the case of an irregular centralized lookup table. FIGS. 10, 11, and 12 show the binarization results aligned for each nozzle, as in the case of the line memory 4 in FIG. 1 (B). The corresponding application results are the overprinted dither images 5 in FIGS. 6 to 8, respectively. Thus, also in the present embodiment, the design of the output pulse can be easily changed by rewriting the contents of the lookup table 20, and the same effect as in the first embodiment can be obtained. As described above, according to the embodiment of the present invention, the following effects can be obtained. Since a threshold value corresponding to the overstrike is prepared and the overstrike is performed by the ink jet printer, for example, 4
Conventionally, a 4 × 4 pixel matrix is 17 (= 16 +
1) Although only gradation can be expressed, 65 (= 64 + 1) gradations can be expressed by overlapping four dots, and the gradation can be significantly increased. Further, by changing the overlap interval, it is possible to increase only the density by overlapping dots without increasing the dot diameter, and to obtain a smooth gradation characteristic as a whole. In addition, by reducing the dot diameter, it is possible to increase the dot diameter, thereby obtaining finer gradation. For example, by realizing 12-dot superimposition, a high gradation such as 192 (= 4 × 4 × 12) gradation can be obtained, and the gradation can be increased without reducing the resolution. Can be. Since it is easy to improve the overprinting head of the present invention using the existing inkjet head as it is,
It can be realized relatively inexpensively and easily. [Effects of the Invention] As described above, according to the present invention, when overprinting is performed by an inkjet recording apparatus and a gradation image is reproduced, for example, the number of times that overprinting can be performed differs depending on the connected inkjet recording apparatus. Is also highly versatile that can be handled simply by adjusting the number of deployments by the deployment means,
Moreover, it is possible to provide an image processing apparatus in which the circuit configuration for overstrike is simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (A) is a block diagram showing the configuration of an embodiment of the present invention, and FIGS. 1 (B) and 1 (C) show the operation of the embodiment of FIG. 1 (A). FIG. 2 is a timing chart showing the output timing of the embodiment of FIG. 1 (A), FIG. 3 is an explanatory diagram showing the relationship between the number of overprinted dots and the growth of the dot diameter in the embodiment of the present invention, FIG. FIG. 5 is an explanatory view showing the relationship between the time interval of overstrike and the dot diameter growth in the embodiment of the present invention. FIG. 5 is a characteristic diagram showing the dot diameter growth characteristics of the embodiment of the present invention. 8 is an explanatory diagram showing an example of a threshold matrix of the embodiment of the present invention and an output form thereof, FIG. 9 is a block diagram showing a configuration of another embodiment of the present invention, FIG. 10, FIG. 11 and FIG. FIG. 13 is an explanatory diagram showing the operation of the lookup table according to the embodiment of the present invention. Diagram showing a schematic configuration example of a coming apparatus, FIG. 13 (B) is an explanatory view showing an operation of the conventional device, FIG. 14 is a timing chart showing the output timings of the conventional apparatus. 1 ... input image data (digital multi-valued image data), 2 ... threshold matrix, 3 ... comparator, 4 ... line memory, 5 ... print output, 6 ... nozzle, 10 ... pattern memory, 20 ...... Lookup table.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kentaro Matsumoto               3-30-2 Shimomaruko, Ota-ku, Tokyo               Inside Canon Inc. (72) Inventor Toyokazu Uda               3-30-2 Shimomaruko, Ota-ku, Tokyo               Inside Canon Inc. (72) Inventor Akemi Fukumoto               3-30-2 Shimomaruko, Ota-ku, Tokyo               Inside Canon Inc.                (56) References JP-A-62-88476 (JP, A)                 JP-A-50-57321 (JP, A)                 JP-A-59-189782 (JP, A)

Claims (1)

(57) [Claims] 1.2 Ink jet forming a recording dot by N times jetting a flying droplet ejected from a nozzle on substantially the same location on a recording material in response to input of binary image data In an image processing apparatus for supplying the binary image data to a recording device, an input unit for inputting multi-valued image data, and the multi-valued image data input by the input unit can be expressed by the N times of overprinting. Different values are set so that different binary image data can be generated when multi-valued image data of the same pixel is developed into binary image data corresponding to each of the N times of overprinting in order to increase the number of gradations. Developing means for sequentially developing into binary image data N times based on the parameters set in the input device, wherein the input means inputs the multi-valued image data of the same pixel N times and The means sequentially repeats the development into binary image data N times based on the mutually different parameters in response to the input of multi-valued image data by the input means at the time of overprinting by the ink jet recording apparatus. Image processing device.