Facsimile and static presentation processing – Static presentation processing – Attribute control
Utility Patent
1997-12-29
2001-01-02
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S534000, C358S451000, C358S451000
Utility Patent
active
06169608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of converting a color continuous tone image into a pseudo-halftone color image.
2. Description of Related Art
There has been proposed a color printer capable of printing color images with color ink.
SUMMARY OF THE INVENTION
When desiring to obtain a high quality print output, it is conceivable to increase resolution, at which the image is to be printed. For example, when desiring to print a high quality color image, a color printer is controlled at a resolution of 720 dpi, which is higher than a normal resolution of 360 dpi that is used at a normal printing operation.
At a certain region represented by image data to print all dots therein, the number of dots printed in that region at, the high, 720 dpi resolution will become four times as large as the number of dots printed in that region at the normal, 360 dpi resolution. During the high resolution printing, therefore, the amount of ink placed on the sheet of paper will become four times as large as that of the ink to be placed on the sheet of paper at the normal resolution printing. Accordingly, a cockling phenomenon will possibly occur. That is, the sheet of paper will become wrinkled. Ink will drop along the sheet of paper.
In order to solve this problem, the printer can be provided with a control mechanism for limiting the total amount of ink to be ejected onto the sheet of paper. That is, an upper limit is determined onto a multilevel density of the input image which is to be converted into a bilevel density. Then, the thus level-limited multilevel density is converted into a binary value through an error diffusion binary conversion method, a dithering binary conversion method, or the like. Because the multilevel data is limited by the upper limit, it is possible to prevent all the dots from being printed.
It is assumed that the upper limit is set as 75% of the highest density value inputtable to the printer as multilevel data. It is also assumed that a color continuous tone image to be printed is comprised of three color component data: cyan data C, magenta data M, and yellow data Y.
When a certain image portion in the continuous tone image has density values of 100% for all the components, this image portion should be printed as black. If the above-described ink amount limiting control is achieved onto this image portion, density data for each color component will be decreased to 75% of the original value. That is, C=75%, M=75%, and Y=75%. The thus adjusted color component densities are then subjected to the binary conversion process such as the error diffusion binary conversion, the dither binary conversion, or the like. As a result, dots will be distributed only at 75% of all the dot positions in the subject image portion.
This image portion, however, should appear black. That is, dots of all the color components should be located one on another at each dot location, thereby presenting black color according to a subtractive color mixing method. When the dots are distributed only at 75% of all the dot locations, however, dots of all the color components will not be located one on another. There will be distributed: single color dots of cyan, magenta, and yellow; two color-mixed dots produced by two of the three color components; and three color-mixed dots properly produced by the three color components. The subject image portion will appear as different from black because those different types of dots will be visually perceived according to an additive color mixing method. Accordingly, the reproducibility of the image portion will be greatly deteriorated.
The binary conversion method can be modified as described below. That is, when data of all the three color components C, M, and Y for one pixel position is turned ON, the corresponding pixel is replaced with a single black dot K. For a black-representing pixel, therefore, only a single black dot will be located. It is unnecessary to provide the three color dots. It is possible to effectively prevent occurrence of the cockling phenomenon or the occurrence of ink dropping phenomenon.
Color components C, M, and Y may be subjected to the ink amount limiting control before they are subjected to the thus modified binary conversion process. In this case, however, color components C, M, and Y indicative of a black color region may possibly fail to be turned ON. Also in this case, the black-representing region will be reproduced by mixture of: single color dots of cyan, magenta, and yellow; and two color-mixed dots produced by two color component dots; and black dots. This image region will fail to represent accurate black color.
It is additionally noted that each of the single color dots of cyan, magenta, and yellow and the two color-mixed dots should have been converted into a single black dot K. Accordingly, the number of dots located in that black image region increases in comparison with the case where those dots are properly converted into black dots only. In other words, the ink amount limiting control makes it difficult to prevent occurrence of cockling phenomenon.
In order to solve this problem, it is conceivable to decrease the amount of the upper limit set in the ink amount limiting control. In this case, the coloring state of a resultant image will be further shifted from a desired state. The printing quality will be greatly deteriorated.
An object of the present invention is therefore to solve the above-described problems and to provide an improved color image binary conversion method which is capable of converting a continuous tone color image into a pseudo-halftone color image at a high resolution while not deteriorating the printing quality and while limiting the amount of ink to be ejected, thereby preventing occurrence of the undesirable cockling phenomenon.
In order to attain the above and other objects, the present invention provides a method for converting continuous tone color image data into pseudo-halftone color image data, the method comprising the steps of: successively judging whether or not each of a plurality of pixels, arranged in a continuous tone color image, is located at a predetermined printing-prohibited pixel position, while comparing, for each of a plurality of different color components, density data of at least one pixel other than that located at the printing-prohibited pixel position, with a threshold value; and compulsively converting the density value into the binary value of OFF when the subject pixel is judged to be located at the predetermined printing-prohibited pixel position and converting the density value into a binary value of either ON or OFF based on the compared result when the subject pixel is judged not to be located at the predetermined printing-prohibited pixel position.
According to another aspect, the present invention provides a program storage medium for storing data of a program indicative of a process for converting continuous tone color image data into pseudo-halftone color image data, the program comprising: a program of successively judging whether or not each of a plurality of pixels, arranged in a continuous tone color image, is located at a predetermined printing-prohibited pixel position, while comparing, for each of a plurality of different color components, density data of at least one pixel other than that located at the printing-prohibited pixel position, with a threshold value; and a program of compulsively converting the density value into the binary value of OFF when the subject pixel is judged to be located at the predetermined printing-prohibited pixel position and converting the density value into a binary value of either ON or OFF based on the compared result when the subject pixel is judged not to be located at the predetermined printing-prohibited pixel position.
According to still another aspect, the present invention provides a printer for converting continuous tone color image data into pseudo-halftone color image data and for printing the pseudo-halftone color image, the
Brother Kogyo Kabushiki Kaisha
Lee Thomas D.
Oliff & Berridg,e PLC
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