Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-09-24
2003-11-25
Nguyen, Thinh (Department: 2061)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000
Reexamination Certificate
active
06652059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and image processing method and, more particularly, to image processing of converting data of each pixel into data of a smaller number of gray levels than the number of input gray levels in a printing apparatus which performs printing by moving a printhead having a plurality of printing elements arrayed in a predetermined direction, relatively to a printing medium.
BACKGROUND OF THE INVENTION
As an information output apparatus for a wordprocessor, personal computer, facsimile apparatus, or the like, a printing apparatus which prints information such as a desired character or image on a sheet-like printing medium such as a paper sheet or film may use various methods. Of these methods, a method of applying a printing agent to a printing medium to form text or an image on the printing medium is put into practical use. A typical example of this type is an ink-jet printing apparatus. Recently, ink-jet printing apparatuses are attaining higher performance, and can print not only text but also images.
For higher printing speeds and higher image quality, the ink-jet printing apparatus uses a nozzle group constructed by packing and arraying a plurality of ink orifices (nozzles) capable of discharging ink of the same color at the same density. Such nozzle groups are generally arranged for ink of the same color at different densities or inks of different colors. Some apparatuses can discharge ink by changing stepwise the discharge amount of ink of the same color at the same density.
The printhead having these nozzle groups is moved relative to a printing medium, and discharges ink from the nozzles to print.
To print an image, a halftone processing method such as dithering or error diffusion is employed as a method of exactly reproducing the tone of image information. For example, an error diffusion method by R. Floyd (“An adaptive algorithm for spatial gray scale”, SID International Symposium Digest of Technical Papers, vol. 4.3, 1975, pp. 36-37) is known as a method of converting multilevel image data into a binary image (or an image having the number of binary or higher gray levels which is smaller than the number of input gray levels). According to this error diffusion method, a binary error in a given pixel is diffused to subsequent pixels to realize a pseudo tone expression.
Error diffusion is widely adopted as a pseudo halftone processing method with high tone reproducibility in image processing apparatuses such as a printer, copying machine, and facsimile apparatus.
However, printing using error diffusion suffers from the following problem.
This problem will be described by exemplifying printing of an image by a serial printer such as an ink-jet printer in which a printhead having a plurality of nozzles arrayed in a predetermined direction scans a printing medium in a direction crossing to the nozzle array direction, and ink is discharged onto the printing medium to form an image.
A plurality of nozzles which discharge ink droplets (dots) include an (undischargeable) nozzle which cannot discharge dots under some influence, or a nozzle whose discharge dot volume does not reach a specified value. When using a large number of nozzles for a long nozzle array, there is a high probability of such abnormal nozzles being present.
FIG. 6
is a view showing a process of forming an image by one scanning operation of one image array (raster) using one nozzle array. Reference numeral
60
denotes a nozzle in a good discharge state;
61
, an unprintable nozzle which cannot discharge dots;
62
, a binarization result by an error diffusion method; and
63
, a dot printing state.
When an image is formed by one scanning operation, no dot can be printed on a printing medium in a raster corresponding to an unprintable nozzle, as shown in FIG.
6
. If dots must be formed in the raster corresponding to the unprintable nozzle by binarization processing complying with a conventional error diffusion method, an image around the dots is formed from dots smaller in number than dots which should be actually printed. In other words, density conservation as one of advantages of error diffusion cannot be fully achieved, greatly degrading the printing image quality.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image processing apparatus capable of printing a high-quality image even when printing using a printhead having a printing element which cannot print normally.
It is another object of the present invention to provide an image processing method capable of printing a high-quality image even when printing using a printhead having a printing element which cannot print normally.
According to the first aspect of the present invention, the above object is attained by an image processing apparatus for a printing apparatus which performs printing by moving a printhead having a plurality of printing elements arrayed in a predetermined direction, relatively to a printing medium, comprising: determining means for determining whether input pixel data is pixel data to be printed by a printing element which cannot print normally; quantizing means for converting input multilevel data of each pixel into data of a smaller number of gray levels than the number of input gray levels; and error diffusing means for diffusing a difference between input data and data quantized by said quantizing means for a pixel of interest to pixels around the pixel of interest, wherein the quantizing means performs, for the pixel data determined by the determining means to be printed by the printing element which cannot print normally, quantization processing different from quantization processing for other pixel data.
According to the first aspect of the present invention, another object is attained by an image processing method for a printing apparatus which performs printing by moving a printhead having a plurality of printing elements arrayed in a predetermined direction, relatively to a printing medium, comprising: the determining step of determining whether input pixel data is pixel data to be printed by a printing element which cannot print normally; the quantizing step of converting input multilevel data of each pixel into data of a smaller number of gray levels than the number of input gray levels; and the error diffusing step of diffusing a difference between input data and data quantized in the quantizing step for a pixel of interest to pixels around the pixel of interest, wherein in the quantizing step, the pixel data determined in the determining step to be printed by the printing element which cannot print normally undergoes quantization processing different from quantization processing for other pixel data.
The above objects are also attained by a computer program which causes a computer to execute the image processing method, and a storage medium which stores the program.
More specifically, according to the first aspect of the present invention, in a printing apparatus which performs printing by moving a printhead having a plurality of printing elements arrayed in a predetermined direction, relatively to a printing medium, whether input pixel data is pixel data to be printed by a printing element which cannot print normally is determined. Input multilevel data of each pixel is converted into data of a smaller number of gray levels than the number of input gray levels. The difference between input data and quantized data of a pixel of interest is diffused to pixels around the pixel of interest. In quantization, the pixel data determined to be printed by the printing element which cannot print normally undergoes quantization processing different from that for other pixel data.
The pixel data determined to be printed by the printing element which cannot print normally undergoes processing different from that for other pixel data, e.g., processing of adding the data to an error applied to neighboring pixels. As a result, the pixel data can be diffused to neighboring pixels.
Even in printing using a printhead with
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Thinh
LandOfFree
Image processing apparatus and image processing method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image processing apparatus and image processing method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image processing apparatus and image processing method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3127415