Halftone Dot Formation Method and Apparatus for Reducing Layer Thickness of Coloring Material Inside Halftone Dots, and Image Formation Apparatus

Abstract

An image processing method generates a halftone-dot image by forming a halftone dot, which is represented by a set of one or plural output dots and corresponds to an intensity of an input image signal, while making a part of the dots constituting the halftone dot to be an actual non-output dot so as to reduce an amount of a coloring material of the halftone-dot portion. When the intensity of the image signal exceeds a predetermined value and is in a predetermined range, while maintaining contour dots, which are output dots contribute to formation of a contour of the halftone dot, to be the output dot, the image processing method makes a part of dots inside the contour dots to be the actual non-output dot.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This is a Division of application Ser. No. 11 / 357,950 filed Feb. 22, 2006. The disclosures of the parent application and Japanese Patent Application No. 2005-45107 filed on Feb. 22, 2005 and Japanese Patent Application No. 2006-32016 filed on Feb. 9, 2006, including the specifications, claims, drawings and abstracts are incorporated herein by reference in their entirety.BACKGROUND[0002]1. Field of the Invention[0003]The present invention relates to an image processing method, an image processing apparatus, and an image forming apparatus. More specifically, the invention relates to a binarization processing technique for generating a halftone-dot image by forming a halftone dot having a predetermined size corresponding to an intensity of an input image signal, the halftone dot which is used to record a halftone-dot image on an image recording medium in a printing technique such as an electrophotographic method and an inkjet method.[0004]2....

AI Technical Summary

Benefits of technology

[0020]The invention provides mechanism, which can thins a coloring-material layer in a halftone-dot portion while suppressing errors in densities of the output image and preventing image quality from deteriorating when density of a halftone-dot image is reproduced in a pseudo manner by using halftone dots, regardless of a printing method such as an electrophotographic method using powder as a coloring material or an inkjet method using ink as a coloring material.

[0024]For example, as a shape of an original halftone dot, which is a process target, there are a so-called dot-shaped halftone dot (so-called dot screen), that is, an output dot growing into a substantially circle shape in response to density, and a line-shaped halftone dot having a structure in which a halftone dot is continued in a line shape in a range where the input image signal has a density equal to or larger than a predetermined density (so-called line screen). The dot screen is easy in forming a halftone dot, but is easily affected by disturbance at the time of image formation and color moire. To the contrary, the line screen has an advantage that it is less affected by the disturbance at the time of the image formation and the color moire.

[0025]If the invention of this application is applied to the dot-shaped halftone dot, the dot-shaped halftone dot becomes a ring-shaped halftone dot. Also, in the case of applying the invention of this application to the line-shaped halftone dot, for example, non-output dots are made to be continued in a line shape in the line-shaped halftone dot in a predetermined density range. That is, two methods can be adopted representatively; one is the case where gap is grown in the line-shaped structure to form a double line structure and the other is the case where non-output dots are maintained to be isolated in the line-shaped halftone dot, that is, the non-output dots are not continued in a line shape in the line-shaped halftone dot. The latter is better in reproducibility of the line structure.

[0026]Also, a pure-electronic mechanism may be configured so that the part of dots inside the contour dots is made to be a real non-output dot on electronic data representing the halftone dot, that is that an image recording signal inside the halftone dot is thinned out. Alternatively, a mechanism may be configured to modulate recording energy of the non-output dot inside the contour dots of the halftone dot on a basis of the binarized data generated by the binarization processing section so as to reduce an amount of coloring material.

[0028]According to the above configuration, only when the intensity of the image signal exceeds the predetermined value and is in the predetermined range, while the contour dots, which are the output dots contribute to the formation of the contour of the halftone dot, are maintained to be the output dot, the part of dots inside the contour dots is made to be the actual non-output dot. Therefore, a layer thickness of the coloring material inside the halftone dot can be reduced without the contour shape of the halftone dot made of the toner or ink being deformed.

[0029]Thereby, without deterioration of the image quality, the coloring material of the halftone-dot portion can be thinned effectively. Also, since a ratio of an amount of the coloring material contributing to light absorption is increased, the consumption amount of the coloring material can be reduced. Also, since the generation of the halftone dot and the generation of the gap are synthesized, control required for generating the gap dots inside the halftone dot is easy.

Problems solved by technology

Since the height of the piled-up toner is in many cases determined by an amount of toner required for the maximum density of the image, it may be an excessive amount of toner for halftone reproduction.

In particular, since the size of a halftone dot is small in a highlight tone area (low density region), there are high possibilities that this problem occurs.

However, it is difficult that the amount of toner needed for the maximum density is compatible with the amount of toner appropriate for the halftone dot reproduction.

However, as described above, in the halftone-dot structure for the halftone reproduction, the toner layer may become excessively thick in many cases, and therefore, the toner which makes a low contribution to light absorption exists on the paper.

However, in the FM screen such as the mechanisms disclosed in the patent document 1, since the density of the image is reproduced with a minute density of dots, which are invisible (30 μm or less), some of the integrated (clustered) minute halftone dots may be thinned out and areas of colored pixels may be too small to reproduce dots stably.

Accordingly, there may occur a phenomenon that the crush of some of the halftone dots is different from the crush of other halftone dots, which may result in image noises.

However, when many pixels are thinned out outside the halftone dots, since the size reduction of the halftone dots is significant but an operation of thinning out the coloring material in the halftone dot portion is weakened, an effect of making the halftone dots uniformly thin can not be expected.

In particular, since the size of the halftone dots becomes small in highlight tone area (low density area), there are high possibilities that the above-mentioned problems occur.

The dot screen is easy in forming a halftone dot, but is easily affected by disturbance at the time of image formation and color moire.

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