Image formation apparatus and image formation method
AssigneeSharp Kabushiki Kaisha
InventorsYoshinori Mutou, Tetsuro Toyoshima, Tadashi Iwamatsu, Nobuyuki Azuma, Yoshinori Nakajima
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Abstract
When a halftone image region that is below a predetermined density is to be reproduced, a processing unit controlling an exposure unit selects an exposure pattern that can represent a record dot diameter within a range based on a predetermined rule from exposure patterns prepared in advance. Accordingly, graininess is suppressed. When there are a plurality of exposure patterns that can be applied, the exposure pattern with the lowest number of dots present per 1 inch is employed. Accordingly, a halftone image is formed with the image reproducibility improved.
Claims10
An image formation apparatus comprising:
- an exposure unit conducting laser exposure on a photoconductor charged to a predetermined potential at a predetermined polarity to form an electrostatic latent image;
- a development unit applying a developer electrostatically to said electrostatic latent image for visualization;
- a storage unit prestoring a plurality of exposure patterns having dots scattered and arranged with a distance between adjacent dots set constant in both a main scanning direction and a sub scanning direction, a first table in which are stored density ranges that can be reproduced by respective exposure patterns and a second table in which are stored a correlation between a dot diameter and an output density of each exposure pattern;
- and
- a processing unit controlling said exposure unit in reproducing a halftone image region below a predetermined density, wherein said processing unit, in an operation of reproducing said halftone image region below a predetermined density,
- i) selects an exposure pattern corresponding to an input density value by referring to said first table,
- ii) when a plurality of exposure patterns are selected corresponding to said input density value, derives a dot diameter required for each of said plurality of exposure patterns by referring to said second table, and selecting an exposure pattern satisfying a relation of D/N≦0.4 where D is said dot diameter and N is the number of dots present per 1 inch in each of said plurality of exposure patterns, and
- iii) uses said selected exposure pattern to control said exposure unit.
An image formation method of effecting gray scale rendition, comprising the steps of:
- obtaining a density value of a pixel of interest,
- comparing said density value with a predefined density value,
- selecting an exposure pattern with respect to an input density value by referring to a first table storing a density range that can be reproduced by each of a plurality of preset exposure patterns in reproducing a halftone image region that is below a predetermined density,
- when a plurality of exposure patterns are selected for said input density value, deriving a dot diameter required for each of said plurality of exposure patterns by referring to a second table indicating a correlation between a dot diameter and an output density of respective exposure patterns, and
- selecting an exposure pattern satisfying D/N≦0.4 where D is said derived dot diameter and N is the number of dots present per 1 inch in each of said plurality of exposure patterns.
Dependencies are inferred from the claim text.