Image forming apparatus

Details Image forming apparatus Image forming apparatus

2000-09-15

2004-08-17

Williams, Kimberly (Department: 2626)

Facsimile and static presentation processing

Static presentation processing

Attribute control

C358S001900, C358S003130, C358S003260, C358S536000, C347S131000

Reexamination Certificate

active

06778298

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus for recording high-quality graduated images. More particularly, the invention relates to a technique of dividing an input picture into a plurality of blocks and converting its gradation with the size of the blocks so specified that desired screen angles can be achieved in a correct and easy way.
2. Description of the Related Art
Known in the art of multi-color imagery is a method in which data that represents the gradation levels for each of the colors the image is to be recorded in and which are input to an image forming apparatus is divided into blocks each consisting of predetermined regions and the gradation levels of individual pixels are converted within each block on the basis of a transformation matrix having tone conversion characteristics set in correspondence with the position in the block so as to accomplish graduated recording.
If the same transformation matrix is applied to all of the colors in which the image is to be recorded, image deterioration occurs as exemplified by moirès due to interference between recording colors or the clogging up of colors that are placed in the same position. To avoid these problems, multi-color images are recorded using transformation matrices that have different screen angles for the respective recording colors.
However, the transformation matrices having different angles for different colors are not necessarily square in shape and it is often required to set matrices of complex shapes. With a square matrix, blocks into which the data for image's gradation levels are to be divided need be simply tiled; on the other hand, the transformation matrices having different screen angles for different colors have to be set as those of special shapes so that they have a two-dimensional periodicity and can form the desired screen angles. This setting process requires not only high skill but also a great number of steps to be performed.
SUMMARY OF THE INVENTION
The present invention has been accomplished under these circumstances and has as an object providing an image forming apparatus that enables the formation of high-quality multi-level images by ensuring that the size of blocks into which the image is to be divided is specified in accordance with the resolution of the image to be recorded.
The stated object of the invention can be attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relation:
(55/
n
)<
X/p
<(65/
n
), provided
p
is an integral multiple of 10;
where X is the resolution of the image to be recorded in a given direction and expressed in dpi, p is the length of each block in said given direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying the relation of (55
)<X/p<(65
), provided p is an integral multiple of 10. As a result, blocks that provide a screen angle of about 15 or 75 degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The stated object of the invention can be also also attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relation:
(110/
n
)<
X/p
<(130/
n
), provided
p
is an integral multiple of 5;
where X is the resolution of the image to be recorded in a given direction and expressed in dpi, p is the length of each block in said given direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying the relation of (110
)<X/p<(130
), provided p is an integral multiple of 5. As a result, blocks that provide a screen angle of about 45 degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The stated object of the invention can be also attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relations:
(36/
n
)<
X
1
/p
1
<(44/
n
)
and
(72/
n
)<
X
2
/p
2
<(88/
n
), provided
p
1
and
p
2
are each an integral multiple of 15;
where X
1
is the resolution of the image to be recorded in a given direction and expressed in dpi, p
1
is the length of each block in said given direction and expressed in dots, X
2
is the resolution of the image to be recorded in a direction generally perpendicular to said given direction and expressed in dpi, p
2
is the length of each block in said perpendicular direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying both the relation of (36
)<X
1
/p
1
<(44
) for a given direction and the relation of (72
)<X
2
/p
2
<(88
) for a direction generally perpendicular to said given direction, provided p
1
and p
2
are each an integral multiple of 15. As a result, blocks that provide a screen angle of about 30 degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The stated object of the invention can be also attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relations:
(77/
n
)<
X
1
/p
1
<(94/
n
)
and
(154/
n
)<
X
2
/p
2
<(189/
n
), provided
p
1
and
p
2
are each an integral multiple of 7;
where X
1
is the resolution of the image to be recorded in a given direction and expressed in dpi, p
1
is the length of each block in sai

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