Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2001-02-22
2003-07-01
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C382S173000, C382S174000
Reexamination Certificate
active
06587115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of an apparatus for distinguishing the types of pixels making up an original, and more particularly to a method of and an apparatus for distinguishing the types of pixels making up an original, which are used, for instance, in a stencil printer which makes a stencil by image wise perforating a heat-sensitive stencil material and a print is made from the stencil, and a copier or a printer in which a latent image is formed on a photosensitive medium by electrophotography or the like and a toner image obtained by developing the latent image is transferred to a printing paper or a heat-sensitive paper.
2. Description of the Related Art
In the fields of plate making and printing, there has been put into practice a process in which an original, in which binary images such as a line drawing and characters and tone images such as a picture and halftone dots mingle together (such an original will be referred to as a “complex original”, hereinbelow), is read by an image scanner, a multivalued image signal sampled in a main scanning direction and a sub-scanning direction pixel by pixel is obtained, the multivalued image signal is converted into a binary image signal, and a plate or a print is made from the binary image signal.
In order to obtain a desirable output when a complex original is output through an image processing apparatus, generally, the region of the binary image is subjected to a binary image density conversion in which the density of each pixel is converted to a maximum density or a minimum density on the basis of a single threshold value, the region of the tone image is subjected to a tone image density conversion in which the density of each pixel is converted taking into account the properties of the input/output system so that the tone properties of the original image are preserved, and then the region of the binary image is binary-coded by a simple binary-coding method using a single threshold value while the region of the tone image is binary-coded by a pseudo-halftone expressing method such as a dither method and an error diffusion method. The density conversion is carried out on the basis of a density conversion curve (function) and/or LUT (lookup table) exclusive to the type of the image. That is, a density conversion curve and/or LUT exclusive to the binary image are used for density conversion of the region of the binary image and a density conversion curve and/or LUT exclusive to the tone image are used for density conversion of the region of the tone image.
Accordingly, it is necessary to determine the type of each region, that is, to distinguish the binary image region from the tone image region. In other words, it is necessary to distinguish the type of each pixel (the type of image which the pixel makes up) in order to determine the density conversion curve and/or the LUT according to which the density conversion is to be carried out on the pixel. There have been proposed various methods of distinguishing the binary image region and the tone image region from each other.
For example, in Japanese Unexamined Patent Publication No. 5(1993)-114045, a method of distinguishing the types of images in which an original image is divided into a plurality of blocks each including m×n pixels, properties of the image in each block are detected, and determining which of a binary image, a tone image and a blank (background), the image in each block is on the basis of the properties detected, with the result of the determination being corrected, if necessary, taking into account the properties of the images in blocks near the block.
However, the method gives rise to a problem that when each block is set in a size larger than such a size that the properties of the image therein can be visually determined (will be referred to as “the visually distinguishable size”, hereinbelow), there is a fear that both a region of characters and a region of a picture exist in one block (such a block will be referred to as “a complex block”, hereinbelow). That is, since the image even in a complex block must be determined to be a binary image or a tone image, the result of the determination is inherently partly true and partly not true.
When a density conversion is carried out on pixels in each block on the basis of the result of the determination, the picture region is output to be higher in density when the block is determined to be a binary image block, since a density conversion is carried out on a picture image region by use of the density conversion curve exclusive to the binary image. Conversely, if the block is determined to be a tone image block, the character region is output to be lower in density as compared with when the density conversion is carried out by use of the density conversion curve exclusive to the tone image.
To the contrast when the block is set in a size smaller than the “visually distinguishable size”, it becomes difficult to determine whether an image in each block is a part of a thick character or a high density portion of a picture. Also in this case, the image in each block must be determined to be a binary image or a tone image, the result of the determination is inherently partly true and partly not true.
When a density conversion is carried out on pixels in each block on the basis of the result of the determination, the picture region is output to be higher in density when the block is determined to be a binary image block, since a density conversion is carried out on a picture image region by use of the density conversion curve exclusive to the binary image. Conversely, if the block is determined to be a tone image block, the character region is output to be lower in density as compared with when the density conversion is carried out by use of the density conversion curve exclusive to the tone image.
If the densities of pixels are output to be higher or lower than a correct density due to wrong determination, a density step is generated between a part correctly determined and a part incorrectly determined and the observer feels strange.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a method and an apparatus which can distinguish more precisely the binary image region and the tone image region (can more precisely distinguish the types of pixels) in a complex original, in which binary images and tone images mingle together.
In accordance with the present invention, the original image is divided into a plurality of blocks each being not smaller than “the visually distinguishable size” and the kind of the image in each block is determined on the basis of the properties of the block. The pixels in the block which can be readily determined to be a binary image block by the “block-by-block” determination are all determined to be pixels of a binary image (that is, the pixels are of a binary image type), and, for example, are subjected to density conversion according to the density conversion curve exclusive to the binary image. Similarly, the pixels in the block which can be readily determined to be a tone image block by the “block-by-block” determination are all determined to be pixels of a tone image (that is, the pixels are of a tone image type), and for example, are subjected to density conversion according to the density conversion curve exclusive to the tone image. On the other hand, the types of pixels in the block which cannot be readily determined to be a binary image block or a tone image block by the “block-by-block” determination (will be referred to as “an indeterminate image block”, hereinbelow) are determined pixel by pixel.
That is, in accordance with a first aspect of the present invention, there is provided a method of distinguishing the types of pixels of an image made up of a plurality of pixels arranged in a main scanning direction and a sub-scanning direction comprising the steps of
carrying out a block-by-block determination in which the image is divided
Gong Weidong
Nakajima Masato
Luu Matthew
Nixon & Peabody LLP
Riso Kagaku Corporation
Studebaker Donald R.
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