Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1996-07-26
2001-12-11
Lee, Cheukfan (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S523000, C358S518000
Reexamination Certificate
active
06330075
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image processing method and apparatus. More particularly, the invention relates to color reproduction processing of a color printer.
An image processing method based upon a color dot model is well known as an image processing method using a color printer.
FIG. 20
is a block diagram illustrating the architecture of an image processor in a color printer according to the prior art. The luminance signals of R, G, B entered from an input terminal
101
are each converted to density signals of C, M, Y by a density converter
102
. A black density signal K is produced by a black generator
103
from the density signals resulting from the conversion, and a dot area signal subjected to undercolor removal and compensated for crosstalk components of the density signals by a masking/UCR unit
104
is obtained. Linearity between the dot area signal and output density based upon dot gain is corrected by an output gamma corrector
105
, each color component is binarized by a binarizing unit
106
, and the resulting dot patterns are outputted to a printer engine (not shown) from an output terminal
107
.
The density converter
102
and output gamma corrector
105
usually are constituted by a look-up table (hereinafter referred to as a “LUT”).
In the example of the prior art described above, binarization processing is executed for each of the C, M, Y, K planes. Consequently, the overlapping of the C, M, Y, K dots is random, it is very difficult to achieve conformity of color reproduction by masking and difficult to limit the number of dots on dots.
Further, since density conversion, black generation, masking/UCR, output gamma correction and binarization processing are executed independently of one another, processing takes time or a large amount of hardware (calculations) is required.
The specifications of U.S. Pat. Nos. 5,070,413 and 5,270,808 describe technology for converting input color image data to output color image data in three-dimensional color space. The disclosed technology obtains 1-bit output data for each of Y, M, C, K from 8-bit input data for each of R, G, B. According to this approach, in order to determine which output color, among 16 output colors represented by one bit for each of Y, M, C, K, the input data represented by eight bits for each of R, G, B in three-dimensional color space is nearest to, 16 distances between the input data and the output colors are obtained and the output color for which the distance is smallest is decided upon as being the output color.
In this case, processing takes time. Accordingly, there is a need for high-speed processing and processing for providing higher image quality.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image processing method and apparatus through which high-speed processing and a high-quality color image can be obtained.
Another object of the present invention is to provide an image processing method and apparatus through which each of a plurality of input color-component data is converted to data having a level lower than the input level, a table is accessed by data the amount of which has been reduced and a plurality of output color-component data are generated, thereby making it possible to obtain a high-quality color image simply and at high speed.
According to the present invention, the foregoing objects are attained by providing an image processing method comprising an input step of entering data of a plurality of color components in input color space, a quantization step of quantizing the data of each of the plurality of color components to data having a level lower than an input level, a generation step of generating data of a plurality of output color components, by a table conversion, from the quantized data of the plurality of color components, a step of obtaining color reproduction error between input color data and output color data by converting colors, which are expressed by the data of the plurality of output color components, to data in the input color space, and a first error correction step of correcting the color reproduction error obtained.
Further, according to the present invention, the foregoing objects are attained by providing an image processing apparatus comprising input means for entering data of a plurality of color components in input color space, quantizing means for quantizing the data of each of the plurality of color components to data having a level lower than an input level, generating means for generating data of a plurality of output color components, by a table conversion, from the quantized data of the plurality of color components, means for obtaining color reproduction error between the input color data and output color data by converting colors, which are expressed by the data of the plurality of output color components, to data in input color space, and first error correction means correcting the color reproduction error obtained.
A further object of the present invention is to provide an image processing method and apparatus for generating a plurality of output color-component dot patterns from a plurality of input color-component data, thereby making it possible to obtain, simply and at high speed, a high-quality color image having a resolution higher than the input resolution.
According to the present invention, the foregoing object is attained by providing an image processing method comprising an input step of entering data of a plurality of input color components in input color space, a generation step of generating dot patterns of a plurality of output color components, by a table conversion, based upon the data of the plurality of input color components, a step of obtaining color reproduction error between input color data and output color data by converting colors, which are expressed by the dot patterns of the plurality of output color components, to data in the input color space, and a first error correction step of correcting the color reproduction error obtained.
Further, according to the present invention, the foregoing object is attained by providing an image processing apparatus comprising input means for entering data of a plurality of input color components in input color space, generating means for generating dot patterns of a plurality of output color components, by a table conversion, based upon the data of the plurality of input color components, means for obtaining color reproduction error between input color data and output color data by converting colors, which are expressed by the dot patterns of the plurality of output color components, to data in the input color space, and first error correction means for correcting the color reproduction error obtained.
Yet another object of the present invention is to provide an image processing method and apparatus for generating an output dot pattern directly from input pixel data using a LUT obtained by partitioning input color space into a predetermined number of zones and mapping an output dot pattern for each zone of partitioned space, converting the output dot pattern to input color space using a LUT that converts a color reproduced by the output dot pattern to input color space, obtaining the difference (error) with respect to the input pixel data, and diffusing the difference value to neighboring pixels, whereby color reproduction and binarization processing are executed by a search of the two LUTs and a single error-diffusion processing step to obtain, in simple fashion, an image output exhibiting good color reproduction, wherein the number of dot-on-dot mixed colors of C, M, Y, K is strictly limited owing to the fact that the CMYK dot pattern is mapped.
A further object of the present invention is to provide an image processing method and apparatus in which processing for diffusing error due to density conversion and quantization is executed in RGB luminance space and color-reproduction error-diffusion processing is executed in output density space, whereby error diffusion is performed in the ideal space
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Cheukfan
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