Image analysis – Image enhancement or restoration – Image filter
Reexamination Certificate
1998-10-29
2001-06-26
Rogers, Scott (Department: 2724)
Image analysis
Image enhancement or restoration
Image filter
C382S264000
Reexamination Certificate
active
06252997
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for image processing in a computer and a computer adapted thereto.
BACKGROUND OF THE INVENTION
One of the methods for expressing a sense of volume or distance is blurring. For example, when a photograph is taken, an object just in focus is taken clear and degree of blurring is greater as the object is more separated from the focus. It is known that this blurring provides a photograph with a sense of distance.
One of the methods for expressing blurring by means of computer is dispersed beam tracing method. Another method to express blurring more simply is a method disclosed in the patent specifications of Toku-Kai-Hei 6-36025 and Toku-Kai-Hei 2-190898 in which the diameter of a blurring circle around each pixel is calculated based on the information of distance for the pixel and, thereby, spreading area of blurring extended to neighboring pixels is determined to show the sense of distance. Calculation of blurring process is carried out with dots of 3 by 3 in Toku-Kai-Hei 2-190898 and with dots of 5 by 5 in Toku-Kai-Hei 6-36025.
Of the methods referred to above, the dispersed beam tracing method requires a lot of time for calculation, such as for calculating on a multitude of beams to build up a blurred image related to one pixel. The method of calculating the effect of neighboring pixels on the pixel of interest can be carried out in shorter period than dispersed beam tracing method but it is associated with other problems.
For example, in the method disclosed in Toku-Kai-Hei 6-36025, the effect of neighboring pixels is taken into account with the use of a kernel of 5 by 5 to accomplish sense of distance, but pixels that can be considered with respect to the latter are those only two pixels remote from the pixel of interest. For calculation of data required to express a pixel, data on a kernel of 25 pixels including neighboring pixels have to be added after processing, resulting in heavy burden of calculation. 25 weight coefficients involved in the kernel have to be calculated for each pixel, thereby the burden of calculation increases. Weight coefficients for dots other than that in the center of the kernel are calculated by the following equation:
fw
i,j
=|(1
−fw
33
)/(5×5−1)|×
df
i,j
The equation above can be transformed as follows:
fw
i,j
=(
df
33
×df
i,j
)/(5×5−1)
This equation indicates multiplication of distance by distance. Therefore, repeating of filter processing seems to be needed, with the times of filtration set to control the degree of blurring. This repeated processing also increases burden of calculation.
In the method of Toku-Kai-Hei 2-190898, effect of surrounding pixels is taken into account based on a mask register of 3×3, but it is the effect of only pixels directly adjacent to the pixel of interest that can be dealt with. Moreover, addition of data on mask registers of 9 pixels including surrounding pixels subsequent to the processing is required to accomplish the calculation of data for expressing a pixel of interest. In this method, it is rather easy to select a suitable mask register based on the distance information but it is difficult to design the contents of mask register (weight coefficients) in accordance with the distance.
For a very far object, the effect of pixels remote as much as 10 pixels from the pixel of interest may contribute in view of characteristics of human vision. To encounter such an effect, the mask register has to be extended to 21×21, thereby addition of data on a mask register of 441 pixels consisting of surrounding pixels subsequent to the processing is required to calculate the data for expressing blurring of a pixel of interest, resulting in an unreasonable burden of calculation. A remarkable difficulty is expected to arise also in designing the contents of masks register in accordance with distance. Thus, real expression of sense of distance is limited in practical application of the method.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a method for processing image data capable of expressing sense of distance with more reality by blurring of the image and improved in the efficiency of processing, whereby the burden of calculation is decreased.
It is another object of the invention to provide a method for processing image data capable of expressing sense of distance by blurring of the image having compatibility with a conventional rendering system.
It is still another object of the invention to provide a digital computer adapted to the method for processing image data capable of expressing sense of distance with more reality by blurring of the image.
According to the invention, a method for processing image data having far and near distance information comprises the step of:
generating images including a blurred image in accordance with the far and near distance information by applying image processing by a digital low pass filter to the image data;
wherein the digital low pass filter has a cut-off frequency corresponding to the far and near distance information.
According to the invention, a method for processing image data having far and near distance information of images preferably comprises the step of:
generating a blurred image based on an image selected from the images by applying image processing by a digital low pass filter to the image data of the selected image to remove higher frequency components therefrom;
wherein the digital low-pass filter has a cut-off frequency lower than the highest frequency of frequency components in the image data of the selected image, represented by the formula;
f
d
=kf
m;
f
d
representing the cut-off frequency, f
m
representing the highest frequency of frequency components in the image data to be processed contain and k representing a positive variable less than 1.
According to the invention, a digital computer in which image data having far and near distance information are processed so as to generate images including a blurred image comprises: a digital low-pass filter for generating the blurred image based on the far and near distance information, having a cut-off frequency represented by the formula:
f
d
=kf
m
:
f
d
representing the cut-off frequency, f
m
representing the highest frequency of frequency components in the image data to be processed and k representing a positive variable less than 1; and
a medium for recording a program to execute the process to generate the images including the blurred image. information means the information of distance between the object and the observer, including a camera such as still camera, TV camera etc.
The effect of blurring is determined by controlling the highest frequency of frequency components contained in the distance information of the image. Concerning the control, the present invention permits assignment of the distance to a blurred image freely and quantitatively by approximating the characteristics of human vision by a digital filter having frequency characteristics in accordance with the distance information of the blurred image.
The cut-off frequency f
d
of a digital low-pass filter used in the invented method is determined in relation to the highest frequency f
m
of frequency components which the original image contain, by the following equation:
f
d
=kf
m
:
where k is a positive variable not larger than 1. The variable k is the reciprocal of the ratio of the number of dots in the processed image of minimum discernible dimension to the number of dots in the original image of minimum discernible dimension.
REFERENCES:
patent: 10074258 (1998-03-01), None
patent: 1056050 (2000-11-01), None
patent: 1063616 (2000-12-01), None
Goto Hidemichi
Miura Takashi
Hudson Soft Co. Ltd.
Rogers Scott
Scully Scott Murphy & Presser
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