Image analysis – Image transformation or preprocessing – Changing the image coordinates
Reexamination Certificate
1999-09-30
2003-07-22
Couso, Yon J. (Department: 2625)
Image analysis
Image transformation or preprocessing
Changing the image coordinates
C358S525000
Reexamination Certificate
active
06597819
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for carrying out an interpolation operation on original image data comprising pixels each including a channel representing transparency and channels representing color or density, and also to a computer-readable recording medium storing a program to cause a computer to execute the interpolation operation method.
2. Description of the Related Art
Enlargement reproduction or reduction reproduction of image data obtained by photoelectrically reading an image recorded on a film or by photographing a subject with a digital camera has been carried out. Such enlargement or reduction of image data has been carried out by obtaining interpolated image data having pixel spacing different from that of original image data through an interpolation operation on the original image data. As the interpolation operation, high-degree interpolation operations, such as the cubic spline interpolation operation generating a sharp interpolated image and the B spline interpolation operation generating a comparatively smooth interpolated image, or linear interpolation operations are used.
Meanwhile, image data are RGB or RGB&agr; data defined as a 3-channel or 4-channel image respectively. Especially, the &agr; channel in the RGB&agr; image data defines transparency at a pixel in the original image represented by the image data. Depending on the value of the &agr; channel, a composition ratio of the image data and a mount image which the image data are printed on or inserted in is changed. More specifically, the smaller the a value is, the more the mount becomes visible through the image. By changing the &agr; channel value near the border between the original image and the mount to a small value, the image is composed with the mount as if the image is blended into the mount. For example, as shown in
FIG. 6
, when pixels each having values of R=G=B=255 (&agr;=0), R=G=B=33 (&agr;=1), and R=G=B=33 (&agr;=1) are pasted on a black mount (R=G=B=0), the pixel values are changed according to the &agr; channel value, based on the following Equation (1) below:
P=F
2
×(1−&agr;)+
F
1
×&agr; (1)
where P is a value of a pixel pasted on the mount,
F
1
is a value of a pixel of the image to be pasted on the mount, and
F
2
is a value of a pixel of the mount at the position corresponding to the pixel value of the image.
As shown in
FIG. 7
, the image is then pasted on the mount in such a manner that only the pixels whose &agr; value is 1 remain.
As has been described above, when the transparency is defined by the &agr; channel, an image can be blended into a mount and the image and the mount can be composed together in a more natural manner.
It is also possible to enlarge or reduce an original image by carrying out an interpolation operation on image data having the &agr; channel. For simplicity, let's take an example of enlarging image data by 2 through linear interpolation. The RGB values and the &agr; channel value of the pixels shown in
FIG. 6
are RGB=255 (&agr;=0) (hereinafter, for simplicity, an expression “RGB=n” is used for the case of R=G=B=n where n is a number), RGB=144 (&agr;=0.5), RGB=33 (&agr;=1), RGB=33 (&agr;=1), and RGB=33 (&agr;=1), as shown in FIG.
8
. In
FIG. 8
, the pixels augmented as a result of interpolation are shown as black dots. When the image data interpolated as has been described above are pasted on the black mount, the values of each pixel are changed according to the &agr; channel value, based on Equation (1), and an image having the pixel values shown in
FIG. 9
is pasted onto the mount.
However, when the image data having the &agr; channel are interpolated, a portion where pixel values are larger than those of surrounding pixels, such as RGB=72, is generated at a border where the &agr; channel value changes from 1 to 0, as shown in FIG.
9
. As a result, a white streak is generated at the border between the pasted image and the mount. In order to prevent such white streaks from occurring, a linear interpolation method (hereinafter called the pre-multiplied &agr; method) can be used.
In the pre-multiplied &agr; method, the RGB values of each pixel are multiplied by the &agr; channel value in advance. In other words, the second term of Equation (1) is found in advance. The 4 channels, namely &agr;, &agr;R, &agr;G, and &agr;B are then linearly interpolated In this method, the 3 values (&agr;R, &agr;G, and &agr;B) of the pixel shown in
FIG. 6
become RGB=0, RGB=33, and RGB=33, as shown in FIG.
10
. When enlargement by 2 is carried out, the values become RGB=0 (&agr;=0), RGB=16 (&agr;=0.5), RGB=33 (&agr;=1) , RGB=33 (&agr;=1), and RGB=33 (&agr;=1) . When an image having such pixel values is pasted onto the same black mount, no white streak is generated near the border where the &agr; value changes from 1 to 0, since RGB=0 (&agr;=0), RGB=16 (&agr;=0.5), RGB=33 (&agr;=1), RGB=33 (&agr;=1), and RGB=33 (&agr;=1), as shown in FIG.
11
.
As has been described above, interpolation of image data having the &agr; channel can be carried out easily by adopting linear interpolation, although linear interpolation has a drawback such that it tends to create a blurry interpolated image. Therefore, in order to increase sharpness, high-degree interpolation operations such as the cubic spline interpolation and the B spline interpolation are carried out on the image data having the &agr; channel.
In the case where a high-degree interpolation operation is carried out in order to improve sharpness as has been described above, image data after interpolation (interpolated image data) do not have monotonically increasing or decreasing data as in the case of linear interpolation. However, the interpolated image data have more or less over shoot or under shoot occurring at a border such as an edge included in the image. Such over shoot or under shoot brings preferable visual effects to an image. However, if a high-degree interpolation operation is carried out on image data having the &agr; channel, an image of the mount can be seen at some portions where the &agr; channel value changes, or cannot be seen at other portions where the &agr; channel value also changes. In this manner, an artifact is created. In this case, it is possible to carry out a linear interpolation operation only on the &agr; channel and to carry out a high-degree interpolation operation on the other channels. However, the &agr; channel would not be harmonious with the other channels in this case and an artifact is also created.
SUMMARY OF THE INVENTION
The present invention has been created based on consideration of the above problems. An object of the present invention is to provide a method and an apparatus for obtaining an interpolated image having high sharpness and no artifact from image data having the &agr; channel, and a computer-readable recording medium storing a program to cause a computer to execute the interpolation operation method.
An interpolation operation method of the present invention is an interpolation operation method of finding interpolated image data having pixel spacing different from that of original image data by interpolating the original image data comprising pixels each having a channel representing transparency and channels representing color or density, and the interpolation operation method comprises the steps of:
carrying out an interpolation operation different for each interpolation point, depending on the values of the channel representing transparency of all pixels in a predetermined area surrounding the interpolation point in the original image represented by the original ima
Birch & Stewart Kolasch & Birch, LLP
Couso Yon J.
Fuji Photo Film Co. , Ltd.
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