Image analysis – Image enhancement or restoration
Reexamination Certificate
1995-05-31
2001-08-21
Couso, Jose L. (Department: 2621)
Image analysis
Image enhancement or restoration
Reexamination Certificate
active
06278803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an interpolation equipment for pictorial signals, etc., which have been obtained by offset sampling.
2. Related Background Art
Conventionally, a method called offset sampling has been known as a method to compress the band or reduce information amount in the recording and transmission of various kinds of information signals such as image signals.
This offset sampling, in the case of two dimensions, is such that as shown in
FIG. 1
, the sampling interval (Tx, Ty) between the horizontal direction (x direction) and the vertical direction (y direction) is set twice the pixel interval at the original signals (Hx, Hy) and at the same time the adjacent points of sampling in the vertical direction are offset by one-half the sampling interval (Tx/2). The transmission band by the offset sample can be made wider, as shown in
FIG. 2
, in terms of spatial frequency component in the horizontal or vertical direction against the spatial frequency of a diagonal direction. Also, in case the image signal of the above offset sampling is displayed on the monitor or printed out, it is necessary, as shown in
FIG. 3
, to give interpolation processing for interpolating pixels at each sampling point (interpolation pixel) with adjacent pixels. Such interpolation processing functions as a spatial filter which allows the passing of frequency components in the shaded part of FIG.
2
and also inhibits the passing of frequency components in the area containing a turning back point A. This interpolation processing is positioned as in after-filter in the sampling theory.
Meanwhile, such an offset sampling as mentioned above is a very effective method if the prefilter before the sampling is correctly positioned, namely if a sufficient band limitation is made. However, if the pre-filter positioning is not appropriate owing to, for example, hardware limitation or if the pre-filter is not given thoroughly to widen the transmission band, there arises a problem of image deterioration owing to the generation of turning back distortion.
In other words, if the offset sampling is made when the pre-filter is insufficient, the high-area component of the original signal in the horizontal direction, as shown in
FIG. 4A
, turns back as a high-area component of the vertical direction and at the same time, as shown in
FIG. 4B
, the high-area component of the vertical direction turns back as the high-area component of the horizontal direction.
For this reason, the offset sampling is made as shown in
FIG. 5B
without sufficient band limitation of pictures containing the linear portion as shown in FIG.
5
A. Even if the above-mentioned interpolation processing is made to the sampling signal containing this turning-back component, the high-area component at the original signal and the high-area component of the turning back cannot be separated, so that the turning-back distortion cannot be removed entirely. Thus, there arises uneveness of shade or blot on the linear part as shown in
FIG. 5C
, resulting in pictorial deterioration of an output picture.
Accordingly, an adaption-type interpolation method has generally been known as a method to mitigate the generation of the above turning-back distortion.
This adaption-type interpolation method detects, in the interpolation processing of the sampled image signals, whether the interpolation should be started with the pixels of the horizontal direction, whether it should be the pixels of the vertical direction or whether all of the surrounding pixels should be interpolated. Based on the result of this detection, spatial filters having such characteristics as shown in
FIGS. 6A-6C
are used selectively to remove unnecessary turning-back components. In this event, if the interpolation pixels are those constituting the linear line of the horizontal direction, filters having such characteristics shown in
FIG. 6A
as allowing more frequency components of the horizontal direction to pass through, are used to filter (remove) frequency components of the vertical direction containing turning-back components.
Incidentally, in the case of the above adaption-type interpolation method, the accuracy of judgment to select interpolation means determines the performance of the interpolation equipment.
In other words, if the occurrence of false judgment has high probability, there was a problem in that the interpolation processing based on false detection not only reduced original signal components but also resulted in the increase of turning-back distortion.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and seeks to offer the interpolation equipment of the offset sampling signals which allows the prevention of the generation of turning-back distortion by detecting accurately the “tendency” of surrounding pixels centering on interpolation pixels.
To attain this objective one embodiment of the present invention offers interpolation apparatus for offset sampling signals, comprising a plurality of interpolation means having different interpolation methods respectively and selection means for selecting one of outputs of the plurality of interpolation means according to degree of correlation between a group of pixels consisting of pixels located in the surrounding area of an interpolation pixel and a plural number of other groups of pixels located in the surrounding area of the pixel group.
According to the above embodiment, it becomes possible to conduct interpolation processing, on the basis of accurate judgment of the “tendency” in the pixels interpolation pixels by selecting interpolation means according to the correlation between a group of pixels comprising pixels located in the surrounding area of interpolation pixels and a plural number of other groups of pixels located in the surrounding area of the pixel group.
By so doing, the occurence of turning-back distortion based on the traditional false judgment can be prevented. Consequently, the occurence of deterioration of image quality resulting from the turning-back distortion can be prevented.
Furthermore, to attain this objective, another embodiment of the present invention provides interpolation apparatus for offset sampling, comprising selection means to select one of outputs of the plurality of interpolation means according to degree of correlation between a group of pixels comprising pixels located in the surrounding area of the interpolation pixel and a plural number of other group of pixels located in the surrounding area of the pixel group and a distribution area of each level at a plural number of pixels located in the surrounding area of the interpolation pixel.
According to the present Embodiment it is possible to conduct interpolation processing based on the result of accurate judgment of the “tendency” in the surrounding of interpolation pixels by selecting interpolation means according to the degree of correlation between a group of pixels comprising pixels located in the surrounding area of interpolation pixels and a plural number of other groups of pixels located in the surrounding area of the pixel group.
Consequently, the occurence of turning-back distortion based on the traditional false judgment can be prevented. Thus, the occurence of deterioration of image quality originating from turning-back distortion can be prevented.
Besides, the present invention allows it to detect the “tendency” of changes in the surrounding pattern of interpolation pixels by detecting the distribution range of levels of each pixel data and, based on the result of the detection, to attain interpolation processing which is unlikely to provide false judgment by making at one time the interpolation output on the basis of all surrounding pixels of interpolation pixels of level fluctuation being small.
To achieve this objective, another embodiment of the present invention provides interpolation apparatus for offset sampling of signals comprising a plurality of interpolations means whose interpolation methods are diff
Canon Kabushiki Kaisha
Couso Jose L.
Robin Blecker & Daley
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