Image analysis – Applications – Motion or velocity measuring
Reexamination Certificate
1998-02-10
2001-12-11
Johns, Andrew W. (Department: 2721)
Image analysis
Applications
Motion or velocity measuring
C382S236000
Reexamination Certificate
active
06330344
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to image processing, and in particular, to an image processing device and method for reducing aliasing distortion due to undersampling of an image. The invention also relates to a technique for generating a high resolution image by increasing the number of pixels of a low resolution image.
With modern digital imaging techniques, analog video signals are sampled and stored as digital data for subsequent reproduction on a cathode ray tube (CRT) or other display. It is a design goal to display such images with as high a resolution and as little distortion as possible.
Images displayed on a CRT, such as images derived from television signals, video tape recorders (VTRs) or from digital versatile disc (DVD) players, are generated by repetitive scanning of electron beams in the horizontal direction. As illustrated in
FIG. 25.
, each horizontal scan is performed from left to right, and after each scan, the beams are swept back to the extreme left and re-positioned vertically to commence the next horizontal scan. The fluorescent screen of the CRT is irradiated by three electron beams to illuminate respective blue, green and red phosphors distributed in small units on the screen. The phosphors produce points of light corresponding to the intensity of the electron beams, and the congregation of all the points produces an image. Hence, a displayed image can be considered a congregation of such points, that is, pixels.
Since a displayed image on a CRT derived from an analog signal is composed of a congregation of light emitting pixels, the image can be envisioned as a digital signal obtained by sampling the original image at the pixel positions. Thus, if the original analog image were sampled at a sufficient sampling interval in both horizontal and vertical directions to generate the same number of points as the number of pixels on a CRT, a collection of image data could be stored digitally. When subsequently reproduced, an image of nearly the same resolution is obtained as in a strictly analog recording/reproduction approach.
The sampling theorem dictates that an analog signal can be reconstructed completely from a set of uniformly spaced discrete samples thereof in time, provided that the signal is sampled at a rate of at least twice the highest frequency component of the signal. When sampling an original image, if the sampling theorem is not satisfied, aliasing distortion is generated in the displayed image. To correct for aliasing distortion, prefilters have been used to compensate for undersampling in the horizontal (scanning line) direction; however, such prefilters are not typically provided in the vertical direction. As such, aliasing distortion in the vertical direction is a common problem.
FIG. 26
illustrates aliasing distortion of a displayed image in the vertical direction. Four pixels P
1
-P
4
of a given column are shown in each of frames N and N+1. Signals S
N
and S
N+1
represent the image level variation of the original image in the vertical direction for the given column, where the amplitude level is illustrated horizontally in the figure. Thus, for example, in frame N, the luminance of the image is higher for pixel P
2
than for pixel P
1
. Now, if the highest spatial frequency component of the original image in the vertical direction has a period of less than twice the horizontal spacing between pixels, then the sampling theorem is not satisfied and aliasing distortion results. Such is the case for both signals S
N
and S
N+1
in FIG.
26
. For instance, signal S
N
′, which is an approximation for the sampled signal of frame N, is markedly different from the original signal S
N
. With the aliasing distortion, the high frequency component of the original signal will be lost during reproduction, even if a filter to remove aliasing is employed in the vertical direction. Such aliasing distortion may be a cause of degradation in signal processing such as Y/C separation, noise removal, quality improvement, and so forth.
It is noted that while undersampling of the image as just discussed will always result in diminished resolution, the effect on the viewer in terms of picture quality depends on how the scene changes from frame to frame. If a frame with aliasing distortion changes significantly from frame to frame, as is the case in
FIG. 26
, then an unnatural moving image or blurring results from the perspective of the user. If the scene remains still, the aliasing noise is not as great. In any event, since resolution is always degraded by undersampling, and since the signals of standard television broadcasts and the like are intended for only a limited number of horizontal sweeps per frame, there is a need for a practical way to remove aliasing and recapture the original image with improved quality.
OBJECTS AND SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a way to convert an undersampled image signal into an output image signal with aliasing distortion reduced or eliminated.
It is another object of the invention to generate a high resolution image from a low resolution image.
It is yet another object of the invention to improve the quality of a displayable image generated from a low quality input image signal.
Various other objects and advantages of the invention will become readily apparent to those of ordinary skill in the art, and the novel features will be particularly pointed out in the appended claims.
In an illustrative embodiment of the invention, there is provided an image signal converting apparatus for converting a first image signal into a second image signal, where the first and second image signals each include a plurality of pictures of different frames. The apparatus includes a motion detector operable to detect motion of the first image signal between a first frame and a second frame, and processing circuitry for producing the second image signal based on an assumption of a pixel at a position corresponding to the detected motion.
The apparatus may be employed to produce an output signal of either the same resolution as the first image signal with aliasing distortion reduced or eliminated, or with higher resolution in vertical and/or horizontal directions. The motion detector preferably detects the motion of the first image signal by a finer amount than a pixel size of the first image signal. The processing circuitry may be composed of a resolution creating memory for storing a picture of the first image signal and having a larger storage capacity than an amount of data within one picture of the first image signal, and a controller operable to control writing of the first image signal into the resolution creating memory and reading of a new image signal from the memory. The controller writes the first image signal in the memory in accordance with the detected motion of the first image signal.
In another embodiment, the image converting apparatus includes an area divider for defining at least first and second image areas of a picture, where motion is detected in each of the image areas. In this case, first and second image areas of the second image signal are generated based on an assumption of pixels at positions corresponding to the detected motion in the respective first and second image areas of the first image signal. A combiner combines the first and second image areas of the second signal to generate a composite image.
In one application, the first image signal may be a standard definition (SD) image signal which is converted to a high definition (HD) image signal as the second image signal having twice the resolution of the SD signal in both the horizontal and vertical directions. For some of the frames, pixels of the HD signal may also be generated by an adaptive processing technique.
REFERENCES:
patent: 5111511 (1992-05-01), Ishii et al.
patent: 5367340 (1994-11-01), Spencer
patent: 5381183 (1995-01-01), Ishizuka et al.
patent: 5485611 (1996-01-01), Astle
patent: 5517588 (1996-05-01), Kondo
patent: 5557298 (1996-09-01),
Kondo Tetsujiro
Ohtsuki Tomoyuki
Watanabe Tsutomu
Azarian Seye D.
Frommer William S.
Frommer & Lawrence & Haug LLP
Johns Andrew W.
Savit Glenn F.
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