Television – Monitoring – testing – or measuring – Testing of image reproducer
Reexamination Certificate
1998-02-27
2001-09-25
Eisenzopf, Reinhard J. (Department: 2614)
Television
Monitoring, testing, or measuring
Testing of image reproducer
C348S180000, C348S181000, C348S189000, C348S263000, C382S294000, C382S151000
Reexamination Certificate
active
06295083
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to digital video test and measurement, and more particularly to high precision image alignment detection for the registration of two images.
Conventional measurement of video signals occurs in the analog, broadband domain using conventional waveform monitors and vectorscopes. As video signals move into the digital domain, using serial digital formats and compression, the digital signals are conventionally converted into the analog, broadband domain for typical video measurements. However, especially with compressed video signals, there are additional requirements on the measurement of video signals since an important aspect of compression/decompression techniques is to assure a controlled level of picture quality degradation, i.e., the decompressed video signal presents the expected quality of display related to the video signal prior to compression.
The PQA200 Picture Quality Analysis System, manufactured by Tektronix, Inc. of Wilsonville, Oreg., is a programmable instrument for automatic measurement of compressed video quality, and is described in allowed U.S. patent application Ser. No. 08/605,241 filed Feb. 12, 1996 by Bozidar Jenko et al. The PQA200 adds stripes and registry marks to the active video portion of the video signal so that, when the video signal is compressed and then decompressed, the images in the received, decompressed video signal may be aligned with the corresponding images in the video signal prior to compression. The precision of this alignment process is important to provide the most accurate determination of picture quality.
What is desired is a high precision image alignment detection technique to assure that corresponding images to be measured for picture quality are aligned to provide the most accurate determination of picture quality.
BRIEF SUMMARY OF THE INVENTION
Accordingly the present invention provides high precision image alignment detection for providing high precision registration of two corresponding images. The detection is a four stage process, with the first two stages being used to locate an alignment pattern in a received image by cross-correlation with a reference image corresponding to the alignment pattern. This detects an integer pixel shift +/−0.5 pixel. Selected lines from the received alignment pattern are then used together with the reference image to perform a part pixel shift determination in the next two stages. The first of these stages determines an initial part pixel shift, and then the final stage does a fine part pixel shift determination in an iterative manner using a cross-correlation to redetermine the integer pixel shift and successive shifts and measurements based upon prior measurements to refine the part pixel shift as accurately as desired. The final pixel shift, which represents the misalignment between the received image and the reference image, is the sum of the integer pixel shift and the part pixel shift.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.
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Desir Jean W.
Eisenzopf Reinhard J.
Gray Francis I.
Tektronix Inc.
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