University of Washington

Hain-Ching H Liu

Gregory L Zick

Florence H Sheehan

Analysis of video data in an MPEG compressed format to identify scene changes to facilitate indexing to access specific video frames and to improve data compression and/or quality of the compressed video. MPEG compressed video data include I-pictures, P-pictures, and B-pictures. Scene changes are identified by analyzing P-pictures using average error power, based upon direct cosine transform components in the compressed data, and/or using an interframe correlation between a P-picture and its past reference frame. When a scene change occurs, average error power becomes large and interframe correlation between frames becomes substantially zero. Alternatively (or in addition), B-pictures in a video slot can be analyzed, in terms of interframe correlation between past and future reference frames, using either an AND analysis technique or an OR analysis technique. The AND analysis identifies a scene change when two or more B-pictures between two reference frames defining the video slot all imply a scene change, while the OR analysis indicates that a scene change has not occurred in the video slot if one B-picture implies that a scene change has not occurred. Once the scene changes have been identified, all I-pictures not occurring at a scene change are converted to P-pictures, and all P-pictures immediately following a scene change are converted to I-pictures. This step improves compression and/or quality of the compressed video, since P-pictures require less data than do I-pictures, and fewer I-pictures will be used in the compressed data following this step.

Automatic scene decomposition and optimization of MPEG compressed video

A method and system for identifying end systole and end diastole frames within an angiography sequence. A plurality of images produced during an angiography sequence are digitized, producing digital image data in which gray scale values for each of the pixels in the images are represented. The digital image data are input to a computer (48) to determine the frames in which the coronary arteries are most visible. The coronary arteries are made visible in the images by injecting a radio-opaque contrast substance into the arteries. The frames that occur a end diastole are preferred for diagnostic analysis because the arteries are distended, spread apart from each other, and moving very slowly. To identify such frames for further analysis, the total length of edges within a centered window covering approximately one-fourth of each image is determined. The edges represent spatial transitions between relatively light and dark areas in the image that occur across the borders of the coronary arteries. At end diastole during the cardiac cycle, the total length of the coronary arteries within the window is substantially less than at end systole, when the heart has contracted to a minimum volume. Frames in which a local maximum total edge length is observed thus depict the arteries at end systole. Similarly, frames having a local minimum total edge length show the arteries at end diastole. Either a spatial method or a discrete cosine transform (DCT) method is used for determining the total edge length in each frame.

Growing community of inventors

Seattle, WA, United States of America

Hain-Ching H Liu