Method and system using non-uniform image blocks for rapid interactive viewing of digital images over a network
Apparatus and method for rapid interactive viewing of a digital image over a network. A client computer displays a view of an image. The image is originally resident on a server computer. The client computer maintains a cache, initially empty, of image blocks already obtained from the server. When the client computer is asked to render a view of a particular portion of the image at a particular resolution, it first ascertains if any image blocks in the image-block cache intersect the requested view. It then computes the residual area of the view resulting from subtracting out from the view the intersecting portions of cached image blocks, and, if the residual area is positive, downloads from the server computer a set of image blocks comprising the residual portion of the view at the given resolution.
1. A method for communicating a digital image over a network, comprising the steps of:
storing a digital image on a server computer;
maintaining on a client computer stored image blocks comprising portions of said digital image that have been downloaded from the server computer to the client computer;
in response to a request by a user of the client computer for a given view, comprising a particular image portion at a given resolution, performing the steps of
computing the residual area of the view resulting from subtracting out from the view the intersecting portions of stored image blocks, and, if the residual area is positive,
downloading from the server computer the residual portion of the view at the given resolution;
partitioning the residual portion of the view into the minimum possible number of rectangles and downloading these rectangles from the server computer, wherein the operation of partitioning the residual portion of the view into the minimum possible number of rectangles comprises recursively executing, for the initial view and each subsequent subview, a procedure that tries to find a first stored image-block intersecting the view, and, if one is found, partitions the residual area of the view into the minimum possible number of rectangular subviews, and, if none is found, treats the entire view as a rectangle to be downloaded from the server computer.
2. A method according to claim 1 , further comprising the step of displaying the given view to the user.
3. A method according to claim 1 , further comprising the step of placing the downloaded image portion in the client computer's image-block cache.
4. A method according to claim 3 , further comprising the step of selectively removing items from the client computer's image-block cache when the size of the cache reaches a limit.