Image analysis – Image compression or coding – Pyramid – hierarchy – or tree structure
Reexamination Certificate
2000-10-25
2001-09-11
Johnson, Timothy M. (Department: 2623)
Image analysis
Image compression or coding
Pyramid, hierarchy, or tree structure
C348S441000
Reexamination Certificate
active
06289132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates generally to digital image signal processing, and more particularly to the compression of interlaced motion images.
2. Description of the Related Art
Image and motion image signals are increasingly being processed in the digital domain. One set of problems encountered in digital image signal processing result from signal formats used in conventional analog video processing. For example, certain formats, particularly conventional broadcast television, implement signal interlacing. In video interlacing, a frame is comprised of two separate rasters. A first raster comprises a series of lines in the frame, and a second raster comprises scan lines that reside between the lines from the first raster. The first and second rasters can respectively be referred to as first and second fields. Thus the video signal can be said to include a series of frames, with each frame including first and second interlaced fields.
There are various problems introduced by interlaced motion images and the conventional processing methods. For example, interlaced images may have relative motion between the rasters, which does not correlate well vertically. One solution to this could be to encode images with significant motion by frame. However, this would result in very inefficient encoding.
Alternatively, images can be processed by field to allow for poor vertical correlation in the case of motion. However, if this is done, the encoding advantage of any high correlation in still areas is lost, again resulting in inefficient encoding. Additionally, if images are processed by field, slight variations in DC errors or quantifier linearity will cause horizontal stripes in a motion free fame viewed as a still.
Typically, block based compression schemes (such as MJPEG and MPEG) treat the interlaced video decorrelation problem on a block level. Thus, each block in a frame is classified as a motion block or a still block. The still image blocks are processed differently from the motion blocks.
There are various problems with the block based approach. Particularly, block based motion analysis can generate boundaries and visual artifacts due to incorrect motion estimation decisions. Also, block based motion analysis can generate very large local errors, making it unsuitable for applications where local error bounds are desired, as in medical, technical or critical production applications. Finally, the block based approach can cause an obvious discontinuity or defect where an object in motion spans adjacent blocks, particularly where one block is still processed while an adjacent block is motion processed.
Thus, there remains a need for digital image signal processing, particularly processing incorporating lossy compression, that addresses the problems introduced by frames having interlaced fields.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for optimized compression of motion images having frames with interlaced first and second fields which avoids the inefficiencies and inadequacies of conventional schemes, including block based approaches.
In one embodiment, the apparatus and method for interlaced motion image compression provides predicted image frames having a reference field and an error field from the interlaced motion image frames. The reference field can be one of the first and second fields in the interlaced frame. Thus, the reference field has the same values as, for example, the first field. The reference field provides the still image content of the frame, preferably on a value by value basis.
The error field provides the motion image content of the frame on a value by value basis. Specifically, for the values corresponding to each location in the prediction field, the error field provides a value corresponding to the motion between fields. The error field can be obtained by first obtaining a prediction field that provides what the non-reference field (e.g., the second field) would be if there were no motion between the first and second fields. Then the error field is determined using the difference between the second field and the prediction field.
The first and second fields are easily recovered from the predicted frame data. One of the fields (e.g., the first) is determined to be the reference field, which is part of the predicted image frames. The remaining field is obtained by summing the prediction and error fields, thus reversing the forward interlaced image processing steps.
In image processing, still content in a frame can be efficiently encoded, as it is highly correlated. The interlaced motion image compression scheme takes advantage of any and all coding efficiency provided by auto-correlation, because the values in the error field corresponding to still portions of the frame will be small. This is in marked contrast to the block based approach, which can often predict a block having substantial still portions to be a motion block and thus lose the coding benefit of the still portions.
The apparatus and method for interlaced image processing also solves various other problems present with conventional schemes. For example, the image is processed as a continuous function, and so avoids discontinuous artifacts, and alleviates problems related to motion between fields, since the reference field provides the still content for both fields, and the error field provides the relative motion between the fields.
Another embodiment of the apparatus and method for interlaced motion image compression receives frames having geometrically interlaced first and second fields and uses a vertical transform to produce frames having high and low frequency fields that each correspond to the first and second fields. Vertical transformation according to this embodiment groups lines together in time to provide good motion correlation. Additionally, the auto-correlation in the frame from still portions is taken advantage of through the reduced magnitude of high band components.
In further embodiments, wavelet transform techniques are used to process interlaced motion images, including by implementing vertical transformations using wavelet transforms. Particular wavelet embodiments use two-dimensional, nonseparable, wavelet techniques, including near orthogonal, odd-sized filter systems. Other particular wavelet embodiments use two-dimensional, biorthogonal filters; and spatial-only wavelet transforms. Embodiments are particularly useful for processing images that are a mixture of interlaced and progressive (noninterlaced) video.
The present invention has other advantages and features which will be more readily apparent from the following detailed description of the invention, in conjunction with the accompanying drawings.
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Bromberg & Sunstein LLP
Johnson Timothy M.
QuVIS, Inc.
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