Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-03-13
2001-07-03
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240010
Reexamination Certificate
active
06256350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to image processing and more specifically pertains to a video compression algorithm for increasing the data throughput on a limited bandwidth link between a host and a digital video camera.
2. Description of Related Art
A digital image represents a two-dimensional array of samples, where each sample is called a pixel. Precision determines how many levels of intensity can be represented and is expressed as the number of bits/sample. Resolution of an image refers to its capability to reproduce fine details. Higher resolution requires more complex imaging systems to represent these images in real-time. In video systems, resolution refers to the number of line pairs resolved on the face of the display screen, expressed in cycles per picture height, or cycles per picture width. Full motion video is characterized with at least 24-Hz frames/sec, and 30 or even 60 frames/sec for high definition TV. For animation, acceptable frame rate is in the range of 15-19 frames/sec while for video telephony it is 5-10 frames/sec. Videoconferencing and interactive multimedia applications require the rate of 15-30 frames/sec.
Commercial imaging applications are surfacing in digital broadcast television, compact disk video, multimedia, video teleconferencing systems, dynamic medical imaging devices, and high definition TV. Imaging applications are time critical and computationally and data intensive, and require both the storage and transmission of enormous data sets which can be accomplished with image compression. Achieving the compression ratios necessary for digital video involves the processing of individual images to remove spatial redundancies and a motion analysis of the sequence to remove temporal redundancies.
The latest models of still and video cameras are solid-state cameras which use silicon chips for image data arrays. Since the size of the camera and the chip should be kept small, these cameras have to keep low the number of sampled image data transferred from the camera to an accompanying host image processing device. Furthermore, the mass consumers of the digital video cameras are used to viewing video images on TV at the frame rate of 30 frames per second. The currently available buses between digital video cameras and the host system have a limited bandwidth of less than 8 frames per second, which limits the number of video frames that can be transferred from the camera to the host and provides fuzzy pictures. These buses do not allow real-time video data transmission.
In order to attract the average user to purchase a digital camera, the throughput of data through a low bandwidth transmission channel between the camera and the host has to be improved by compression. The real time image processing presently involves at least three types of tradeoffs: performance versus image resolution, performance versus storage size, and performance versus input and output bandwidth. The quality of performance is influenced by the cost. Expensive compression schemes, such as MPEG, are not cost effective for low cost single chip cameras. The basic measure for the performance of a compression algorithm is compression ratio, defined as a ratio of original data size and compressed data size. There is a trade-off between the compression ratio and the picture quality. Higher compression ratios may produce lower picture quality. Quality of compression can also vary according to source image characteristics and scene content.
Therefore, there is a need for a low cost method which can improve the data bandwidth between the digital video camera and the host by applying video compression to the digital video stream before the video frame is transmitted to the host computer, which is capable of generating sharp, high quality color images in real time. Furthermore, there is a need for small and inexpensive digital solid-state video cameras capable of transferring 30 video frames per second. These cameras have to have a low gate count and low power requirements so that the size and cost of the camera is minimal.
OBJECTS AND SUMMARY OF THE INVENTION
It is a primary object of the present invention to overcome the aforementioned shortcomings associated with the prior art and to provide an image processing device which uses a low cost video compression method which is capable of generating sharp, high quality color images in real time.
Another object of the present invention is to provide a compression method which performs separate compression in the Y domain and the Cr/Cb domain.
Yet another object of the present invention is to provide a compression method with minimum computational complexity which can be implemented in hardware.
Still another object of the present invention is to provide small and inexpensive digital solid-state video cameras capable of transferring more than 20 video frames per second, which have a low gate count and low power requirements.
These as well as additional objects and advantages of the present invention are achieved by a video compression method that performs separate luminance (Y) domain compression of the video data on a line-by-line basis, without storing video data lines or video data frames, and separate chrominance (Cr/Cb) domain averaging of the video data on a region-by-region basis without storing video data in video frames. The Y and Cr/Cb domain compression steps are implemented in the digital solid-state imaging device hardware for real time link transmission of the compressed video data to the host computer.
The method of the present invention is implemented in a pixel processing controller of the digital imaging device, such as a solid-state camera, working in isochronous traffic mode in the YCbCr 4:2:0 or 4:2:2 format, and adapted for a bandwidth-limited bus with isochronous pipes, one transmitting the Y domain values and another transmitting the Cr/Cb domain values. The Y domain compression module is adapted to determine pixels in the video line which are tagged on a pixel-by-pixel basis, according to differences in the pixel luminance values, and lengths between the tagged pixels. The Cr/Cb domain compression module is adapted to calculate a single average value for a plurality of Cr locations, and a single average value for a plurality of Cb locations.
In one embodiment of the present invention the Cr/Cb domain compression module obtains a single Cr value for each four Cr values, and a single Cb value for each sixteen Cb values in the 4:2:0 format, or a single Cr value for each eight Cr values, and a single Cb value for each thirty-two Cb values in the 4:2:2 format. In another embodiment of the present invention the compressed data is encoded and codes concatenated separately in the Y domain and in the Cr/Cb domain, before the transmission to the host computer. The concatenation in the Cr/Cb domain produces alternative Cr-only lines and Cr/Cb lines, where each Cr-only line has only Cr values, and each Cr/Cb line has alternating Cr and Cb values.
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Bishay Magued M.
Katibian Behnam S.
Akin Gump Strauss Hauer & Fled, L.L.P.
Conexant Systems Inc.
Kelley Chris
Rourk Christopher J.
Wong Allen
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