1. Field of Invention
The present invention relates to digital video decompression, de-interlacing and frame rate conversion. And, more specifically to an efficient video bit stream decompression, de-interlacing and constructing new image directly from video decompression procedure which sharply reduces the 10 bandwidth requirement of the frame buffer.
2. Description of Related Art
ISO and ITU have separately or jointly developed and defined some digital video compression standards including MPEG-1, MPEG-2, MPEG-4, MPEG-7, H.261, H.263 and H.264. The success of development of the video compression standards fuels wide applications which include video telephony, surveillance system, DVD, and digital TV. The advantage of digital image and video compression techniques significantly saves the storage space and transmission time without sacrificing much of the image quality.
Most ISO and ITU motion video compression standards adopt Y, U/Cb and V/Cr as the pixel elements, which are derived from the original R (Red), G (Green), and B (Blue) color components. The Y stands for the degree of “Luminance”, while the Cb and Cr represent the color difference been separated from the “Luminance”. In both still and motion picture compression algorithms, the 8×8 pixels “Block” based Y, Cb and Cr goes through the similar compression procedure individually.
There are essentially three types of picture encoding in the MPEG video compression standard. I-frame, the “Intra-coded” picture uses the block of 8×8 pixels within the frame to code itself. P-frame, the “Predictive” frame uses previous I-type or P-type frame as a reference to code the difference. B-frame, the “Bi-directional” interpolated frame uses previous I-frame or P-frame as well as the next I-frame or P-frame as references to code the pixel information. In principle, in the I-frame encoding, all “Block” with 8×8 pixels go through the same compression procedure that is similar to JPEG, the still image compression algorithm including the DCT, quantization and a VLC, the variable length encoding. While, the P-frame and B-frame have to code the difference between a target frame and the reference frames.
In compressing or decompressing the P-type or B-type of video frame or block of pixels, the referencing memory dominates high semiconductor die area and cost. If the referencing frame is stored in an off-chip memory, due to I/O data pad limitation of most semiconductor memories, accessing the memory and transferring the pixels stored in the memory becomes bottleneck of most implementations. One prior method overcoming the I/O bandwidth problem is to use multiple chips of memory to store the referencing frame which cost linearly goes higher with the amount of memory chip. Some times, higher speed clock rate of data transfer solves the bottleneck of the I/O bandwidth at the cost of higher since the memory with higher accessing speed charges more and more EMI problems in system board design. In MPEG2 TV application, a Frame of video is divided to be “odd field” and “even field” with each field being compressed separately which causes discrepancy and quality degradation in image when 2 fields are combined into a frame before display.
De-interlacing is a method applied to overcome the image quality degradation before display. For efficiency and performance, 3-4 of previous frames and future frames of image are used to be reference for compensating the potential image error caused by separate quantization. De-interlacing requires high memory I/O bandwidth since it accesses 3-5 frames.
In some display applications, frame rate or field rate need to be converted to fit the requirement of higher quality and the frame rate conversion is needed which requires referring to multiple frames of image to interpolate extra frames which consumes high bandwidth of memory bus as well.
The method of this invention of video de-interlacing and frame rate conversion coupled with video decompression and applying referencing frame compression significantly reduces the requirement of memory 10 bandwidth and costs less storage device.
The present invention is related to a method of digital video de-interlacing with the referencing frame buffer compression and decompression which reduces the semiconductor die area/cost sharply in system design. This method sharply reduces the memory I/O bandwidth requirement if off-chip memory is applied to store the compressed referencing frame.
The present invention of this efficient digital video de-interlacing compresses and reduces the data rate of the digital video frames which are used as reference for video de-interlacing.
According to one embodiment of the present invention, the recompressed lines of multiple frames are used to de-interlacing and frame rate conversion by applying interpolation means when the video decoding is in process.
According to one embodiment of the present invention, multiple video decoding engines are running in parallel to reconstruct at least two fields/frames at a time and the already reconstructed two referencing frames/fields together with the two under reconstruction can be used to de-interlacing and interpolating to form new frame.
According to one embodiment of the present invention, a predetermined time is set to reconstruct a slice of blocks of Y and UN pixel components video de-interlacing and frame rate conversion by interpolation means.
According to one embodiment of the present invention, at least two lines of pixel buffer is designed to temporarily store a slice of decompressed blocks of Y and Cr/Cb pixel components for video de-interlacing and frame rate conversion.
According to another embodiment of the present invention, the line by line pixels formed by de-interlacing and by interpolating to form new video frame are separately writing into the frame buffer memory.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.
There are essentially three types of picture coding in the MPEG video compression standard as shown in
In most applications, since the I-frame does not use any other frame as reference and hence no need of the motion estimation, the image quality is the best of the three types of pictures, and requires least computing power in encoding since no need for motion estimation. The encoding procedure of the I-frame is similar to that of the JPEG picture. Because of the motion estimation needs to be done in referring both previous and/or next frames, encoding B-type frame consumes most computing power compared to I-frame and P-frame. The lower bit rate of B-frame compared to P-frame and I-frame is contributed by the factors including: the averaging block displacement of a B-frame to either previous or next frame is less than that of the P-frame and the quantization step is larger than that in a P-frame. In most video compression standard including MPEG, a B-type frame is not allowed for reference by other frame of picture, so, error in B-frame will not be propagated to other frames and allowing bigger error in B-frame is more common than in P-frame or I-frame. Encoding of the three MPEG pictures becomes tradeoff among performance, bit rate and image quality, the resulting ranking of the three factors of the three types of picture encoding are shown as below:
In some video applications like TV set, since the display frequency is higher than 60 frames per second (60 fps), most likely, interlacing mode is adopted, in which, as shown in
Another procedure consuming a lot memory 10 bandwidth is the frame rate conversion which interpolates and forms new frame between decoded frames. For a video with 30 frames per second or said 30 fps converting to 60 fps, or from a 60 fps converting to 120 fps, the easiest way is to repeat very frame which can not gain good image quality. As shown in
The present invention provides method of reducing the required bandwidth by buffering the decompressed lines of video image and applying these reconstructed lines of pixels to function as de-interlacing and interpolating to form the needed new frame of pixels and these two function of de-interlacing and frame rate conversion (or frame interpolation) are done by referring to those pixels temporarily stored in the line buffers. Therefore it avoids the need of multiple accessing the same referencing frame buffer.
To achieve higher image quality, 3-4 previous frames/fields and 3-4 previous frames/fields might be referred for de-interlacing, and/or for interpolation to construct new frame in frame rate conversion which consume much more 10 bandwidth. By applying this present invention, the pixels accessed from the referencing frame for video decompression and the reconstructed pixels are stored in the on-chip line buffer used for de-interlacing and frame rate conversion to form new frame without accessing multiple times of the referencing frame of pixels.
Applying this invention, the decompressed rows of macro-block video frame of pixels stored in the on-chip line buffer can be referred for future field/frame decompression and de-interlacing as well as frame rate conversion before written to the frame buffer or other storage device and can avoid multiple accessing for de-interlacing and later for frame rate conversion.
It will be apparent to those skills in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or the spirit of the invention. In the view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.