Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-05-17
2003-11-11
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240120, C375S240130, C375S240150
Reexamination Certificate
active
06647060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video compression device compressing video images, and more particularly to a video compression device and a video compression method allowing video data to be transmitted at an optimum frame rate in accordance with the input frame rate of original images, such as MPEG1-compressed video, and a user-specified compression level.
2. Description of the Related Art
Digitized images recorded on recording media, such as CD-ROM discs or hard disks, are usually compressed because they take up a huge amount of space. There are many compression methods. In many cases, the DCT-based coding method is used. It takes advantage of the characteristics that the spatial frequencies of an image concentrate on low frequencies. This coding method is adopted as the international standard coding methods such as JPEG (Joint Photographic Expert Group) or MPEG (Moving Pictures Expert Group) 1 and 2.
These storage types of video compression methods, such as MPEG1, use a predetermined number of frames per unit time. Therefore, when the frame rate of the input image is lower than that of MPEG1, the same frame must be inserted more than once. This generates redundant frames, thus decreasing compression efficiency. On the other hand, the international standard MPEG1 coding method cannot increase the compression rate by reducing the frame rate.
The “video signal coding method and video signal coding unit”, disclosed in Japanese Patent Laid-Open Application No. Hei 10-42295, is designed to reduce the amount of redundant frames. To reduce the coding amount of frames, the unit and method disclosed in this publication generate a code indicating that a frame generated during inter-frame compression is a copy of some other frame, as shown in FIG.
9
.
That is, to reduce the virtual frame rate while satisfy the frame rate defined by MPEG, the unit described in the above publication has a copy stream generator
49
generating a copy-word bit stream (copy system) indicating that a picture is the same as another already-copied picture. A system controller
45
does not perform movement compensation for B pictures or P pictures to be deleted; instead, the system controller
45
supplies a code-word bit stream (copy stream)
49
a
, output from the copy stream generator
49
, to a buffer
37
via an output data switching switch
46
which constitutes a code multiplexer. Periodically inserting the code-word bit stream created by simply copying the preceding or following frame makes a frame rate lower than the normal frame rate.
On the other hand; the “video image coding unit”, disclosed in Japanese Patent Publication (unexamined) No. A-9-130787, controls a switch
101
, as instructed by a control signal from the coding control circuit for frame processing, as shown in FIG.
10
. This unit selects frames to be skipped according to the actual amount of coding to adjust the frame rate.
That is, to implement a coding frame rate in accordance with the picture quality and to cause a little delay, the unit disclosed in this publication comprises a coding unit
117
which codes input video signals, an output buffer
115
which receives data coded by the coding unit
117
and outputs the coded data at a predetermined rate, and a coding control circuit
116
which selects frames to be coded. The coding control circuit
116
calculates the target amount of coding for each frame based on the externally-set coding bit rate, coding frame rate, and allowable delay time. It them compares the calculated value with the actual value, controls a quantization circuit
106
and the switch
101
, and adjusts the quantization parameters and the number of frames to be skipped.
However, on the “video signal coding method and video signal coding unit” disclosed in Japanese Patent Publication (unexamined) No. A-10-42295, the frequency at which code indicating that a frame is a copy of some other frame is generated does not always match the input frame rate or the user-desired virtual output frame rate. This means that processing all input image data decreases efficiency.
On the “video image coding unit” disclosed in Japanese Patent Publication (unexamined) A-9-130787, the frame rate depends on the amount of coding, preventing some images from moving smoothly.
SUMMARY OF THE INVENTION
The present invention seeks to solve the problems associated with prior arts described in the above publications. It is an object of the present invention to provide a video compression device and a video compression method which provide efficiently-compressed and smoothly-moving video.
When the frame rate of the input image differs from a desired frame rate on a compressed video storage device, the present invention enables the user to generate the optimum frame configuration so that video may be compressed efficiently and to delete or insert frames according to the configuration while using as much input frames as possible.
The present invention provides a video compression device compressing video signals, comprising:
a frame receiving unit receiving the video signals, one frame at a time;
a frame checking unit checking a type of the frame to be processed and passing control to an appropriate unit;
a motion search unit searching a small block for a motion of an image;
a frequency conversion unit converting the image of the small block to a spatial frequency;
a quantization unit performing quantization for the image signals frequency-converted by the frequency conversion unit;
a reverse quantization unit performing reverse quantization for the signals output from the quantization unit;
a reverse frequency conversion unit performing reverse frequency conversion for the signals output from the reverse quantization unit;
a motion compensation unit compensating a motion of the image of the small block and generating an original image; and
a variable-length coding unit performing variable-length coding for the signals output from the quantization unit and outputting the signals to a compressed code output unit.
In addition, the present invention provides a video compression method of compressing video signals, the method being processed by a frame receiving unit receiving the video signals, one frame at a time; a frame checking unit checking a type of the frame to be processed and passing control to an appropriate unit; a motion search unit searching a small block for a motion of an image; a frequency conversion unit converting the image of the small block to a spatial frequency; a quantization unit performing quantization for the image signals frequency-converted by the frequency conversion unit; a reverse quantization unit performing reverse quantization for the signals output from the quantization unit; a reverse frequency conversion unit performing reverse frequency conversion for the signals output from the reverse quantization unit; a motion compensation unit compensating a motion of the image of the small block and generating an original image; and a variable-length coding unit performing variable-length coding for the signals output from the quantization unit and outputting the signals to a compressed code output unit, the method comprising the steps of:
identifying the type of the frame by the frame checking unit that the frame is an I frame, P frame, or B frame;
passing control to the frequency conversion unit if the frame is the I frame;
passing control to the motion search unit if the frame is the P frame; and
passing control directly to the compressed code output unit if the frame is the B frame.
The present invention also provides a video compression method according to the above-described method, further comprising the steps of:
getting a frame rate of the input video image;
getting a user-specified compression level;
if the input frame rate is smaller than a predetermined maximum output frame rate, changing the predetermined maximum output frame rate to the input frame rate;
calculating an effective frame rate according to:
formula: (Level−1)×(Max−Min)
Le Vu
NEC Corporation
Whitham Curtis & Christofferson, P.C.
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