Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1999-06-16
2002-01-29
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Reexamination Certificate
active
06343097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relats to a recursive noise reducer for reducing a noise of a digital video signal and to a noise reducing method thereof. The present invention also relates to a noise reducer, a noise reducing method, a picture signal processing apparatus, and a motion detecting method suitable for recording/reproducing a picture to/from a record medium such as an optical disc or a magnetic tape and for transmitting a picture from a transmitting side to a receiving side through a transmission path in a television conference system, a television telephone system, a broadcasting unit, and so forth.
2. Description of the Related Art
A recursive noise reducer using a frame memory has been well known in the field of digital picture signal process. The recursive noise reducer obtains the differences between an input video signal and a video signal of one frame prior received from the frame memory, extracts portions having small levels from the differences as noise components, and subtracts the extracted noise components from the input video signal. Thus, the recursive noise reducer reduces the noise of the input video signal and writes the resultant video signal to the frame memory. When a field memory is used instead of the frame memory, the capacitance of the memory can be decreased.
FIG. 1
is a block diagram showing an example of the structure of a conventional noise reducer. An input video signal that has been converted into a digital signal (referred to as input video signal Vin) is received from an input terminal
201
. The input video signal Vin is supplied to subtracting devices
202
and
204
. An output signal of the subtracting device
202
is obtained from an output terminal
207
. In addition, the output signal of the subtracting device
202
is written to a frame memory
205
. A memory controller
206
is disposed corresponding to the frame memory
205
. The memory controller
206
controls a writing operation and a reading operation of the frame memory
205
. The read data of the frame memory
205
is delayed by one frame against the write data. An output signal of the frame memory
205
is denoted by Vout. One frame delay is denoted by F
−1
. Thus, the output signal Vout·F
−1
of the frame memory
205
is supplied to the subtracting device
204
. Since the input picture signal Vin is supplied to the subtracting device
204
, the subtracting device
204
generates a frame difference.
The output signal of the subtracting device
204
is supplied to the subtracting device
202
through a non-linear circuit
203
. The non-linear circuit
203
multiplies the output signal of the subtracting device
204
by feed-back coefficient K corresponding to the level of the input picture signal. The non-linear circuit
203
is composed of a ROM. As input/output characteristics of the non-linear circuit
203
, when the level of the input signal (frame difference) is small, feed-back coefficient K=1 is set and the input signal is output as a noise component. When the level of the input signal is intermediate, the level of the output signal is limited to a predetermined value. When the level of the input signal is large, the output signal is decreased. When the level of the input signal is much large, assuming that a frame difference takes place due to a motion, the level of the output signal is 0.
Thus, using the characteristics of which the inter-frame correlation and the amplitude of a noise component are small, the non-linear circuit
203
extracts the noise component. The subtracting device
202
subtracts the extracted noise component from the input video signal. Thus, the noise can be reduced.
The output video signal Vout can be expressed by the following formula.
V
out=
V
in−
K·
(
V
in−
V
out·
F
−1
)=
V
in·(1
−K
)/(1−
K·F
−1
) (1)
In the above-described noise reducer, when there is a moving portion on a picture, the inter-frame correlation is lost. Thus, since it becomes difficult to distinguish a noise from an input signal, a moving blur takes place. To solve such a problem, a noise reducer (for example, Japanese Patent Laid-Open Publication No. 7-15630) has been proposed. In the noise reducer, an inter-frame or inter-field moving vector in a particular direction of the entire picture is detected. The delay amount of the memory is controlled corresponding to the amount of movement.
In addition, a method for improving the prediction accuracy of the motion compensation of an encoder (for example, Japanese Patent Laid-Open Publication No. 6-296278) has been proposed. In the method, a pre-processing apparatus of a motion compensation prediction encoding apparatus performs a motion compensation predicting process for an input picture that has a large moving portion and contains many random noise components.
In the noise reducer (Japanese Patent Laid-Open Publication No. 7-15630), which performs the motion compensating process, although a moving blur due to a parallel movement of a whole picture can be alleviated, a moving blue due to a plurality of moving portions on a picture cannot be alleviated.
On the other hand, in the method (Japanese Patent Laid-Open Publication No. 6-296276), since the motion compensating process is performed block by block, a block distortion of which the boundary of a block is conspicuous on a decoded picture takes place. In addition, to obtain an inter-frame moving vector, a frame memory is required. Thus, the cost of the apparatus increases.
OBJECTS AND SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a noise reducer, a noise reducing method, and a picture signal processing apparatus for suppressing a moving blur without a block distortion even if a plurality of moving portions take place on a picture.
Another object of the present invention is to provide a noise reducer, a noise reducing method, and a picture processing apparatus for dividing an interfield difference or an inter-frame difference into a plurality of frequency components so as to properly reduce noise.
A further object of the present invention is to provide a motion detecting method for detecting an inter-field motion or an inter-frame motion for each of a plurality of moving portions.
A first aspect of the present invention is a noise reducer, comprising a moving vector detecting means for dividing a picture signal into a plurality of blocks and detecting moving vectors of the blocks between adjacent fields or adjacent frames, a motion compensating means for extracting a moving portion of a picture of one field prior or one frame prior corresponding to the moving vectors and compensating the motion of the extracted moving portion corresponding to the moving vectors, a difference signal obtaining means for obtaining a difference signal between the picture signal and a signal that has been motion-compensated of one field prior or one frame prior, a non-linear process means for performing a non-linear process for the difference signal, and a combining means for combining the picture signal and the signal that has been non-linear-processed.
A second aspect of the present invention is a noise reducer, comprising a moving vector detecting means for dividing a picture signal into a plurality of blocks and detecting moving vectors of the blocks between adjacent fields or adjacent frames, a motion compensating means for compensating the motion of a picture of one frame prior or one field prior with the moving vectors, a difference signal obtaining means for obtaining a difference signal between the picture signal and a signal that has been motion-compensated of one field prior or one frame prior, a dividing means for dividing the difference signal into a plurality of frequency component difference signals, a non-linear process means for performing a non-linear process for the individual frequency component difference signals, and a combining means for combining the picture signal and the frequency component signals that
Akiba Toshiya
Kobayashi Hiroshi
Takahashi Takao
Tomita Masami
Frommer William S.
Kelley Chris
Kessler Gordon
Sony Corporation
Wong Allen
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