Image analysis – Image transformation or preprocessing – Changing the image coordinates
Reexamination Certificate
2001-03-21
2004-10-26
Patel, Kanji (Department: 2625)
Image analysis
Image transformation or preprocessing
Changing the image coordinates
C382S233000, C382S268000
Reexamination Certificate
active
06810154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to high efficiency compression encoding and decoding methods for video data of moving images, and particularly to a methods and an apparatus for automatic switching of spatial resolution of video signals to be encoded in accordance with properties of images during encoding of the moving images.
2. Description of the Related Art
Image compression is performed to transmit a maximum quality of images within a limited bandwidth in moving image transmissions. The image compression for a given spatial resolution, such compression methods as MPEG-4 and H.263 are employed, for example. In such compression methods for the moving images, there are requirements to switch the spatial resolution in encoding in accordance with complexity of the images in a same scene and in a same bit stream.
FIG. 1
shows a conventional switching apparatus for switching the spatial resolution. In
FIG. 1
, a switching apparatus
100
includes an encoding unit
101
, a single frame averaged quantization size calculation unit
102
, an originated data bit counter unit
103
, a resolution decision unit
104
and a memory unit
105
. A moving image signal
110
with a certain resolution is input to the encoding unit
101
. At first, a switching of the resolution takes place in accordance with a resolution
111
that is determined by the resolution decision unit
104
. Then, the encoding unit
101
encodes the moving images into a bit stream
112
by a given compression method, and also the encoding unit
101
outputs a quantization size
113
for each of blocks, which is input to the single frame averaged quantization size calculation unit
102
. The resolution decision unit
104
determines a resolution
111
by threshold values QP
1
, QP
2
, FR
1
and FR
2
as will be described later, based on an originated data bit quantity
114
(the number of information bits) from the originated bit counter unit
103
, a quantization size
115
output by the single frame averaged quantization size calculation unit
102
, and a previous resolution
116
output by the memory
105
.
An example of conventional technology for the resolution decision unit
104
may be referred to ITU-T Document Q15-C-15 “Video Codec Test Model, Near-Term, Version 9” issued in December 1997.
FIG. 2
shows a process flow of the resolution decision method disclosed in this document. This method is based on a principle that a product of an average quantization size (QPpre in
FIG. 2
) expresses a complexity, i.e., a degree of difficulty in encoding, and an originated data size (B in FIG.
2
).
FIG. 2
represents operations for one frame. In a step
201
, necessary parameters are provided. Th
1
and Th
2
represent threshold values. QPpre represents a single frame averaged quantization size of a frame encoded most recently. B represents an originated data volume of the frame that was encoded most recently. QP
1
, QP
2
, FR
1
and FR
2
are parameters to determine the threshold values. TB represents a targeted bit rate. Here, the threshold value Th
1
is a threshold value with respect to image complexity in a high spatial resolution. If a product of the single frame averaged quantization size QPpre for the most recent encoded frame, as described in above, and the originated data volume B of the most recent encoded frame is larger than the threshold value Th
1
, then it is determined that the image is exceedingly complex, and the resolution for the image to be encoded is chosen to be low. Conversely, the threshold value Th
2
is a threshold value with respect to the image complexity in a low spatial resolution. If the product of the single frame averaged quantization size QPpre for the most recent encoded frame, as described in above, and the originated data volume B is smaller than the threshold value Th
2
, then it is determined that the image is not complex, and the resolution for the image to be encoded is chosen to be high. FR
1
is a frame rate corresponding to the high resolution, and FR
2
is a frame rate corresponding to the low resolution. FR
1
and FR
2
may be equal.
In a step
202
, the threshold values Th
1
and Th
2
are determined. The threshold value Th
1
is calculated by multiplying the parameter QP
1
to the target bit rate per frame TB/FR
1
for the high resolution. Similarly, the threshold value Th
2
is calculated by multiplying the parameter QP
2
to the target bit rate per frame TB/FR
2
for the low resolution.
In a step
203
, a present spatial resolution, whether high or low, is checked. If the present spatial resolution is high, then the process proceeds to a step
204
, otherwise it proceeds to a step
205
.
In a step
204
, a decision is made whether or not the resolution for the next frame should be lowered, given that the present spatial resolution is high. Actually, the threshold value Th
1
is compared with the product of the single frame averaged quantization size QPpre for the most recently encoded frame and the originated data volume B for the most recently encoded frame, and if the product of QPpre and B is larger than Th
1
, then the spatial resolution for the next frame is lowered in a step
206
.
In a step
205
, a decision is made whether or not the resolution for the next frame should be heightened, given that the present spatial resolution is low. Actually, the threshold value Th
2
is compared with the product of the single frame averaged quantization size QPpre for the most recently encoded frame and the originated data volume B for the most recently encoded frame, and if the product of QPpre and B is lower than Th
2
, then the spatial resolution for the next frame is heightened in a step
207
.
In conventional technologies as described above, there is a problem. If a video content is of relatively still with modest movement, that is, if there is no discontinuity, such as scene changes, or abrupt movements in the contents, the product of the single frame averaged quantization size QPpre of the most recent encoded frame and the originated data volume B for the most recently encoded frame may be used as a standard to express the complexity of images. However, where the contents include images with such discontinuity as scene changes and abrupt movements, the product cannot be used as the standard for the image complexity. However, the product has been used as the standard to express the image complexity in conventional technologies.
For this reason, as described above, parameters have had to be manually adjusted in encoding when a video program contains images with abrupt motions, while the motions may not be highly visible to an audience, which has made a realtime encoding impossible and required a certain expertise to set the parameters.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a method and an apparatus that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art.
Another object of the present invention to provide a method and an apparatus that automatically switches the spatial resolution of an image to be encoded by properties of the image, even during the encoding process.
The above objects of the present invention are achieved by an automatic setting method of a spatial resolution for a moving image, comprising the steps of: dividing the moving image into blocks and compression encoding the moving image for each of the blocks; decoding an encoded moving image thus obtained; obtaining a block distortion ratio from a decoded image; and making a resolution decision to select a first resolution lower than a current spatial resolution if the block distortion ratio is greater than a first threshold value or a second resolution higher than the current spatial resolution if the block distortion ratio is smaller than a second threshold value. In this manner, block distortions generated by a larger quantization size that has been introduced to compress the data volume to the required bit rate are suppressed.
The above
Fujitsu Limited
Patel Kanji
Staas & Halsey , LLP
LandOfFree
Method and apparatus for automatic spatial resolution... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for automatic spatial resolution..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for automatic spatial resolution... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3291282