Image analysis – Image compression or coding
Reexamination Certificate
1999-01-26
2003-04-29
Mehta, Bhavesh (Department: 2625)
Image analysis
Image compression or coding
C382S233000, C358S426100
Reexamination Certificate
active
06556714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal processing apparatus and method in which a bit stream supplied as an input is decoded to an image signal and the image signal is provided as a bit stream again.
2. Description of Related Art
For video signal compression, MPEG (moving picture coding experts group) and MPEG-2 have been used more widely in combination with a redundancy reduction by an orthogonal transform such as motion compensation (MC), discrete cosine transform (DCT) or the like.
An audio data not compressed is compressed according to such an MPEG to be a coded image such as an intra-picture coded image (I picture), forward -predictive coded image (P picture) or bi-directional predictive coded image (B picture) for storage into a cumulative recording medium such as magneto-optic disc or the like or for transmission over a communications network.
In this MPEG technique, a bit stream is decoded to be a picture signal which will be transformed into a bit stream again. For transform from a movie film to a video film, four frames are subjected to a so-called 2:3 pulldown processing to produce five frames in order to transform 24 frames/sec on the movie film to 30 frames/sec on a TV/video film.
FIG. 1
illustrates, in a schematic block form, a conventional signal processor in which a bit stream of a moving picture is decoded and the decoded moving picture is coded according to the MPEG-2 Video Compression Standard to output the bit stream.
As shown, the conventional signal processor includes a decoder
101
to decode an external input bit stream S
26
to a picture signal, a post-processing circuit
102
to post-process the decoded picture signal, a pre-processing circuit
103
to pre-process the picture signal for coding, and an encoder
104
to code the picture signal from the pre-processing circuit
103
.
The decoder
101
decodes the input bit stream S
26
to provide a decoded picture S
20
. The decoder
101
also decodes a display control parameter S
23
from the input bit stream S
26
and supplies it to the post-processing circuit
102
. The display control parameter S
23
prescribed in the MPEG-2 Video Compression Standard is horizontal size, vertical_size, frame rate, display_horizontal_size, display_vertical_size, aspect_ratio_information, progressive_frame, repeat_first_field, top_field_first, frame_centre_horizontal_offset, frame_centre_vertical_offset.
The post-processing circuit
102
processes the decoded picture S
20
based on the display control parameter S
23
to provide a post-processed image S
21
. More particularly, the post-processing circuit
102
effects 2:3 pulldown based on top_field_first, repeat_first_field, upsampling of chroma signal from 4:2:0 format to 4:2:2 format based on progressive_frame, and also clipping of a rectangular window from an image and switching to sampling in a display frame size, namely, upsampling or downsampling, based on horizontal_size, vertical_size, display_horizontal_size, display_vertical_size, aspect_ratio_information, frame_centre_horizontal_offset, frame_centre_vertical_offset.
The 4:2:0 format is a component format for coding of video signal, adopted in MP@ML (main profile/main level) of MPEG-2. The
FIGS. 4
,
2
and 0 indicate a sampling frequency ratio, that is, resolution ratio, between a brightness (Y) signal included in the horizontal line (scanning line) of a video signal and two chrominance signals (Cb and Cr). The figures in the 4:2:2 format also indicate such ratios.
The post-processed image S
21
is supplied to the pre-processing circuit
103
in which the post-processed image S
21
is subjected to inverse 3:2 pulldown, downsampling of chroma signal from the 4:2:2 format to 4:2:0 format, etc. to provide a pre-processed signal S
22
. Also the pre-processing circuit
103
provides a display control parameter S
24
indicative of the content of the inverse processing from the pre-processed image S
22
to post-processed image S
21
.
The encoder
104
codes the pre-processed image S
22
and also codes the display control parameter S
24
of the pre-processed image S
22
as a header information of a bit stream of the coded pre-processed image S
22
to provide a bit stream S
27
.
It is well known that for coding an image with a high quality when decoding an MPEG video bit stream and re-coding the decoded image according to MPEG for providing an bit stream, rendering a picture_coding_type being a coding parameter S
25
for coding the image same as that of the original bit stream is effective. For this purpose, the coding parameter S
25
is supplied from the decoder
101
to the encoder
104
. The information carried by the coding parameter S
25
is effected when the decoded image S
20
corresponds one-to-one to the pre-processed image S
22
.
In some cases, however, the coding parameter S
25
cannot effectively be used since the one-to-one correspondence between the decoded image S
20
and pre-processed image S
22
cannot be assured.
As the causes of the decoded image S
20
and pre-processed image S
22
not corresponding one-to-one to each other, the inverse 2:3 pulldown of the post-processed image S
21
by the pre-processing circuit
103
is not any completely inverse one, that the post-processing circuit
102
has switched to sampling in the display frame size, etc.
Also, repeated upsampling of chroma signal in the post-processing circuit
102
and downsampling of chroma signal in the pre-processing circuit
103
will also cause the chroma signal to be deteriorated.
The external bit streams S
26
include ones based on different signal standards. Images S
20
decoded from such external bit streams S
26
in the decoder
101
are different in number of pixels per picture and number of pictures per unit time. For transmission of such images, interfaces meeting the different signal standards have to be used and also hardware and software have to be used which meet such standards.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the above drawbacks of the prior art by providing a signal processing apparatus and method in which coding parameters can be effectively used to code, with a high quality, an image decoded from a bit stream coded from an image signal.
It is another object of the present invention to provide a signal processing apparatus and method, signal decoder and signal encoder in which for transmission of an image decoded from a bit stream coded from an image signal, an existing interface can be used even for images prepared according to different standards and coding parameters can be effectively used to code, with a high quality, an image decoded from a bit stream coded from an image signal.
The above object can be attained by providing a signal processing apparatus comprising, according to the present invention:
means for decoding a bit stream coded from an image signal to provide an image signal and a coding parameter;
a first switching means for selecting a destination to which the image signal from the decoding means is to be sent;
means for post-processing the image signal from a selectable terminal of the first switching means;
means for pre-processing the image signal;
a second switching means for selecting either the image signal from the pre-processing means or the image signal from the first switching means; and
means for coding the image signal from the second switching means and the coding parameter from the decoding means.
The above object can also be attained by providing a signal processing method in which a signal processing apparatus including means for decoding a bit stream coded from an image signal to provide an image signal and a coding parameter; a first switching means for selecting a destination to which the image signal from the decoding means is to be sent; means for post-processing the image signal from a selectable terminal of the first switching means; means for pre-processing the image signal; a second switching means for selecting either the image signal from the pre-processi
Chawan Sheela
Frommer William S.
Frommer & Lawrence & Haug LLP
Mehta Bhavesh
Smid Dennis M.
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