Image analysis – Image compression or coding – Transform coding
Reexamination Certificate
2000-12-18
2004-02-10
Boudreau, Leo (Department: 2621)
Image analysis
Image compression or coding
Transform coding
C382S299000, C375S240210
Reexamination Certificate
active
06690836
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to image processing circuits and techniques, and more particularly to a circuit and method for decoding an encoded version of an image having a resolution directly into a decoded version of the image having another resolution. For example, such a circuit can down-convert an encoded high-resolution (hereinafter “hi-res”) version of an image directly into a decoded low-resolution (hereinafter “lo-res”) version of the image without an intermediate step of generating a decoded hi-res version of the image.
BACKGROUND OF THE INVENTION
It is sometimes desirable to change the resolution of an electronic image. For example, an electronic display device such as a television set or a computer monitor has a maximum display resolution. Therefore, if an image has a higher resolution than the device's maximum display resolution, then one may wish to down-convert the image to a resolution that is lower than or equal to the maximum display resolution. For clarity, this is described hereinafter as down-converting a hi-res version of an image to a lo-res version of the same image.
FIG. 1
is a pixel diagram of a hi-res version
10
of an image and a lo-res version
12
of the same image. The hi-res version
10
is n pixels wide by t pixels high and thus has n×t pixels P
0,0
-P
t,n
. But if a display device (not shown) has a maximum display resolution of [n×g] pixels wide by [t×h] pixels high where g and h are less than one, then, for display purposes, one typically converts the hi-res version
10
into the lo-res version
12
, which has a resolution that is less than or equal to the maximum display resolution. Therefore, to display the image on the display device with the highest possible resolution, the lo-res version
12
has (n×g)×(t×h) pixels P
0,0
-P
(t×h),(n×g)
. For example, suppose that the hi-res version
10
is n=1920 pixels wide by t=1088 pixels high. Furthermore, assume that the display device has a maximum resolution of n×g=720 pixels wide by t×h=544 pixels high. Therefore, the lo-res version
12
has a maximum horizontal resolution that is g=⅜ of the horizontal resolution of the hi-res version
10
and has a vertical resolution that is h=½ of the vertical resolution of the hi-res version
10
.
Referring to
FIG. 2
, many versions of images such as the version
10
of
FIG. 1
are encoded using a conventional block-based compression scheme before they are transmitted or stored. Therefore, for these image versions, the resolution reduction discussed above in conjunction with
FIG. 1
is often carried out on a block-by-block basis. Specifically,
FIG. 2
illustrates the down-converting example discussed above in conjunction with
FIG. 1
on a block level for g=⅜ and h=½. An image block
14
of the hi-res version
10
(
FIG. 1
) is 8 pixels wide by 8 pixels high, and an image block
16
of the lo-res version
12
(
FIG. 1
) is 8×⅜=3 pixels wide by 8×½=4 pixels high. The pixels in the block
16
are often called sub-sampled pixels and are evenly spaced apart inside the block
16
and across the boundaries of adjacent blocks (not shown) of the lo-res version
12
. For example, referring to the block
16
, the sub-sampled pixel P
0,2
is the same distance from P
0,1
as it is from the pixel P
0,0
in the block (not shown) immediately to the right of the block
16
. Likewise, P
3,0
is the same distance from P
2,0
as it is from the pixel P
0,0
in the block (not shown) immediately to the bottom of the block
16
.
Unfortunately, because the algorithms for decoding an encoded hi-res version of an image into a decoded lo-res version of the image are inefficient, an image processing circuit that executes these algorithms often requires a relatively high-powered processor and a large memory and is thus often relatively expensive.
For example, U.S. Pat. No. 5,262,854 describes an algorithm that decodes the encoded hi-res version of the image at its full resolution and then down-converts the decoded hi-res version into the decoded lo-res version. Therefore, because only the decoded lo-res version will be displayed, generating the decoded hi-res version of the image is an unnecessary and wasteful step.
Furthermore, for encoded video images that are decoded and down converted as discussed above, the motion-compensation algorithms are often inefficient, and this inefficiency further increases the processing power and memory requirements, and thus the cost, of the image processing circuit. For example, U.S. Pat. No. 5,262,854 describes the following technique. First, a lo-res version of a reference frame is conventionally generated from a hi-res version of the reference frame and is stored in a reference-frame buffer. Next, an encoded hi-res version of a motion-compensated frame having a motion vector that points to a macro block of the reference frame is decoded at its full resolution. But the motion vector, which was generated with respect to the hi-res version of the reference frame, is incompatible with the lo-res version of the reference frame. Therefore, a processing circuit up-converts the pointed-to macro block of the lo-res version of the reference frame into a hi-res macro block that is compatible with the motion vector. The processing circuit uses interpolation to perform this up conversion. Next, the processing circuit combines the residuals and the hi-res reference macro block to generate the decoded macro block of the motion-compensated frame. Then, after the entire motion-compensated frame has been decoded into a decoded hi-res version of the motion-compensated frame, the processing circuit down-converts the decoded hi-res version into a decoded lo-res version. Therefore, because reference macro blocks are down-converted for storage and display and then up-converted for motion compensation, this technique is very inefficient.
Unfortunately, the image processing circuits that execute the above-described down-conversion and motion-compensation techniques may be too expensive for many consumer applications. For example, with the advent of high-definition television (HDTV), it is estimated that many consumers cannot afford to replace their standard television sets with HDTV receiver/displays. Therefore, a large consumer market is anticipated for HDTV decoders that down-convert HDTV video frames to standard-resolution video frames for display on standard television sets. But if these decoders incorporate the relatively expensive image processing circuits described above, then many consumers that cannot afford a HDTV receiver may also be unable to afford a HDTV decoder.
Overview of Conventional Image-Compression Techniques
To help the reader more easily understand the concepts discussed above and discussed below in the description of the invention, following is a basic overview of conventional image-compression techniques.
To electronically transmit a relatively high-resolution image over a relatively low-band-width channel, or to electronically store such an image in a relatively small memory space, it is often necessary to compress the digital data that represents the image. Such image compression typically involves reducing the number of data bits necessary to represent an image. For example, High-Definition-Television (HDTV) video images are compressed to allow their transmission over existing television channels. Without compression, HDTV video images would require transmission channels having bandwidths much greater than the bandwidths of existing television channels. Furthermore, to reduce data traffic and transmission time to acceptable levels, an image may be compressed before being sent over the internet. Or, to increase the image-storage capacity of a CD-ROM or server, an image may be compressed before being stored thereon.
Referring to
FIGS. 3A-9
, the basics of the popular block-based Moving Pictures Experts Group (MPEG) co
Campbell T. George
Natarajan Ramachandran
Boudreau Leo
Equator Technologies Inc.
Graybeal Jackson Haley LLP
Sherali Ishrat
LandOfFree
Circuit and method for decoding an encoded version of an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit and method for decoding an encoded version of an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit and method for decoding an encoded version of an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3331080