SYSTEMS AND METHODS FOR IMPROVING THE QUALITY OF COMPRESSED VIDEO SIGNALS BY SMOOTHING BLOCK ARTIFACTS
The present invention is directed to systems and methods in which, for a given amount of data required to represent a compressed video signal, the quality of the uncompressed displayed real-time video, as perceived by a typical human viewer, is improved. Systems and methods herein achieve this improvement by attenuating the appearance of blocks without necessarily having a priori knowledge of their locations. The methods described herein attenuate the appearance of these blocks such that the quality of the resultant real-time video, as perceived by the HVS, is improved.
1 . A method for removing artifacts from an image frame, said artifacts being visually disruptive to the HVS, said method comprising:
separating a digital representation of each image frame into a Deblock region that is to be deblocked and a Detail region that is to remain essentially undeblocked.
2 . The method of claim 1 further comprising:
smoothing said Deblock region of each said image frame; and
combining said smoothed Deblock region with said unblocked Detail region to form an a new image frame having less visual disruption to the HVS than a pre-separated image frame.
3 . The method of claim 2 wherein said separating comprises at least one of the following criteria for determining said Deblock Region: intensity-flatness; discontinuity; look-head; look-behind.
4 . The method of claim 3 wherein parameters of said criteria are chosen such that attenuation occurs for compressed image frames in which locations of artifact blocks are a priori unknown.
5 . The method of claim 4 wherein said artifact blocks occur in said compressed video frames due to one or more of the following: previously compressed multiple times; re-formatted image frames, color-mixed image frames; re-sized image frames.
6 . The method of claim 3 wherein said intensity-flatness criteria employs statistical measures comprising a local variance and a local mean of intensities.
7 . The method of claim 3 wherein intensity change criteria are based on fractional changes of intensity.
8 . The method of claim 2 wherein said smoothing comprises:
spatial smoothing to attenuate said Deblock Region.
9 . The method of claim 2 wherein said smoothing comprises attenuation of blocks as well as other artifacts in said Deblock Region.
10 . The method of claim 1 where said separating occurs within a DCT-based encoder.
11 . The method of claim 2 wherein said smoothing comprises at least one of:
FIR filters, IIR filters.
12 . The method of claim 11 wherein said filters can be either spatially-variant or spatially invariant.
13 . The method of claim 11 wherein said smoothing comprises:
at least one Moving Average FIR 2D Box filter.
14 . The method of claim 2 wherein said smoothing comprises:
means for ensuring that smoothing does not occur outside of the boundaries of said Deblock Region.
15 . The method of claim 1 wherein said separating recursively separates said image frame into Deblock Regions and Detail Regions.
16 . The method of claim 1 wherein said separating comprises:
selecting candidate regions; and
determining on a selected candidate by selected candidate region basis whether a selected candidate region belongs to said Deblock region according to certain criteria.
17 . The method of claim 16 wherein said candidate regions are sparsely located in each image frame.
18 . The method of claim 17 wherein a separated Detail region is expanded to allow spatially invariant filtering of said Deblock region without causing a halo effect around said Detail Region.
19 . The method of claim 18 wherein said expansion comprises:
growing each candidate pixel to a surrounding rectangle of pixels.
20 . The method of claim 1 wherein a separated Detail region is expanded to allow spatially invariant filtering of said Deblock region without causing a halo effect around said Detail Region.
21 . The method of claim 2 wherein said smoothing comprises:
use of an N-pixel crossed-mask.
22 . The method of claim 21 where N equals 9.
23 . The method of claim 2 wherein said smoothing comprises:
using dilated crossed-masks for Deblocking video signals having spread out edge discontinuities.
24 . A system for presenting video, said system comprising:
an input for obtaining a first video frame having a certain number of bits per pixel;
said certain number being such that when said video frame is presented to a display said display yields artifacts perceptible to a human visual system (HVS); and
circuitry for producing a second video frame from said first video frame, said second video frame yielding artifacts less perceptible to said HVS when said second video frame is presented to said display.
25 . The system of claim 24 wherein said certain number extends to a low of 0.1 bits/pixel.
26 . The system of claim 24 wherein said certain number is a number of bits/pixel provided by compression of said first video frame using an H.264 encoder.
27 . The system of claim 25 wherein said certain number is at least ½ the number of bits achieved by an H.264 encoder.
28 . The system of claim 24 wherein said producing circuitry comprises:
means for separating said video frame into a Detail region and a Deblock region; and
means for smoothing said Deblock region prior to combining said regions to form said second video frame.
29 . The system of claim 28 further comprising:
a tuner for allowing a user to select one of a plurality of digital video streams, each said video stream comprising a plurality of digital video frames.
30 . The system of claim 28 wherein said smoothing comprises:
a spatially invariant FIR filter having a certain crossed-mask size; and
a processor for preventing said spatially invariant filter from smoothing said Detail regions.
31 . The system of claim 30 wherein said processor operates to expand said Detail regions a distance approximately equal to ½ said crossed-mask size.
32 . The system of claim 28 wherein said smoothing means comprises:
a spatially variant FIR filter.
33 . The system of claim 28 wherein said separating means comprises:
processing using at least one of the following criteria for determining said Deblock Region: intensity-flatness; discontinuity; look-head; look-behind.
34 . The system of claim 33 wherein parameters of said criteria are chosen such that artifact attenuation occurs for compressed image frames in which locations of artifact blocks are a priori unknown.
35 . The system of claim 34 wherein said artifact blocks occur in said compressed video frames due to one or more of the following: previously compressed multiple times; re-formatted image frames, color-mixed image frames; re-sized image frames.
36 . The system of claim 33 wherein said intensity-flatness criteria employs statistical measures comprising a local variance and a local mean of intensities.
37 . The system of claim 33 wherein intensity change criteria are based on fractional changes of intensity.
38 . The system of claim 28 wherein said smoothing means comprises:
a processor operative for spatial smoothing to attenuate said Deblock Region.
39 . The system of claim 28 wherein said smoothing means comprises:
a processor for attenuating blocks as well as other artifacts in said Deblock Region.
40 . The system of claim 28 where said means for separating is a portion of a DCT-based encoder.
41 . The system of claim 28 wherein said smoothing means comprises at least one of: FIR filters, IIR filters.
42 . The system of claim 41 wherein said filters can be either spatially-variant or spatially invariant.
43 . The system of claim 28 wherein said smoothing means comprises:
at least one Moving Average FIR 2D Box filter.
44 . The system of claim 28 wherein said separating means recursively separates said image frame into Deblock Regions and Detail Regions.
45 . The system of claim 28 wherein said separating means comprises:
means for selecting candidate regions; and
means for determining on a selected candidate by selected candidate region basis whether a selected candidate region belongs to said Deblock region according to certain criteria.
46 . The system of claim 45 wherein said candidate regions are sparsely located in each image frame.
47 . A method of presenting video, said method comprising:
obtaining a first video frame having a certain number of bits per pixel; said certain number being such that when said video frame is presented to a display said display yields artifacts perceptible to a human visual system (HVS); and
producing a second video frame from said first video frame, said second video frame yielding artifacts less perceptible to said HVS when said second video frame is presented to said display.
48 . The method of claim 47 wherein said certain number extends to a low of 0.1 bits/pixel.
49 . The method of claim 47 wherein said producing comprises:
separating Detail and Deblock regions within each said frame; and
smoothing said Deblock region; and
combining said smoothed Deblock region with said separated Detail region.
50 . The method of claim 49 wherein said smoothing comprises:
using a spatially invariant FIR filter having a certain crossed-mask size; and
expanding said Detail region a distance at least equal to ½ said crossed-mask size so as to avoid a halo effect at a border between said Deblock and Detail regions.
51 . The method of claim 50 further comprising:
receiving at a device a plurality of digital video streams, each said stream having a plurality of said digital video frames; and
wherein said obtaining comprises:
selecting one of said received digital video streams at said device.