Method and apparatus for visual perception encoding

• US 6,744,818 B2
• Filed: 12/27/2000
• Issued: 06/01/2004
• Est. Priority Date: 12/27/2000
• Status: Expired due to Term

• Current Assignee: DigiMedia Tech, LLC (IP Investments Group LLC)
• Original Assignee: VLS Com Ltd
• Inventors: Sheraizin, Vitaly S., Sheraizin, Semion M.
• Primary Examiner(s): LEE, Y YOUNG
• Application Number:
  US09/748,248
• Publication Number:
  US 20020122494A1
• Time in Patent Office: 1,252 Days
• Field of Search: H04/N.712, 375/240, 375/240.01, 375/240.16, 375/240.29, 382/264, 704/229, 704/500
• US Class Current: 375/240.29
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression

Abstract

A video encoding system includes a visual perception estimator, an encoder, a compression dependent threshold estimator and a filter unit. The visual perception estimator estimates a perception threshold for a pixel of a current frame of a videostream. The encoder encodes the current frame. The compression dependent threshold estimator estimates a compression dependent threshold for the pixel at least from the perception threshold and information from the encoder. The filter unit filters the pixel at least according to the compression dependent threshold.

Claims

1. A video encoding system comprising:

a visual perception estimator adapted to estimate a perception threshold for a pixel of a current frame of a videostream;

an encoder adapted to encode said current frame;

a compression dependent threshold estimator adapted to estimate a compression dependent threshold for said pixel at least from said perception threshold and information from said encoder; and

a filter unit adapted to filter said pixel at least according to said compression dependent threshold.

2. A system according to claim 1 and wherein said compression dependent threshold estimator also estimates at least one parameter from the following group of parameters:

whether or not a new frame NwFr has been defined by said encoder as an I frame;

whether an ith pixel is in the foreground FG or the background BG of a picture;

whether an ith pixel forms part of an edge Ed around an object in the picture;

whether or not the ith pixel forms part of a single detail SD;

whether or not the ith pixel is part of a group Gr of generally periodic details;

the contrast level Lv of the detail for the ith pixel;

the duration τ

of a detail within a picture;

how full said encoder is; and

the distance DP of the ith pixel from the center of the frame.

3. A system according to claim 2 and wherein said compression dependent threshold is formed from normalized versions of said parameters and said perception threshold PTHD_i as follows:

${\mathrm{CTHD}}_i=\left(\begin{array}{c}{\mathrm{PTHD}}_i+C_E<br><br>\mathrm{Ed}+C_D<br><br>\mathrm{SD}+C_G<br><br>\mathrm{Gr}+C_r<br><br>N<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\tau <br><br>}+\\ C_L<br><br>\mathrm{NLv}+C_F<br><br>\mathrm{NwFr}+C_B<br><br>F/B+C_P<br><br>\mathrm{DP}\end{array}\right)<br><br>C_V<br><br>\mathrm{VBF}+C_0$

where C_B, C_D . . . , C_P are weighting coefficients.

4. A system according to claim 1 and wherein said filter unit is a controllable filter set adapted to select a filter for said pixel according to said compression dependent threshold.

5. A system according to claim 1 and wherein said filter unit is a non-linear filter.

6. A system according to claim 5 wherein said non-linear filter comprises:

a low pass filter;

a high pass filter whose output is a signal Δ

Y_HF;

a first switch SW1 whose output is defined as;

$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{SW1}}=\{\begin{array}{cc}2<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{HF}}-\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y^2<br><br>\mathrm{HF}}{3<br><br>\mathrm{\sigma <br><br>}},& \mathrm{if}<br><br><br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{HF}}<br><br><<br><br>3<br><br>\mathrm{\sigma <br><br>}\\ 3<br><br>\mathrm{\sigma <br><br>},& \mathrm{otherwise}\end{array}$

where σ

is the root-mean-squared (RMS) noise level of the input signal to said filter unit;

a second switch SW2 whose output is defined as;

$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{SW2}.}=\{\begin{array}{cc}\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{HF}}^2}{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{CTHD}}},& \mathrm{if}<br><br>\text{\hspace{1em}<br><br>}<br><br><br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{HF}}<br><br>\le <br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{CTHD}}\\ \mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{CTHD}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_{\mathrm{SL}},& \mathrm{otherwise}\end{array}$

where Δ

Y_CTHD is the signal level that corresponds to the compression dependent threshold CTHD and Δ

Y_SL is defined as;

7. A system according to claim 1 and wherein said filter unit includes at least one nonlinear filter unlit and a chrominance correction unit.

8. A system according to claim 7 and wherein said chrominance correction unit includes means for maintaining the ratio of two chrominances C_r and C_b to luminance Y.

9. A system according to claim 1 and also comprising a resolution enhancing filter which generally enhances the resolution of the output of said filter unit.