Image detail enhancement system

• US 7,110,044 B2
• Filed: 03/27/2003
• Issued: 09/19/2006
• Est. Priority Date: 03/27/2003
• Status: Expired due to Fees

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Yeong-Taeg, Wang, Xianglin
• Primary Examiner(s): LEE, MICHAEL
• Application Number:
  US10/402,280
• Publication Number:
  US 20040189874A1
• Time in Patent Office: 1,272 Days
• Field of Search: 348/622, 348/623, 348/627, 348/607
• US Class Current: 348/627
• CPC Class Codes: H04N 5/205 for correcting amplitude versus frequency characteristic

Abstract

A detail enhancement system uses a detail filter bank including multiple detail filters covering different frequency ranges. An input video signal representing a digital image is processed in the detail filter, wherein detail signals are extracted by the detail filters at different frequency ranges. Shoot suppression blocks and coring blocks are provided for each detail filter to prevent overshoot/undershoot artifacts and small ringing artifacts, respectively. The overall detail signal is amplitude scaled, and added back to the input signal as an enhancement, to generate a detail enhanced output signal.

Claims

1. A method for image detail enhancement, comprising the steps of:

(a) filtering an input signal representing a digital image, through each of a plurality of detail filters, each filter having a frequency response covering a selected frequency range, wherein the output of each filter forms a detail signal representing an enhancement such that the detail signals are extracted at different frequency ranges;

(b) performing a coring function on each detail signal to generate a detail signal with reduced noise;

(c) determining a shoot suppression factor for each detail signal based on the image characteristics of the image details in order to substantially suppress shoot artifacts in the enhanced image details;

(d) applying each shoot suppression factor to the corresponding noise-reduced detail signal to generate an associated processed detail signal; and

(e) combining the processed detail signals with the input signal to generate enhanced signal representing a detail enhanced image.

2. The method of claim 1, wherein each filter has a frequency range essentially different than that of the other filters.

3. The method of claim 1, wherein one or more of the filters is a high pass filter.

4. The method of claim 1, wherein one or more of the filters is a band pass filter.

5. The method of claim 1, wherein each filter covers a selected frequency range such that the associated output detail signal is in the corresponding frequency range from the input signal.

26. The method of claim 1 wherein performing a coring function on each detail signal further includes the steps of performing a coring function on each detail signal to generate a detail signal with reduced noise and reduced ringing artifacts around edge areas in the image.

6. A method for image detail enhancement, comprising the steps of:

(a) filtering an input sianal representing a digital image, through each of a plurality of detail filters, each filter having a frequency response covering a selected frequency range, wherein the output of each filter fonns a detail signal representing an enhancement;

(b) performing a coring function on each detail signal to generate a detail signal with reduced noise;

(c) determining a shoot suppression factor for each detail signal based on the image characteristics of the image details in order to substantially suppress shoot artifacts in the enhanced image details;

(d) applying each shoot suppression factor to the corresponding noise-reduced detail signal, and multiplying each noise-reduced detail signal by a gain coefficient, to generate an associated processed detail signal; and

(e) combining the processed detail signals with the input signal to generate enhanced signal representing a detail enhanced image.

7. The method of claim 6, wherein one or more of the gain coefficients are adjustable.

8. A method for image detail enhancement, comprising the steps of:

(a) filtering an input signal representing a digital image, through each of a plurality of detail filters, each filter having a frequency response covering a selected frequency range, wherein the output of each filter forms a detail signal representing an enhancement;

(b) performing a coring function on each detail signal to generate a detail signal with reduced noise;

(c) determining a shoot suppression factor for each detail signal based on the image characteristics of the image details in order to substantially suppress shoot artifacts in the enhanced image details;

(d) applying each shoot suppression factor to the corresponding noise-reduced detail signal to generate an associated processed detail signal; and

(e) combining the processed detail signals with the input signal by;

combining the processed detail signals to generate an overall detail signal;

applying amplitude scaling to the overall detail signal to generate a scaled detail signal wherein amplitude of enhancement values above a threshold in the overall detail signal is essentially scaled down; and

combining the scaled detail signal with the input signal to generate an enhanced signal representing a detail enhanced image.

9. The method of claim 8, wherein the relationship between the enhanced signal, J, and the input signal, I, is expressed as:

$J=\mathrm{scaler}(\underset{i=1,2,3}{\sum <br><br>}<br><br>\left(G_i*s_i*{\mathrm{coring}}_i<br><br>\left(f_i<br><br>\left(I\right)\right)\right),$

wherein f_i is a convolution operation performed in a detail filter i,

coring_i is the coring function for each filter,

s_i is the shoot suppression factor for each filter at a current pixel position,

G_i is an adjustable gain coefficient for each detail signal, and

scaler is the scaling function for the amplitude scaling.

10. The method of claim 9, wherein the coring function is expressed as:

$\mathrm{coring}<br><br>\left(x\right)=\{\begin{array}{c}\left(\max <br><br>\left(x,T_c\right)-T_{c<br><br>}\right)*R/\left(R-T_c\right)\\ \left(\min <br><br>\left(x,-T_c\right)+T_c\right)*R/\left(R-T_c\right)\end{array}<br><br>\begin{array}{c}\mathrm{if}<br><br><br><br>x\in <br><br>\left[0,R\right]\\ \mathrm{if}<br><br><br><br>x\in <br><br>\left[-R,0\right)\end{array}$

wherein,

R is an input data dynamic range for the coring function,

T_c is a threshold value for the coring function, such that R and T_c may be different for each coring function depending on the associated detail filter.

11. The method of claim 9, wherein each shoot suppression factor s_i, i=1, 2, 3 is determined by calculating a symmetry factor based on the luminance values of the neighboring image pixels centered with a current image pixel within the filtering range of the corresponding detail filter.

12. The method of claim 9, wherein the scaling function is expressed as:

for values x≧

0,

$\mathrm{scaler}<br><br>\left(x\right)=\{\begin{array}{c}\min <br><br>\left(x,6.0*\ln <br><br>\left(x\right)\right)\\ 0\end{array}<br><br>\begin{array}{c}\mathrm{if}<br><br><br><br>x><br><br>1\\ \mathrm{if}<br><br><br><br>0\le <br><br>x\le <br><br>1\end{array}$

for x<

0,

scaler(x)=−

scaler(−

x).

13. A method for image detail enhancement, comprising the steps of:

(a) filtering an input signal representing a digital image, through each of a plurality of detail filters, each filter having a frequency response covering a selected frequency range, wherein the output of each filter forms a detail signal representing an enhancement;

(b) performing a coring function on each detail signal to generate a detail signal with reduced noise;

(c) determining a shoot suppression factor for each detail signal based on the image characteristics of the image details in order to substantially suppress shoot artifacts in the enhanced image details;

(d) applying each shoot suppression factor to the corresponding noise-reduced detail signal to generate an associated processed detail signal; and

(e) combining the processed detail signals with the input signal by;

applying amplitude scaling to each processed detail signal to generate a scaled detail signal wherein amplitude of enhancement values above a threshold in each processed detail signal is essentially scaled down; and

combining the scaled detail signals with the input signal to generate an enhanced signal representing a detail enhanced image.

14. An image detail enhancement device for enhancing digital video image represented by an input signal, comprising:

a plurality of filters, each filter having a frequency response covering a frequency range, the input signal separately filtered by each filter to generate a corresponding detail signal representing an enhancement;

a plurality of coring blocks corresponding to the plurality of filters, each coring block reducing noise in a detail signal to generate a corresponding noise-reduced detail signal;

a plurality of shoot suppressors corresponding to the plurality of filters, each shoot suppressor determining a shoot suppression factor for each corresponding detail signal based on the image characteristics of the image details in order to substantially suppress shoot artifacts in the enhanced image details;

a plurality of combiners corresponding to the plurality of filters, wherein each combiner applies each shoot suppression factor to the corresponding noise-reduced detail signal to generate an associated processed detail signal; and

a junction device that combines the processed detail signals with the input signal to generate an enhanced signal representing a detail enhanced image.

15. The image detail enhancement device of claim 14, wherein each filter has a frequency range essentially different than that of the other filters.

16. The image detail enhancement device of claim 14, wherein one or more of the filters is a high pass filter.

17. The image detail enhancement device of claim 14, wherein one or more of the filters is a band pass filter.

18. The image detail enhancement device of claim 14, wherein each filter covers a selected frequency range such that the associated output detail signal is in the corresponding frequency range from the input signal.

19. The image detail enhancement device of claim 14, wherein each combiner comprises a multiplier, such that each multiplier multiplies each corresponding noise-reduced detail signal by a gain coefficient before multiplication with the corresponding shoot suppression factor.

20. The image detail enhancement device of claim 19, wherein one or more of the gain coefficients are adjustable.

21. The image detail enhancement device of claim 14, further comprising:

a junction node that combines the processed detail signals to generate an overall detail signal;

an amplitude scaler that applies amplitude scaling to the overall detail signal to generate a scaled detail signal wherein amplitude of enhancement values above a threshold in the overall detail signal is essentially scaled down;

such that the junction device combines the scaled detail signal with the input signal to generate an enhanced signal representing a detail enhanced image.

22. The image detail enhancement device of claim 21, wherein the relationship between the enhanced signal, J, and the input signal, I, is expressed as:

$J=\mathrm{scaler}(\underset{i=1,2,3}{\sum <br><br>}<br><br>\left(G_i*s_i*{\mathrm{coring}}_i<br><br>\left(f_i<br><br>\left(I\right)\right)\right),$

wherein f_i is a convolution operation performed in a filter i,

coring_i is the coring function of each coring block,

s_i is the shoot suppression factor determined by each shoot suppressor at a current pixel position,

G_i is an adjustable gain coefficient for each detail signal, and

scaler is the scaling function of the amplitude scaler.

23. The image detail enhancement device of claim 22, wherein the coring function is expressed as:

$\mathrm{coring}<br><br>\left(x\right)=\{\begin{array}{c}\left(\max <br><br>\left(x,T_c\right)-T_{c<br><br>}\right)*R/\left(R-T_c\right)\\ \left(\min <br><br>\left(x,-T_c\right)+T_c\right)*R/\left(R-T_c\right)\end{array}<br><br>\begin{array}{c}\mathrm{if}<br><br><br><br>x\in <br><br>\left[0,R\right]\\ \mathrm{if}<br><br><br><br>x\in <br><br>\left[-R,0\right)\end{array}$

wherein,

R is an input data dynamic range for the coring function,

T_c is a threshold value for the coring function, such that R and T_c may be different for each coring function depending on the associated detail filter.

24. The image detail enhancement device of claim 22, wherein each shoot suppression factor s_i, i=1, 2, 3 is determined by calculating a symmetry factor based on the luminance values of the neighboring image pixels centered with a current image pixel within the filtering range of the corresponding detail filter.

25. The image detail enhancement device of claim 22, wherein the scaling function is expressed as:

for values x≧

0,

$\mathrm{scaler}<br><br>\left(x\right)=\{\begin{array}{c}\min <br><br>\left(x,6.0*\ln <br><br>\left(x\right)\right)\\ 0\end{array}<br><br>\begin{array}{c}\mathrm{if}<br><br><br><br>x><br><br>1\\ \mathrm{if}<br><br><br><br>0\le <br><br>x\le <br><br>1\end{array}$

for x<

0,

scaler(x)=−

scaler(−

x).