Image Contrast and Sharpness Enhancement

• US 20080187236A1
• Filed: 03/01/2006
• Published: 08/07/2008
• Est. Priority Date: 03/03/2005
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Der Heijden, Henricus Wilhelm Peter
• Application Number:
  US11/816,757
• Publication Number:
  US 20080187236A1
• Time in Patent Office: Days
• US Class Current: 382/263
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20021 Dividing image into blocks, subimages or windows
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/10 using non-spatial domain filtering
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction

Abstract

The invention relates to a method for image enhancement. Overshoots of image boosting in areas with edges can be prevented by splitting an image into at least three sub-images, wherein each of the sub-images represents a corresponding spatial frequency range of the image, calculating a pixel detail signal for at least one of the sub-images, depending on at least a pixel detail signal of another frequency range, calculating a pixel change value for pixels within the sub-images depending on the corresponding pixel detail signal, calculating changed sub-images by changing pixel values within the sub-images depending on the corresponding pixel change value, and combining the changed sub-images into an output image.

Claims

1. Method for changing pixel values within images with

splitting an image into at least three sub-images, wherein each of the sub-images represents a corresponding spatial frequency range of the image,

calculating a pixel detail signal for at least one of the sub-images, depending on at least a pixel detail signal of another frequency range,

calculating a pixel change value for pixels within the sub-images depending on the corresponding pixel detail signal,

calculating changed sub-images by changing pixel values within the sub-images depending on the corresponding pixel change value, and

combining the changed sub-images into an output image.

2. Method of claim 1, wherein calculating the pixel detail signal comprises calculating a cumulative pixel detail signal depending on at least a pixel detail signal of a neighbouring frequency range.

3. The method of claim 1, wherein calculating a pixel detail signal comprises calculating a maximum pixel value within an aperture of K×

L pixels of a pixel detail signal within another frequency range, the aperture surrounding the corresponding pixel.

4. The method of claim 3, wherein the pixel detail signal is up-sampled before calculating the maximum pixel value.

5. The method of claim 3, further comprising down-sampling the pixel detail signal after calculating the maximum pixel value.

6. Method of claim 1, wherein calculating the pixel change value comprises decreasing the pixel change value with an increased cumulative pixel detail signal.

7. Method of claim 6, wherein calculating the pixel change value comprises calculating

$g_i=1+\left(f-1\right)$

MAX 

( T - CATS i T , 0 )

with g the pixel change value, f a gain factor, T a threshold value, CATS the pixel detail signal, and i an integer representing the corresponding frequency range.

8. Method of claim 1, further comprising calculating derived sub-images for at least one of the at least three sub-images.

9. The method of claim 8, wherein calculating the derived sub-images comprises combining at least two sub-image within different frequency ranges.

10. The method of claim 8, wherein calculating the pixel detail signal as

CATS_i=abs D_i(x,y)+max CATS_i-1

with CATS the pixel detail signal, D the derived sub-image, x, y pixel co-ordinates, and i an integer denoting the corresponding frequency range.

11. The method of claim 8, wherein the pixel detail signal for the highest frequency range is the absolute value of the first derived sub-image.

12. The method of claim 1, wherein splitting the image into at least three sub-images comprises applying at least a spatial low-pass filtering iteratively.

13. The method of claim 12, further comprising down-sampling the low-pass filtered image after low-pass filtering.

14. The method of claim 1, wherein combining the changed sub-images into an output image comprises calculating a summed value of the changed sub-images and the sub-image in the lowest frequency range.

15. The method of claim 1, wherein combining the changed sub-images into an output images comprises up-sampling the changed sub-images to the pixel grid of the input image.

18. Use of a method of claim 1 in image processing, video processing, television displays, computer displays.

16. Image enhancing device with

first filter means arranged for splitting an image into at least three sub-images, wherein each of the sub-images represents a corresponding spatial frequency range of the image,

first combination means arranged for calculating a pixel detail signal for at least one of the sub-images, depending on at least a pixel detail signal of another frequency range,

second combination means arranged for calculating a pixel change value for pixels within the sub-images depending on the corresponding pixel detail signal,

calculation means arranged for calculating changed sub-images by changing pixel values within the sub-images depending on the corresponding pixel change value, and

third combination means arranged for combining the changed sub-images into an output image.

17. A computer program product tangibly embodied in an information carrier, the computer program product comprising instructions that, when executed, cause at least one processor to perform operations comprising:

splitting an image into at least three sub-images, wherein each of the sub-images represents a corresponding spatial frequency range of the image,

calculating a pixel detail signal for at least one of the sub-images, depending on at least a pixel detail signal of another frequency range,

calculating a pixel change value for pixels within the sub-images depending on the corresponding pixel detail signal,

calculating changed sub-images by changing pixel values within the sub-images depending on the corresponding pixel change value, and

combining the changed sub-images into an output image.