Gain controlled threshold in denoising filter for image signal processing
View Patent ↗An image processing system is disclosed which uses gain information from an input image to determine a threshold value used to filter the input image. The gain information is indicative of the amount of illumination of the input image and thus the noise level. The image processing system includes an image processor, a converter and a filter. The image processor receives and processes first image information into second image information and extracts the gain information from the first image information. The converter converts the gain information into a filter threshold, which is used by the filter to filter the second image information to provide filtered image information. The converter may include a lookup table storing noise characteristic estimates or the threshold values. The threshold values may further be based on subband size. The filter may be a wavelet-based transform denoising filter.
1. An image processing system, comprising:
an image processor which receives first image information amplified using first gain information, which processes said first image information into second image information, which extracts second gain information from said first image information, and which updates said first gain information using said second gain information to provide updated gain information;
a converter which converts said updated gain information into a filter threshold; and
a filter which filters said second image information using said filter threshold to provide filtered image information.
2. The image processing system of claim 1 , wherein said updated gain information comprises analog and digital gain information.
3. The image processing system of claim 1 , wherein said image processor comprises:
a statistics circuit which determines color component statistics from said first image information;
a color processing circuit which determines luminance information from said first image information;
a luminance circuit which determines light intensity information from said luminance information; and
a white balance and exposure control circuit which uses said color component statistics and said light intensity information to update said first gain information.
4. The image processing system of claim 1 , further comprising:
said converter further providing a select value based on said updated gain information;
select logic which selects between said second image information and said filtered image information based on said select value; and
wherein said select value causes said select logic to select said filtered image information when said gain information indicates an illumination level below an illumination threshold.
5. The image processing system of claim 1 , wherein said converter comprises a lookup table storing a plurality of filter threshold values based on said updated gain information.
6. The image processing system of claim 1 , wherein said converter comprises:
a lookup table storing a plurality of noise characteristic estimates based on said updated gain information; and
a threshold circuit which multiplies a selected one of said plurality of noise characteristic estimates provided from said lookup table by a multiple based on a subband size to provide said filter threshold.
7. The image processing system of claim 1 , wherein said converter comprises an arithmetic calculation circuit which converts said updated gain information into a total gain, and which converts said total gain into a noise characteristic estimate.
8. The image processing system of claim 1 , wherein said filter comprises a wavelet-based denoising filter.
9. The image processing system of claim 1 , wherein said filter comprises:
a forward discrete wavelet transform filter having an input receiving said second image information and an output providing wavelet values;
a threshold circuit having a first input receiving said wavelet values, a second input receiving said filter threshold, and an output providing adjusted wavelet values; and
an inverse discrete wavelet transform filter having an input receiving said adjusted wavelet values and an output providing said filtered image information.
10. The image processing system of claim 9 , wherein said threshold circuit replaces each wavelet value that is less than said filter threshold with a zero value coefficient.
11. A method of processing image information, comprising:
processing first image information amplified using first gain information into second image information;
during said processing, determining second gain information from the first image information;
updating the first gain information using the second gain information and providing updated gain information;
converting the updated gain information into a filter threshold; and
filtering the second image information using the filter threshold to provide filtered image information.
12. The method of claim 11 , wherein said determining second gain information comprises determining analog gain information and digital gain information.
13. The method of claim 11 , wherein said determining second gain information comprises:
determining color component statistics from the first image information;
determining luminance information from the first image information;
determining light intensity information from the luminance information; and
determining the second gain information from the color component statistics and the light intensity information.
14. The method of claim 11 , further comprising:
selecting the filtered image information when the updated gain information indicates an illumination level below a predetermined illumination threshold; and
selecting the second image information when the updated gain information indicates an illumination level above the predetermined threshold.
15. The method of claim 11 , wherein said converting comprises providing the updated gain information to a lookup table storing a plurality of filter thresholds.
16. The method of claim 11 , wherein said converting comprises:
providing the updated gain information to a lookup table storing a plurality of gamma values; and
determining the filter threshold based on a selected gamma value and a subband size.
17. The method of claim 11 , wherein said converting the updated gain information comprises determining a total gain value from the updated gain information and converting the total gain value into a gamma value.
18. The method of claim 11 , wherein said filtering comprises:
transforming the second image information into wavelet values;
replacing wavelet values that are less than the filter threshold with a zero value and otherwise passing the wavelet values to provide adjusted wavelet values; and
transforming the adjusted wavelet values into the filtered image information.
19. An image processing system, comprising:
an image sensor providing raw image information;
gain circuitry which amplifies and digitizes said raw image information to provide gain adjusted image information using first gain information;
an image processor which processes said gain adjusted image information into processed image information, and which extracts second gain information from said gain adjusted image information, and which updates said first am information using said second gain information and provides updated gain information;
a converter which converts said updated gain information into a filter threshold; and
a denoising filter which filters said processed image information using said filter threshold to provide filtered image information.
20. A method of processing image information, comprising:
processing first image information into second image information;
during said processing, determining gain information from the first image information;
converting the gain information into a filter threshold;
filtering the second image information using the filter threshold to provide filtered image information;
selecting the filtered image information when the gain information indicates an illumination level below a predetermined illumination threshold; and
selecting the second image information when the gain information indicates an illumination level above the predetermined threshold.