Camera noise reduction for machine vision systems
A method for reducing noise in an image from an image capture device includes filter the image using both an offset fixed pattern noise filter and a gain fixed pattern noise filter. Thereafter, the image is filtered using a remnant fixed pattern noise filter to reduce remnant fixed pattern noise.
1. A method for reducing noise in an image from an image capture device comprising:
(a) receiving an image from an image capture device;
(b) processing said image in a manner to reduce offset fixed pattern noise in said image using a random noise suppressed, two-dimensional model of offset fixed pattern noise from said image capture device;
(c) processing said image in a manner to reduce gain fixed pattern noise in said image using a random noise suppressed, two-dimensional model of gain fixed pattern noise from said image capture device;
(d) filtering said filtered image as a result of step (b) and step (c) using a remnant fixed pattern noise filter to reduce remnant fixed pattern noise.
2. The method of claim 1 further comprising the step of filtering said filtered image as a result of step (d) using a shot noise filter.
3. The method of claim 2 further comprising the step of filtering said filtered image as a result of step (d) using a readout noise filter.
4. The method of claim 1 wherein said processing of said image to reduce offset fixed pattern noise uses a predetermined characterization of said image capture device.
5. The method of claim 1 wherein said processing said image to reduce gain fixed pattern noise uses a predetermined characterization of said image capture device.
6. The method of claim 1 wherein said filtering of said image using said remnant fixed pattern noise filter does not use a predetermined characterization of said image capture device.
7. The method of claim 4 wherein said filtering of said image using said remnant fixed pattern noise filter does not use a predetermined characterization of said image capture device.
8. The method of claim 5 wherein said filtering of said image using said remnant fixed pattern noise filter does not use a predetermined characterization of said image capture device.
9. The method of claim 3 wherein said readout noise is generally signal-independent noise with zero mean.
10. The method of claim 2 wherein said shot noise is signal-dependent with a variance that depends on the signal value at a particular pixel location.
11. The method of claim 1 wherein said remnant fixed pattern noise has the characteristic of generally isolated spikes that have at least one of a significantly higher value and lower value than its surrounding pixels.
12. The method of claim 11 wherein said remnant fixed pattern noise filter uses a rank conditioned rank selection filter.
13. The method of claim 12 wherein said filter uses an additional condition for classifying a pixel as a noise spike.
14. The method of claim 13 wherein said additional condition requires the difference between said pixel and surrounding pixels to be larger than a threshold.
15. The method of claim 14 wherein said filter is characterized by
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where {circumflex over (f)} c is a filtered value of a target pixel, f i is the value of the i th pixel in a matrix about said target pixel r i is the i th ranked value in said matrix, and T RCM is a threshold.
16. A method for reducing noise in an image from an image capture device comprising:
(a) receiving an image from an image capture device;
(b) processing said image in a manner to reduce offset fixed pattern noise in said image;
(c) processing said image in a manner to reduce gain fixed pattern noise in said image; and
(d) filtering said filtered image as a result of step (b) and step (c) using a remnant fixed pattern noise filter to reduce remnant fixed pattern noise, wherein said remnant fixed pattern noise filter is a rank conditioned rank selection filter characterized by
f
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c
←
{
r
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if
(
f
5
=
r
1
)
⋀
(
r
2
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1
>
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RCM
)
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)
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otherwise
;
where {circumflex over (f)} c is a filtered value of a target pixel, f i is the value of the i th pixel in a matrix about said target pixel r i is the i th ranked value in said matrix, and T RCM is a threshold.