Enhancing images
A method of enhancing an image includes constructing an input histogram corresponding to an input image received at a focal plane array, the input histogram representing a pixel intensity distribution corresponding to the input image and performing an analytical operation on the input histogram to produce a modified cumulative distribution, wherein the analytical operation is a function of camera temperature. The input image is transformed using the modified cumulative distribution to produce an enhanced output image corresponding to the input image, wherein at least a portion of the input image is enhanced in the output image. In addition to or in lieu of the non-linear operation, the binning edges of the input histogram can be adjusted based on at least one of camera temperature and sensitivity state to construct an adjusted cumulative distribution.
1. A method of enhancing an image comprising:
constructing an input histogram corresponding to an input image received at a focal plane array, the input histogram representing a pixel intensity distribution corresponding to the input image;
performing an analytical operation on the input histogram to produce a modified histogram, wherein the analytical operation is a function of camera temperature, wherein performing an analytical operation includes receiving camera temperature data and using the camera temperature; and
transforming the input image using a cumulative distribution of the modified histogram to produce an enhanced output image corresponding to the input image, wherein at least a portion of the input image is enhanced in the output image, wherein performing an analytical operation includes calculating a power of the input histogram to produce a resulting histogram, wherein performing the analytical operation includes multiplying the resulting histogram by a ramp function in a non-linear operation expressed as
RAMP_NORM=( X +ENH_RAMP)/(1+ENH_RAMP)
and
RAMP_LUT=MAX_BIN*RAMP_NORM,
With
X =([0:MAX_BIN]−OFFSET( T ))/(CLIP( T )−OFFSET( T )),
wherein
if X<0 then X=0,
if X>1 then X=1;
wherein OFFSET(T) is the temperature dependent minimum input histogram level, CLIP(T) is the temperature dependent maximum input histogram level, ENH_RAMP is slope adjustment, RAMP_NORM is the normalized ramp function, RAMP_LUT is the look-up table for the ramp calculation, MAX_BIN is the maximum value of the cumulative LUT bin, wherein the non-linear operation is a function of the camera temperature;
and
adjusting binning edges of the input histogram based on the camera temperature and sensitivity state to construct an adjusted histogram, wherein performing an analytical operation on the input histogram includes performing the analytical operation on the adjusted histogram to produce the modified histogram.
2. A method as recited in claim 1 , wherein adjusting the binning edges includes receiving camera temperature data and using the camera temperature to adjust the binning edges.
3. A method as recited in claim 1 , further comprising receiving the input image from the focal plane array wherein the focal plane array is allowed to vary in temperature.