Method for processing highlights and saturated regions in a digital image
A method for performing highlight restoration on a digital image includes comparing the pixels in the image with a saturation level value to identify saturated pixels. A saturation map of saturated pixels is generated. Each selected saturated pixel is identified as a restorable pixel only if at least one color channel of the pixel is unsaturated. For each restorable pixel, a group of the closest unsaturated pixels above, below, to the left, and to the right of the select saturated pixel is identified. A replacement pixel value is generated for each saturated color channel of the restorable pixel, using a combination of the pixel values of the unsaturated color channels of the restorable pixel and the pixel values of the corresponding color channels of the nearby unsaturated pixels.
1. A method for performing at least one of highlight restoration and highlight neutralization of an image from a digital camera, comprising:
generating a blending value within a predetermined range;
if the blending value is equal to a minimum in the predetermined range, performing highlight restoration;
if the blending is equal to a maximum in the predetermined range, performing highlight neutralization;
if the blending value is between the minimum and the maximum in the predetermined range, performing both highlight restoration and highlight neutralization, and blending the results of the highlight restoration and highlight neutralization according to the blending value; and
comparing values returned by the highlight restoration with a predetermined threshold, and performing highlight neutralization instead if the returned values fall below the predetermined threshold.
2. The method of claim 1 wherein the predetermined range of the blending value is between zero and one.
3. The method of claim 1 , wherein generating the blending value comprises determining the blending value by the user.
4. The method of claim 1 , wherein generating the blending value comprises:
generating a reference exposure value as a function of the camera capture parameters; and
comparing a reference exposure value and the actual exposure value.
5. The method of claim 4 , wherein comparing the reference exposure value and the actual exposure value comprises:
determining the difference between the actual exposure value and the reference exposure value; and
scaling the difference between zero and one using at least one predetermined parameter.
6. The method of claim 4 , wherein comparing the reference exposure value and the actual exposure value comprises:
determining the absolute value of the difference between the actual exposure value and the reference exposure value; and
scaling the absolute value of the difference between zero and one using at least one predetermined parameter.
7. The method of claim 4 , wherein comparing the reference exposure value and the actual exposure value comprises:
determining the difference between the actual exposure value and the reference exposure value;
performing the blending operation only if the difference between the actual exposure value and the reference exposure value exceeds a predetermined threshold.
8. The method of claim 4 , wherein comparing the reference exposure value and the actual exposure value comprises:
determining the difference between the actual exposure value and a predetermined optimum exposure value as the reference exposure value; and
performing the blending operation only if the difference between the actual exposure value and the optimum exposure value exceeds a predetermined threshold.
9. The method of claim 1 , wherein performing highlight neutralization comprises:
identifying all pixels in the image having values in all three color channels exceeding a threshold value below the saturation level of the digital camera;
for all pixels in the image identified as having values in all three color channels exceeding the threshold value, moving the pixel value in all three color channels neutral as a function of to how close the values in the three color channels are to the saturation level.
10. The method of claim 9 , further including:
generating a saturation map of the image;
enhancing the saturation map;
smoothing the enhanced saturation map;
generating a neutralization signal as one of the maximum and weighted average of color components in each pixel location;
blending the image with the neutralization signal.