Blur and Sharpen
I took this picture of a spectacular mammatocumulus display using the film that
happened to be in my camera, Fuji NPH 400. The grain was more than I expected,
particularly in the relatively neutral clouds. Here you see the unretouched
scan.
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My challenge was to eliminate the grain in the clouds while preserving the
detail in the trees. Here are the steps I used.
- Since the trees are relatively silhouetted against the sky, I created a
mask from the coverage of the trees. I did this by increasing the contrast
and adjusting brightness until I had a hard edged mask. Because of the varying
brightness around the several areas of the trees, I performed this task
separately for each group of trees.
- Through trial and error, I figured out that the mask was not good enough.
I used an erode filter to expand the mask a bit, and then I applied a gaussian
blur with radius 3 to the mask. This was to soften the transition between
sharpened/blurred areas of the final image.
- I applied this mask to the unretouched image and applies a gaussian blur to
the image, again with a radius of 3, through the mask.
- I inverted the mask and applied an unsharpen filter to the leaves of the
trees.
Here is the result of applying this procedure.
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