Almost
every image has a degree of vignetting that must be removed at some
point during post-processing. There are many ways to do this,
each with its pros and cons. I have tried almost all of them, and
have concluded that the best and easiest is the "Background
Compensation" feature present in ImagesPlus. I am not affiliated
with ImagesPlus in any way, and suggest that you check Mike Unsold's
website
for further details.
(Please click on image for a higher
resolution view)
Steps (assumes some familiarity
with ImagesPlus):
1. Open the desired image that has been stretched in step 2 (the
fact that it has been stretched will make it easier to detect
vignetting).
2. Open the Line Profile box; Open the Background Compensation
box.
3. Select the "Background Maximum" point.
4. Draw a line that passes through the region of uneven
luminosity (a diagonal was used in this example).
5. Examine the Line Profile curve- you can see that it gradually
rises towards the center and then falls, reflecting the distribution of
uneven luminosity. This is what requires correction, or
"flattening".
6. Using the Guassian option, adjust the Amplitude and Scale
parameters to achieve the desired result, shown here:
(Please
click on image for a higher resolution view)
7.
Save this corrected file in 16 bit TIFF format for use in
subsequent steps.
