Correcting uneven exposure across an image

Comments and discussions about 8bf plugins which can be use in various applications like Photoshop, Paint Shop Pro or Photo-Paint
Phil Hanley
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Correcting uneven exposure across an image

Postby Phil Hanley » Fri Jul 28, 2006 10:30 am

I have a number of pictures taken with a cheap digital camera, where there is a graduation across the picture such that towards the edge of the image to one side it comes out as increasingly under-exposed as compared with the rest of the image. Is there a plug-in that can correct this problem? Playing around with the various settings does show that the information is there in the image, but as far as I can see the basic Photoshop7 will only apply these globally, to the whole image, so that this graduation is not filtered out.

Ilya Razmanov
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Postby Ilya Razmanov » Fri Jul 28, 2006 12:51 pm

I have the plugin that may help:

http://photoshop.msk.ru/aspd/

but it ain't free. Also, you may try playing with this:

http://photoshop.msk.ru/as/highpass.html

and see if free part of it functionality is sufficient for your needs.

And obviously, both of them will work only if you <i>really</i> have some useful signal in over\underexposed areas of your image. If they are like flat pure white\black areas, no software will recover the signal which is not there.

HaraldHeim
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Postby HaraldHeim » Fri Jul 28, 2006 3:30 pm

You can fix it by dublicating the image on a new layer, adding a layer mask, drawing a gradient on the layer mask with the gradient tool and the adjusting the brightness of the new layer with the Levels tool.

I hope that helps.

Ilya Razmanov
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Postby Ilya Razmanov » Wed Aug 02, 2006 3:17 pm

HaraldHeim wrote:You can fix it by dublicating the image on a new layer, adding a layer mask, drawing a gradient on the layer mask with the gradient tool and the adjusting the brightness of the new layer with the Levels tool.


Frankly, that's the rare case I'd disagree with you, at least to some degree :-) Unwanted signal in such an images rarely seem to be fully and properly approximated by simple linear gradient; normally, it's more complicated. So, while the technique you described will improve the quality to some degree, IMHO even dumb frequency filtering like highpass can often do better. Not to mention, it is likely to take less user efforts since frequency filtering don't care of gradient direction and stuff.

Just my personal opinion, nothing more :-)


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