Help me fix my dusty holiday pictures.
November 21, 2010 11:07 AM   Subscribe

Some of the pictures I took on my last holiday have turned out to have fairly obvious dark smudges. Seems like my trusty point and shoot digital camera has a bad case of dust on the sensor and will need servicing, but is there anything I can do software-wise to salvage the pictures?

I just came back from a late holiday in sunny Cádiz to find that some of my pictures have dark, smudged blotches, particularly those taken under bright sunlight and featuring large expanses of sea or sky (examples here).

The camera will probably need servicing, but right now I'm more concerned with trying to salvage my pictures. Other than painstakingly retouching each photo one by one, is there any way to batch-correct them on software? Maybe some sort of Photoshop trickery that can be pointed the location the specks, analyse them and apply some magick to compensate?

Thanks in advance!
posted by doctorpiorno to Computers & Internet (10 answers total)
Well, the patches look translucent and are in consistent areas, so that's good. I'm not a Photoshop professional, but I have been toying with it for over a decade. I would try to do the following:

Create clipping paths out of all the smudge-areas.

Manually chop the paths up into separate paths by way of brightness differences.

Figure out exactly how much brightness/contrast each separate path needs to match the rest of the photo.

Batch process the brightness/contrast shifts after you (manually) determine the amounts each needs to be shifted.

I'm not sure if it'll work as intended, but it's worth a shot. Try it on a dozen or so first.
posted by griphus at 11:16 AM on November 21, 2010

Try using the 'Dodge' tool, play around with brush sizes, exposure, and (and softness). You should be able to pretty easily remove the most obvious splotches this way.

If you don't have photoshop, Pixlr should be adequate for this case. It won't be perfect, but it should be a big improvement, and won't take much time at all.

I'm sure there are better methods of photoshop trickery for fixing this, but those seem like the most obvious ways of doing a quick fix.
posted by schmod at 11:19 AM on November 21, 2010

You need the Photoshop tool that's called the Healing brush. Basically, it is designed for this kind of scenario.

Here's a video detailing all relevant tools in Photoshop.
posted by fake at 11:20 AM on November 21, 2010

Yeah the healing and clone tools should at least help you with the sky. Water is a little more difficult - not impossible - because you'll create a blur around the edges. But if you save a re-named version of your pic, you can go wild and learn how to refine your techniques.
[also: hey I know that spot! Got some pics right here...]
posted by Namlit at 11:30 AM on November 21, 2010

I have another way to fix this problem. Do me a favor and take a picture of a brightly (like sunlight-bright) illuminated white piece of paper. The paper should fill the entire picture, so that there is nothing but white.

If you do that, we can invert the dust (which is all that will be in the picture) and add it back to the original image. That should neutralize the effect pretty well.
posted by fake at 11:35 AM on November 21, 2010 [2 favorites]

(The cool thing about Photoshop? You've gotten 5 answers so far. They're all technically correct)
posted by schmod at 11:38 AM on November 21, 2010

Wow, that's a great idea fake. But why would he add it instead of XOR it? Unless I am totally misunderstanding how XOR works.
posted by griphus at 11:38 AM on November 21, 2010

I believe Photoshop Lightroom has a built-in dust removal tool.
posted by kenliu at 12:38 PM on November 21, 2010

Wow. So many great ideas! I'm going to give fake's idea a try first to see if I can automate the process somewhat, seeing as I have quite a few pics to fix, but thanks everyone for your help. I'll keep you posted.

By the way, didn't know about Pixlr, but I'm liking it a lot so far. May end up using it a fair bit for light-duty retouching. Cheers!
posted by doctorpiorno at 1:58 PM on November 21, 2010

Wow, that's a great idea fake. But why would he add it instead of XOR it? Unless I am totally misunderstanding how XOR works.

In Photoshop, there is no subtract tool/blending mode. So you put the two layers on top of each other, with the photo on the bottom and the INVERTED dust image on the top. Choose the blending mode Linear Dodge. "Linear Dodge" is the Photoshop team's way of saying "ADD".

Since you're adding the inverse, you are subtracting. If you can find an XOR mode in Photoshop, let me know.

doc, if you have trouble with this method, let me know. I have done it before and it definitely works, but getting the right dust image can sometimes be tricky.
posted by fake at 6:32 PM on November 21, 2010

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