Fighting Those Nasty Dust Spots...

[Jay Beckman]

Ok, since dust spots seems to be a hot topic right now, lemme tell you how I attack the problem.

Unfortunately, aviation photographers are saddled with a double whammy of slow shutter speeds (meaning small apertures which bring dust more into focus) and our subjects are most times surrounded by feature-less sky so dust can't hide in the clutter of a landscape, buildings or the normal patterns and textures of every day shooting.

One way to help yourself before you even go shoot it so remove your lens, put your camera in manual cleaning mode, tilt the body so it faces downward and give your sensor a few squirts with a Rocket Blower (don't touch anything with it!)  Much of the larger junk will be dislodged and your post processing workload just got easier!  Even though Canon uses canned air, I strongly suggest you don't because one mis-tilt of the can and you'll blow propellant all over your sensor and that's really bad.

For those pesky spots that won't go away, I'll open an image in Lightroom and perform the bulk of my processing before attacking the dust.  The main reason is that there's a good chance the stuff around the very edges will go away with a bit of cropping.  For the spots that remain, the best way I've found to track them down is to drop my Brightness to Zero and raise the Contrast to 40 or 50.  This makes the spots stand out even more like sore thumbs and then it's pretty easy to attack them with the Dust Spot tool.

One key thing to be aware of though: If the clone tool wants to reach too far up or down on the screen for a "patch," be aware that the luminance value may not match perfectly (especially if the sky is tending to be a pretty pronounced gradient) so you'll be trading a dust spot for either a dark spot or a light spot instead.  Try to make the tool go as much horizontal as possible so that the tones will match.  The good news is that it's all relative so when you bring your Brightness back up and re-set your Contrast, the values will still match!

Also, look carefully for spots in prop arcs and in the background too.  Even though you've got some nice background blur going because you nailed the pan, dust is position-static in the frame so it can still show up even in the blurry weeds at Coolidge or the grass and far runway at Willie.

One more useful tip regarding Lightroom.  Once you've done a very, very thorough cleaning on one image, you can copy your cleanup and paste it to the entire rest of your shoot!  Now, you might end up with some clone spots where you don't want them but it's easier to go in and remove a few than have to do a bunch all over again!

Hope these tips help and Happy Snapping!

[bilwor]

Thanks Jay for a timely (for me) topic. Good info. What I have started doing before I go out on a shoot is to take a photo of only the sky at home and check for spots before I leave.

Especially places like Coolidge take your Rocket Blower with you and check for dust on the filter.

bill word

[Joe Copalman]

This topic has been due for a bump for some time, so I figured I'd add my preferred method for tackling dust spots. 

Jay mentioned his approach to dustbusting through Lightroom, what follows is the method I use through Photoshop Elements 5.

It doesn't matter if you make your expsoure/color adjustments before or after doing this, but since ACR (at least the version I have with Elements 5) doesn't include a clone-stamp tool, you will need to make any RAW edits in ACR before moving on to this step in Elements. 

If I'm dealing with an overwhelming amount of dust spots, I'll typically crop the image before I start cloning to cut down on my workload, unless I'll need to clone from an area outside of my intended crop.  The first image below is straight-out-of-camera, with the exception of the crop. 

When you're ready to tackle the dust, the first thing you'll want to do is create a duplicate layer.  To do this, go to Layer --> Duplicate Layer, then click "OK."  You can rename the layer, but you're going to delete it anyway, so I never bother.

After you have created the dup layer, you'll want to equalize the image to bring out the dust spots.  To do this, go to Filter --> Adjustments --> Equalize.

If you do this and don't see a lot of dust spots, you're in good shape.  If what you see looks like the second image below, you've got a pretty bad dust problem and have a bit of work ahead of you - IF you believe the image is worth the work.  Also, it's time for a sensor cleaning.

So, now that we can see all the dust spots, it's time to attack them.

If it's not already open, open the palette bin on the right-hand side of the screen.  Click on the image marked "background."  This is important, as the edits you are going to make are going to be to the original image, you are only using the equalized layer to identify where the spots are.  Once you have done this, you will want to select the clone stamp tool from the left-hand toolbar.  (If you haven't used it before, it's the icon that looks like a rubber stamp.  If it is set to the pattern stamp tool, just click and hold on it, and it will give the option to select the clone stamp tool).  You can adjust the size of the brush up top - you want to aim for a brush size that is slightly larger than the spots you are wanting to clone out.  The narrower the aperture you shot with, the smaller the dust spots.  After using this method a while, you'll get a feel for which brush size to use depending on how you shot the image (with shots taken at f/7.1 on a 50D, for instance, I know that a brush size of 155px or so works great).  I also tend to bring the opacity down a tad, usually at around 85% or so.  This allows me to "fade" the spot out rather than slam a 100% opacity copy of adjacent pixels on top of it.  Your mileage may vary, but I've had a bit more success in "blending" these clone stampings in with the surrounding area than I did at 100%.

To clone a spot out, you'll want to source the cloned pixels from as near the dust spot as possible, with the focus being on matching the area surrounding the dust spot.  In Jay's post, he mentioned trying to clone from an area as horizontal as possible, and this is solid advice.  That said, keep an eye out for any vignetting, especially toward the edges.  In these cases, a direct horizontal clone may not be viable.  What I've found to work here is to clone along the arc of the vignette so you're matching the "fade" as closely as you can.  But typically, you'll find a dust-spot free area next to the spot, select that as your clone source by holding ALT and clicking, then placing the brush directly over the dust spot and clicking twice.  Repeat this for as many dust spots as you have.  When you are done, right-click on the "background copy" thumbnail in the palette bin on the right-hand side of the screen and select "Delete Layer."  If you lose track of what you've cloned and what you haven't cloned, you can delete the dup layer and go through the process again starting at creating a dup layer.  This is also a good way to check your work.

The third image below was done after several cycles of the above process and shows a relatively clean image.  At this point, after deleting the dup layer I used to check my work, I saved the image as a .tiff.  If I ever need to go back and edit this photo again, I have a dust-free copy of it.  From this point, I went on and made whatever remaining edits I needed to make.

I chose an extreme example for this post to show what is possible, but it is also worth pointing out that I hardly edited any other photos from this particular trip to Coolidge, as most didn't warrant the hassle.  Proper care and regular sensor cleanings are very important, and can save you A LOT of time going through and cloning out dust spots.

There are also several ways of avoiding or minimizing the potential for dust spots, but I'll cover those in another post.

[Joe Copalman]

If anyone has another method of killing dust spots, please feel free to sound of with a brief how-to on how you do it. 

[Joe Copalman]

There are a few methods I use for preventing or limiting dust spots in my images.  These are just the methods I use, if you do something else that is effective, please post it to this thread.

-Regular cleanings.  I take mine to Tempe Camera every 3-4 months.  They currently charge $35 for a sensor cleaning, and $55 (I think) for sensor, mirror, and viewfinder cleaning.  I'll usually spring for the $55 treatment once a year.  Several AzAP members do their own cleaning, which saves them both time and money. 

-Regular maintenance.  I picked up a Giotto Rocket Blower a while back and it works fairly well at getting quite a bit of the dust off of my sensor in between full-blown cleanings.  You can pick one up for under $10 these days: http://www.amazon.com/Giottos-AA1900-Rocket-Blaster-Large/dp/B00017LSPI.  You can also just shout "HEY, DOES ANYBODY HAVE A ROCKET BLOWER I USE FOR A SEC?" at any shoot where a half-dozen or more photographers are, and chances are someone will have one.

-Shoot at higher shutter speeds and/or wider apertures.  We all love prop blur, but getting it requires long exposures, which in brighter shooting conditions, often yields apertures as narrow as f/22 or smaller.  Rule of thumb - the higher number, the more dust will be visible.  The lower the number, the less will be visible.  For a visual demonstration, go outside and take a shot of the sky on aperture priority at f/8.  Then take the same shot at f/22.  When shooting on shutter priority, the camera will select the appropriate aperture for the shutter speed and ISO you've selected.  Unless I'm shooting in low-light conditions, I'll set my camera at ISO100 to yield the widest aperture possible with whatever shutter speed I select.  Even then, when shooting at shutter speeds lower than 1/160, I'll need to bump up my exposure value by +1/3 to +1, depending on how low I go.  If I'm shooting at 1/60, more often than not, I'll have to use a full +1 of EV to open up from f/22 to f/16 or so - still not ideal, but much less dust to contend with.  Neutral-density filters are another option to help yield wider apertures at lower shutter speeds, but I have not used one, so I can't speak from experience on that.

-Frame your shots with dust-mitigation in mind.  At the last Coolidge Fly-In of the 2010-2011 season (May?), I brought my ladder out with me and hauled it all the way out there for landing shots.  My reason for doing this was because my wife had recently given birth to our second child, and my money and attention had gone to things other than staying on top of my sensor-cleaning schedule, and I knew that even at a safe 1/250 and f/10-ish, I'd be dealing with more sensor snot than I wanted to.  My objective was to get up higher to get more of the runway, trees, and horizon in my shot to 1)give me a darker background than the bright morning sky to yield a wider aperture, and 2)give me a darker background for dust spots to blend in against.  With the kind of shooting we do, the sky tends to be where dust spots show up the most.  By limiting the amount of sky in my shots from Coolidge that day, I gave myself a far lighter workload when it came to processing those shots.  I also noticed that I really liked the angle I got, so I've hauled my ladder out there again. 

That's pretty much all that comes to mind right now.  If anyone else has further tips on preventing dust spots or on removing them from images you've already taken, please post them to this thread.

[Chris Kennedy]

Joe posted a good explanation of how to clone out dust spots in Photoshop Elements. However, if you have a later version of PE you can use the Spot Healing Brush Tool for a one-step removal of the spot.

You set it on Content-Aware, set the brush size and, while holding down the left mouse button, paint over the object you want to remove, in this case the spot. As soon as you release the mouse button, the software removes the object/spot using the surrounding area to fill in the part that is removed. It's a one-step cloning process.

It does a pretty good job, particularly if the background is fairly clean. It even does a pretty good job when the background is somewhat complex. It's great for removing those cones that the FBOs like to put around parked aircraft.

Since the spots we tend to see are the ones in the sky, this tool works very well.

Following are before and after shots illustrating the removal of a ramp edge light. This shows what it can do with a fairly rough background. It works even better on spots in the sky.