Blame it on the nitrogen narcosis.
At least that’s the story I’m going with on this one. Because in my mind, the photos I was capturing during the dive were spectacular. I was going to win awards!! Get published in National Geographic!! Maybe even have a chance at becoming the next Steve Zissou.
And then I came back up to earth and I saw those same photos on my laptop screen -- yikes. There was backscatter everywhere:
Original photo before editing. Japanese tank on the wreck of the San Francisco Maru in Chuuk (Truk) Lagoon.
In this post I’m going to show you a useful technique using Adobe Photoshop that can save those once in a lifetime underwater shots that didn't come out exactly as planned due to heavy backscatter.
Let’s take it from the top. This was a deep dive, as are many of the wrecks in Chuuk (formerly known as Truk) Lagoon. My goal on this specific dive was to photograph the World War II era Japanese battle tanks on the deck of the San Francisco Maru cargo ship. The deck of the ship is at 165 feet (50 meters), which yields challenges from both a scuba diving and photography perspective:
- First and foremost you need to pay close attention to your depth, bottom time (you don't have much), gas consumption, and any necessary deco stop data.
- Next, due to the depth, there is very little ambient light. You are dependent on your camera strobes for lighting.
- Third, you’re diving in a lagoon. The water has a ton of stuff in it: rust from the ship as well as plankton, sand and other particles.
- And finally, you're pretty narced the entire time.
All these factors come together to create the perfect storm for an image full of backscatter.
How to Reduce Large Amounts of Backscatter
Most of the time I do all of my editing in Lightroom. The spot removal tool is perfect when you've got a few specks of backscatter to clean up. But when you've got a shot like the one above, you need to break out the big guns to save it. This means using Photoshop.
Start by getting your image into the best state that you can using the tools that Lightroom provides. Then when you're ready to tackle the backscatter, right-click on your image in Lightroom and open it in Photoshop as shown in the following screenshot:
Now you should have the image opened in Photoshop. But let's start by describing the objective before we get to the step by step instructions:
We want to reduce the backscatter that we're seeing in the blue water. Photoshop has a cool filter to remove dust and scratches from an image. That's essentially what our backscatter is. The filter works by blurring pixels near each other together. So the white flecks of backscatter will get blurred with the blue water pixels nearby, therefore reducing or eliminating the appearance of the backscatter. How much blur to apply is something we can configure when using the filter. To remove bigger specks, you need to blur more pixels.
But the problem is that when we apply this filter out of the box, it gets applied to the entire image. That means that the Japanese battle tank will also get blurred -- which is not what we want.
So what do we need to do?
The key to solving the problem is to use something in Photoshop called the history brush in order to only apply the dust and scratches filter to the parts of the image that we specify.
Lets do it.
We'll start by selecting Filter -> Noise -> Dust and Scratches as shown:
Next, select an area of the image that has a lot of backscatter. You'll see a zoomed in view of that area in the Dust and Scratches filter window:
Increase the radius setting pixel by pixel until you see the backscatter disappear. For this image, the magic number was 18, which as you can see in the screenshot below is a pretty significant blur. You can really see how blurry the tank has become, but don't worry -- we'll fix that next!
Click OK to apply the Dust and Scratches filter to the image.
Next we need to tell Photoshop that we really only want it to use the dust and scratches filter on the parts of the image that we specify. That's where the history brush comes into play.
Let's start by opening our history panel in Photoshop. From the menu, click Window -> History. This will bring up your history panel:
In order to use the history brush to selectively apply the dust and scratches filter to only the parts of the original image that we specify, we need to assign the Dust and Scratches filter action to the history brush. In the history panel, click the checkbox next to the Dust and Scratches line item.
The history panel should now appear as shown:
Now we want to go back in time to the original image state. We can easily do this using our history panel. Just click on the first line in the history panel titled Open. Your screen should look like this (notice the image is now sharp and all the backscatter is back...that's because you're looking at the image in its original state):
We're almost there!
Next, select the history brush from your tools menu. It's the icon that looks like the one outlined in red in the screenshot below:
And now its time for you to become an artist.
Use the history brush to paint the areas of the image where you wish to apply the dust and scratches filter. Make the brush bigger or smaller and zoom in on the image so you can be more precise. For example, I wanted to blur all the blue water background, but NOT the tank itself or my dive buddy Brandi.
Once I finished using the history brush in Photoshop, I saved my work and went back into Lightroom to make a few last edits with the spot removal tool.
And you can clearly see the result in the before and after images below:
Before edits in Photoshop.
After edits in Photoshop.
This technique is especially useful when you've got a lot of backscatter to deal with in the background of your image. It won't save every image, and in this example it still won't turn this shot into an award winner. But it did yield a much better result than what I captured in the camera and it makes for a nice memento from this really cool dive!