Using Adobe Photoshop to Remove Backscatter in Underwater Pictures
This little blog is a response to a question on our Facebook Q and A group asking for details on how to remove backscatter from pictures using the ‘history brush’ technique. Here’s a step by step description beginning after you have opened your image with Adobe Photoshop either directly or by choosing the Edit in Adobe Photoshop option in the Photo menu of Adobe Lightroom Classic.
Once your image is open you will want to have the History panel visible.
Photoshop history panel.
If you can’t see something like the other picture in part of your Photoshop window you’ll need to select History from the list of options in the Window menu.
Next you need to apply the Dust and Scratches filter. To do that go to the Filter menu and scroll down to Noise and choose Dust and Scratches for the sub-menu.
The Filter Menu with Dust and Scratches highlighted in the Noise sub menu.
When you select Dust and Scratches you will get a window with a close up of part of your image and two sliders for the Radius and Threshold. You can select an area of image to have in the tool window and zoom in or out on it. You can also opt to preview the effect on the whole image by using the Preview tick box.
Dust and Scratches Tool
The Radius and Threshold values will be at the levels they were last time you used them or the default if it’s your first time. The text book technique for using the tool is to move the Radius slider so the spots you want to remove disappear. Then move the Threshold slider up from 0 until the spots reappear then back down until they have just gone. This will leave as much detail as possible without the spots.
But with the History Brush technique you can be more heavy handed if the areas in your image don’t have detail in them.
Once you have reached a setting that removes the backscatter click OK.
This was the setting I used to remove the backscatter in part of one of my images.
Section of an image with some backscatter and debris
After filter has been applied
Detail area of the same image before filter applied
After Filter is applied that detail is lost.
This is where things get slightly strange. You’ll see as a above that the backscatter has gone but so has a lot of the detail in the picture.
We’re now going to go back in time.
In the History panel click on the word Open. You’ll see the image go back to how it was before the Dust and Scratches filter was applied.
Then click on the small box next to the clipboard symbol and the words Dust & Scratches in the History panel.
The History Brush symbol will appear in that little box. It’s a brush with a arrow going behind it.
This is what you should now have in the History panel.
Now you can select the History Brush from the tools on the left hand side of Photoshop.
History brush selected in tools
Adjust the size of brush to suit the area you are working on and zoom in if you need to. Then you just brush away the backscatter by clicking and dragging the brush over the effected areas. You will see detail being lost so this technique is only for areas that are plain and/or out of focus so loss of detail isn’t an issue.
Be aware it’s best to use this technique first before you do any other adjustments in Photoshop otherwise it’s possible you will remove those other adjustments if you brush over them.
Here’s a section of the image with backscatter in
Here it is removed
Here’s the complete image. One of many pics of the very photogenic common sea urchins in Loch Inchard which I took during this year’s Kinlochbervie workshop.
Hopefully this has been helpful to you.
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