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Thursday, April 7, 2011

How to Get Rid of Ghosting...and not the kind that say 'Boo'

How corny are my blog titles? I think they're kind of cute, but that's just me. I often find myself to be the only one laughing at things I say. Oh well. So, as promised, I'm going to give some relatively simple tips on getting rid of ghosting when processing HDR photographs. Before i do that, I want to give a shout out to Trey Ratcliff, who happens to be the Master of HDR photography. I'm sure that if you are interested in HDR photography and you're reading my blog, then you certainly know who Trey Ratcliff is. Almost everything I know about HDR photography I've learned from Trey. In fact, Trey was the inspiration behind my learning how to create HDR photography for 2 reasons. First, because his work is incredibly gorgeous and, well, who wouldn't be inspired by that level of creativity. Second, because he was an ordinary person like you and i who created a new generation in photography and became an HDR celebrity all without even trying. He convinced me that I could actually do this if I put some time into learning it. His only interest was to create photography that felt right to him and to share his secrets behind doing so with anyone who was interested in learning. Trey has a free and very comprehensive HDR tutorial on his website at stuckincustoms.com. He also has lots of great videos on his website that show him at work. Although I've never met Trey, I have a lot of respect for him as an artist and as a person, a sentiment that I'm sure all of his fans share.

So, on with my ghosting tips. There are essentially 2 ways to get around ghosting problems. The first way involves tonemapping a single RAW file instead of using multiple exposures. Obviously, if you're using only one photograph, there will be no ghosting. However, this has it's pros and cons. Sometimes, single file tonemapping works just fine and there is very little difference between a single file tonemapped image and a multiple exposure tonemapped image. But, other times, there is a huge difference. Rule of thumb...the less contrast in a scene, the more likely you can use single image tone mapping. Capturing the full range of light without clipping the highlights or shadows is vital to the success of single image tone mapping.

The second way to resolve ghosting issues, particularly with high contrast scenes, is lots of work in Photoshop. :) Let's assume we are working with an HDR image of a crowd of people in a park. First, tone map your image using the multiple exposures you took of this scene. Obviously, it's going to look like a parade of ghosts due to the movement of people between frames. Don't worry about this because we're going to fix it in Photoshop. Now, open your tone mapped image as well as each of the exposures you used for tone mapping, in Photoshop. You should have each image on their own layer, with the tone mapped image on the top of the layer stack. Essentially you are going to go through all of your exposures and find the one with the clearest shot of the people. This will most likely be on the best exposed image (0 EV) or a darker exposure (-1 EV). Ideally, you want to use the brightest exposure with the clearest shot of the people, because this will allow for smoother blending into the tone mapped image. Take the exposure with the least blur among the people and move it directly below the tone mapped image. Next, add a layer mask to the tone mapped image. Now you are going to slowly and gradually mask in the people from the "unghosted" image into the tone mapped image. Set your brush opacity low. I usually start at 35%. Zoom into the area you are masking in so you can see subtle changes in tonality. Change the size of the brush as needed. Viola....you have now removed ghosted people. Any questions?? Please post your questions and i will be certain to answer. Good luck!

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