The Problem of Deghosting in Photomatix

Last month a promising young photographer emailed me with a problem he had while deghosting his brackets in Photomatix.

“Hey Jimmy, I need some help with regards to Photomatix and processing some shots I got yesterday, hopefully you can help! A couple bracket sequences I shot yesterday seem to majorly overexpose in Photomatix after ‘de-ghosting’, im not sure why but a large part of the sky just turns bright white after de-ghosting? It’s hard to explain but if that makes sense can you give me any pointers? I can send you the shots if you want to play around with them yourself.”

Here is is his HDR and the original exposures:

3 of the Original images

Essentially the photographer was running the auto deghosting function on his images.

In an attempt to help him, I quickly ran his brackets through photomatix. Here’s the resultant image:

Once he agreed that this was the result he was looking for, I replied with my suspicions of the cause of the problem:

“The problem is the deghosting in photomatix. Firstly, this image is fine. You shouldn’t need to deghost anything since there aren’t any moving objects, and when you do deghost anything you should do it manually.

Basically, when Photomatix deghosts an image it uses the normal exposure as its base and anything that doesn’t match up with that it strips out. So the for this image photomatix has stripped out the lower exposures in that part of the sky presumably because the clouds were moving, causing Photomatix to see them as ghosts. How do I know it’s the lower exposures?

Simply because the sky doesn’t have the lovely details that come with lower exposures. It may have also stripped out the higher exposures too but we can’t know that from this picture. It looks like the base picture was 7787 since the two skies are almost identical.

hdr courses

Remember that every time Photomatix strips out an exposure from a particular area, you lose some range of light from that area. The more range of light you lose the worse it gets, of course. That is why I almost never use the deghosting function, and if I have to, I do it manually. Very rarely will you need to for skies, unless the clouds are moving incredibly quickly. If that’s the case, simply grab the middle exposure in Lightroom or something similar and create two extra exposures so Photomatix has a bit more range to work with.

In this picture, have a look to the left of the image on the river, that is blown out as well. Again, water is a tricky one sometimes but I generally don’t deghost it.”

This problem isn’t unique to Photomatix, it’s universal across all HDR software I’ve tried. Ultimately it’s something every HDRist should be aware of – deghost at your own risk!

My name is Jimmy McIntyre and I’m the editor of HDR One magazine. I travel for a living, learn languages, take pictures, and generally strive to enjoy every minute of the waking day! You can visit my daily HDR travel blog or subscribe to my updates on facebook – Jimmy McIntyre