Removing Photomatix Halo tutorial – Grey Matters
Article by Bill Fritz
Tone mapping HDR creates quite a few anomalies such as magnified image noise, ghosting, and the thing I like to call “grey matter”. What is this grey matter I speak of, where does it come from, and how can we prevent it or fix it?
This is a freshly processed HDR using Photomatix Pro. At a quick glance everything looks normal but once we zoom in and take a closer look we will find the “Grey Matter”.
Take notice to the area around the tree branch. Parts of the clouds/sky in the background are greyed out. It almost looks like an ugly halo. What causes this? This problem usually manifests on the edges between areas of high contrasting luminosities. One way I have found to prevent this from happening is to use more brackets during the tone mapping process. Unfortunately most of the time we won’t know this will be a problem until it is too late, BUT there is a way around this using Photoshop and it is very easy to do.
Step 1: Open up your Tone mapped HDR image in Photoshop.
Step 2: We also need the darkest image of the original bracketed photos you used during the tone mapping. Put this photo as a layer right above the Tone Mapped image.
Step 3: If you shot your brackets on a tripod then these two layers should already be aligned perfectly. But if you didn’t use a tripod or you want to be sure they are aligned, select both layers by holding CTRL and clicking both layers to highlight them. Then go up to Edit>Auto Align Layers. Choose the Auto Option.
Step 4: Now that everything is all lined up, the last thing to do is change the blending mode of the top layer (The dark original bracket) to “Lighten”. The “Grey Matter” areas should vanish…like magic.
Pretty cool, huh? There will most likely be a couple of things that this has done to your image in areas you didn’t want to change. For example, in my image this has caused some ghosting in the leaves. All you have to do is add a layer mask to this “lighten” layer and paint away those problem areas. This is a very quick and easy fix to a problem that we usually would ignore. Attention to detail is key, especially when it comes to HDR Photography, where anomalies are a frequent occurrence.