Image Blending in Lightroom with Enfuse
- January 4th, 2010
- Posted in After Dark . Camera . Lightroom . Photography . Technique
- By gudstrand
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The Minneapolis skyline after dark can be spectacular. In the picture above the skyline and its vibrant colors are reflected on the mirror-like finish of Lake Calhoun.
Before we can start a discussion about HDR (High Dynamic Range), we first need to begin with an understanding of what dynamic range means. In photography dynamic range is the ratio between the minimum (shadows) and the maximum (highlights) light intensities in an image. This ratio is measured in f-stops when referring to digital cameras.
I will leave it to the experts to debate how f-stops of dynamic range the various formats and cameras can attain. Even if you use the very best DSLR it is still likely that you will on occasion (often?) find photo opportunities that will exceed the dynamic range of the camera. This is where HDR and/or blending techniques come in.
For those looking for more information about dynamic range you can find a great reference here.
HDR or High Dynamic Range
HDR has become a very popular technique due in large part to a number of very good tools that have become available. Photomatix is probably the most well known and popular, and while it does a good job, it can be very difficult to get decent results. Most HDR that I have seen ends up looking kind of unreal and/or like a cartoon. Some people like this, but it is not for me.
The trick, I think, is to use the tools to accomplish a subtle effect and to not go overboard. While the goal is to present a much larger dynamic range than can be accomplished with a single shot, you should also strive for realism.
While Photomatix and similar tools use tone mapping and exposure fusion, there is another technique that can be used which is image blending. One of the tools that can be used for blending is Enfuse.
Enfuse is an open source tool which can be downloaded for free. The Wiki page does a much better job of describing it:
Enfuse is a command-line program used to merge different exposures of the same scene to produce an image that looks very much like a tone mapped image (without the halos) but requires no creation of an HDR image. Therefore it is much simpler to use and allows the creation of very large multiple exposure panoramas.
Sounds like just what we want.
The downside to Enfuse is that it can be daunting to use for those less technically inclined. It is a command line tool, and if you’ve never ventured out of Windows and into the world of command prompts, it could be a show stopper. However, if you have Lightroom there is an alternative.
Timothy Armes, who has authored a number of Lightroom plug-ins, has created one just for Enfuse called LR/Enfuse. In short this plug-in allows you to simply select the images that you would like to blend within Lightroom.
Accessing the plug-in
Once you have the images selected the next step is to start the plug-in. The Enfuse plug-in is a bit different from most, to launch the Enfuse process select File->Plug-In Extra’s->Blend Exposures using LR/Enfuse.
When the plug-in is launched you are presented a window that contains four tabs that configure and control the output. It may seem like a lot but the settings for the most part do not change all that much between sessions and the actual blending options are limited to one tab (Enfuse)
The output tab is where you specify the name and location of the output file. I almost always output to the 16 bit TIFF format. You can also opt to import the output file back into Lightroom, copy meta data to the blended image, etc.. You can see my typical settings below.
Auto Align Tab
The auto-align configuration determines how (or if) the images should be aligned during the blend. Even shooting on a tripod I find that I do need to have the plug-in automatically align the images. Even the slightest shift of the source material can lead to a blurry image, auto-aligning can correct for that.
This tab is the one place where you are able to tweak the blending. I leave the levels set to automatic and if you are just starting out you should too.
The other parameters control the weighting factors used by Enfuse to blend the images. Input images are weighted according to their exposure, contrast and saturation. Changing these values will effect the blend and how the pixels are blended. The contrast weighting is the only one of the values that is not determined on a per pixel basis. Instead it looks at a window of values whose size is determined by the Contrast Window Size.
Al the bottom of all the panels is a generate previews button, I would recommend that you leave the auto generate unchecked and instead manually create a preview when you are done with you r changes.
The configuration tab typically needs to be set up only once. The only config here that is interesting is the preview pixel size. The larger the size the longer it takes to generate the preview. The default is 500 which is too small for my taste, 800 seems about right.
Shooting to blend
When shooting HDR, you typically will need 3-5 images which are bracketed at equal stops. The beauty of blending is that you can be much more liberal with your source material. The documentation for Enfuse recommends starting out with pictures bracketed by 2/3 to 1 1/3 stops to make it easier to visualize. Typically you want to get a “base” exposure that is as close to the look you like and bracket from there. If you are concerned about the shadows, bracket up and don’t worry about bracketing on the –EV side for highlights. Blending is very forgiving and is not dependent on a certain mix of photos.
Also, to make your life easier, you will want to use a tripod. Some of the various blending and/or tone mapping products will handle slight movements of the camera, but from my experience it is just best to start with images that are framed as identically as possible.
For the image I present here I shot three exposures. As I said earlier I am not a huge fan of the really overdone HDR in most cases. For some source material it works pretty well (see my article on Topaz adjust for one that I think puts the effect to good use. IMHO :-)) but for this scene I definitely wanted something with more realism. Blending is just the tool.
Below are the three images that were blended to create the photo at the beginning of this article. As you can see each image captures detail in some areas but not in all. By blending the three images, we are able to get a final result that combines the areas from each photo to ultimately deliver an image that exceeds the dynamic range of a single frame.
Exposure at –2 EV
In this image you can see the details in the city lights and in the reflections on the water. The buildings themselves are obscured by the shadows and the tree line is nothing more than a silhouette.
Exposure at 0 EV
At this exposure you can see the buildings are opening up and there is detail appearing in the tree line.
Exposure at +2 EV
Now we see lots of detail in the tree line but the buildings are washed out. The city lights are mostly white blobs.
Blending images is a great way to increase the dynamic range of your photo. It also has the advantage of providing a more realistic look, and with less work than the popular tone mapping tools. As a bonus Enfuse itself is free and the plug-in for Lightroom is much cheaper than the popular tone mapping tools (think PhotoMatix).
In short if you are a landscape photographer, you owe it to yourself to try out Enfuse and blending; Heck, any photographer would benefit from having this tool in their arsenal. Download Enfuse and the plug-in and try it out. I would love to hear from you and see your results. I think you will be as excited about blending as I am.