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Table of Contents

Appendices

EXPOSURE FUSION – ALTERNATIVE TO HDR

INTRODUCTION

Exposure fusion in Photomatix Pro
A long time ago when no one had heard about HDR photography yet, photographers were still able to increase the dynamic range of their photos. What they did, and many photographers still do, was to open several photos in Photoshop, each differently exposed, and blend them using layer masks. When they blended the layers they had to decide which photo to use for each region of the output image. This way they could restore highlights using an underexposed photo and details in shadows using an overexposed one. So the concept is quite similar to HDR.

Although very old this technique got quite popular recently and nowadays is commonly referred to as manual blending or XDR for extended dynamic range (compared to high dynamic range).

Exposure Fusion is based on that experience but it is a more automatic process. Instead of doing it manually you can blend your images directly in software like Photomatix Pro or Enfuse. Basically Exposure Fusion is about taking the best pixels from all photos and outputting them to the final image. Whether a pixel can be considered good or bad depends on many factors like for instance colour saturation, well-exposedeness, low noise-level etc. Also exposure fusion isn’t limited to simple read and write operations. For any pixel it can take data from 1 image or from all images and to calculate the mean of values read (or some other characteristic). It can also increase colour saturation and much more. The possibilities are virtually endless so similarly as with tone-mapping there are numerous ways to do exposure fusion.

Unfortunately not many HDR software offer exposure fusion. Photomatix (both Pro and Essentials) and Enfuse are the most popular ones with such functionality built-in. As in this tutorial I’m using Photomatix Pro, I will focus on it in this section as well.

PROS AND CONS OF EXPOSURE FUSION

Before jumping into details on processing using Exposure Fusion, here are some of the benefits of using it:

  • Exposure fusion might result in noise reduction (contrary to local tone-mapping which amplifies noise) – this makes it perfect for night and long-exposure “HDR” photos where noise is typically a problem,
  • Images have very natural look. Especially real-estate, landscape and night and foggy shots benefit from this natural look.
  • Images are free of halo artifacts,
  • Using exposure fusion might be easier because it has fewer parameters to set – also it is more intuitive as many photographers are already familiar with notion of blending images, while idea of 32-bit image and it’s tone-mapping might seem abstract to some photographers.

And here are drawbacks of Exposure Fusion:

  • Images lack local contrast compared to tone-mapped images. However, this can normally be improved in post-processing,
  • High memory usage that increases with bit-depth and number of images, so often more RAM is required.

As you can see from above, exposure fusion produces images that don’t have problems typical for HDR photography: noise, halos and unnatural look. Sounds great, doesn’t it? Well, that’s one of the reasons exposure fusion became so popular amongst real-estate photographers. That’s also the reason why I use it for the majority of my night photos.

CREATING FUSED IMAGES IN PHOTOMATIX PRO

Workflow for creating fused images in Photomatix Pro doesn’t differ much from regular tone-mapping workflow. The main difference is step 1 below:

1) Make sure to use a dedicated RAW converter to convert images to JPG/TIFF prior to loading them into Photomatix Pro. This way you will achieve best quality. The reason for this is that the RAW converter built into Photomatix is quite simple – although usually it’s sufficient for tone-mapping it doesn’t produce as good results when used together with exposure fusion. For this reason I always develop my images in Lightroom or Capture One and then export them to Photomatix using Lightroom plug-in (which comes with your copy of Photomatix Pro).

2) You start by selecting photos to fuse in Lightroom (or loading them using Load Bracketed Photos dialog). Right-click them and select Export -> Photomatix Pro.

3) Then you need to specify Preprocessing Options as normally, below are settings selected by me:

For this example I shot the photos with a tripod (7 exposures at 1 EV spacing). There could still be some small horizontal and vertical movement so I checked Align images checkbox. Also there were some people moving in the frame so I checked Show options to remove ghosts option (I will skip deghosting step this time though; if you need to read about it, go to ghosts removal section in this tutorial).

4) In Preview mode switch Process to Exposure Fusion this time:

Exposure fusion settings
5) Just below Process, there is a method combo-box. You have following choices (for this example I’ll pick Fusion/Natural):
  • Fusion/Natural – it, and Fusion/Real-Estate, produces the most natural-looking results (hence the name). I will focus on this method in this tutorial,
  • Fusion/Real-Estate – this method works best for interior photos (real-estate like) but in my experience it works very well for landscape photography as well if you want very natural looking images.
  • Fusion/Intensive,
  • Fusion/Auto – fuses images automatically, you can’t control the process at all,
  • Fusion/Average – averages the images. Same as above – you have no influence on the look of the images,
  • Fusion/2 images – let’s you select two images of all your exposures and then fuses only them,
6) Specify parameters. For Fusion/Natural they are:
  • Strength – strength of local contrast enhancements. I usually leave it at 0.0 or move it to the left (negative values) as it tends to produce more natural looking images
  • Brightness – brightness of the fused image. Move the slider to the right to brighten your image and to the left to darken it.
  • Shadows Contrast – brightens the shadows. I usually move this value to 10.0 which is maximum for this setting. This way I can restore more details in shadows.
  • Local Contrast – increases sharpness and local contrast of details in the image. I mentioned that Exposure Fusion does have worse local contrast than tone-mapping – this setting tries to overcome this. I try to keep this value in range 0.0 to 3.0. Larger values might result in a painterly and unnatural look. Value of 2.0 usually works best.
  • White Clip – clips the highlights. Usually I leave it at 0.0.
  • Black Clip – clips the shadows. Usually I leave it at 0.0.
  • Midtone – specifies brightness of midtones. I usually move it to the right in order to brighten midtones to the degree that depends strictly on the image
  • Color Saturation – increases or decreases saturation of colors in the image. I usually keep it at 0 as I play with colour later in Photoshop or Lightroom. Moving this slider to the right results in more saturated images, while moving it to the left decreases saturation.

For my image I used settings from the image above.

7) Hit Apply button and save your image.

8) At this stage your photo might look like this:

Example of using exposure fusion

It looks natural, that’s for sure. However, it lacks contrast and colours a little bit (especially compared to the tone-mapped images).

So what I typically do at this stage is to open my photos back in Lightroom or Photoshop and apply some adjustments there. Most of the time I increase contrast, colour saturation and sharpen my images. After that I end up with a photo like the one at the beginning of this section.

Read about advanced HDR techniques on next page…

Read introduction to Photomatix Pro on previous page…