a2 June 2012

Tutorial: What makes HDR photo look unrealistic?

This is another version of Just walking HDR photo taken in Cabo da Roca, Portugal. This version was in fact more popular on 500px portal.
Today I would like to briefly discuss a few factors which make tone mapped photo unrealistic. I'm trying to achieve realistic HDR look with my photos and although I don't always manage to I think I now more less know how to do this. I will show samples of the issues (these won't be my 'real' photos but rather some extremes I produced to show the problems) and write a few words on how to fix this in Photomatix, Lightroom or Photoshop. For additional information read my HDR tutorial.

  • Halo artifacts: it's the most common mistake, made especially by beginners. It's about leaving halo artifacts around the edges. It's visible mostly on the boundary of two regions with very differencing brightness (eg. between sky and forest). You can fix this in many ways: decrease Strength, decrease Lighting Adjustments setting to Natural or Natural+, increase Smooth Highlights. You might also want to use combination of these to achieve halo-free results. Another fix is to use burn and dodge tools in Photoshop but I always try to fix it in Photomatix.
    Here is example of this issue created when using Surreal preset from Photomatix Pro 4.2:
  • Oversaturated photos: One of the common mistakes is that Saturation setting in Photomatix Pro is set to relatively high value. This makes colors to have this grunge or surreal look - they scream HDR! I usually don't go beyond 80 with this setting and most of the time I keep it around 40 or 50. Also you have to be aware that this slider is a bit different than Saturation in eg. Lightroom or Photoshop in a sense that other settings affect its behaviour, eg. using lower value for Strength allows you to use higher values for Saturation. Using higher values for Strength in turn requires reducing Saturation to keep the realistic look.
    Another thing is that particular colors (especially reds and greens) might still look oversaturated despite using rather low Saturation value in Photomatix. The fix is easy. You can use Finishing Touch in Photomatix or Saturation sliders in Lightroom (or Hue/Saturation Adjustment Layer in Photoshop CS) to decrease saturation of these particular colors. Another fix is to use Vibrancy slider in Lightroom.
    Here is example photo. The blues in the sky and reds of the tram are very unnatural in this case.
  • Unrealistic shadows: Another common mistake is to restore all detail in shadows in case of very contrasty scenes (eg. sunsets). Normally our eyes don't see all the detail in the shadows and highlights. So when we look at the photo with all details restored we perceive it as fake. The solution is to make shadows a bit darker. You can play with the Luminosity setting or fix the brightness in post eg. using curves tool in Photoshop.
  • Leaving ghosts not fixed: Many photographers leave ghosts in their images. Ghosts are subjects which moved between photos of a bracketed sequence. They can be people, cars, water or blades of grass. Sometimes photographers leave them by accident (because ghosts are relatively small and hard to notice), sometimes they don't know how to fix them or the software they use doesn't do this well. One of the most interesting cases, however, is when photographer fixes the ghost but forgets to fix its shadow or reflection :)
    Photo posted above has one more issue. Zoom in and see what happened to people and also car. They are semi-transparent and also there are several copies of each of them - hence the name - ghosts:
  • Sky looking as copied from another image: this is another common mistake making sky look as if it is copied from another image. It's often because Lighting Adjustment setting wasn't set correctly. Another fix is to increase Smooth Highlights setting.
    Take a look at this example:
  • Incorrect White Balance setting: setting white balance to correct value is always important. When you don't do this prior to merging your photos to HDR you might get unpleasant and unrealistic look (either too cold or too warm depending on your settings). You should always fix white balance prior to merging photos to HDR. But in case you can't do this you can increase/decrease Temperature in Photomatix or play with Color Balance or Hue/Saturation adjustment layers in Photoshop.
    Here is example of this issue (note the blue color of the shadows):

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