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High Dynamic Range Imaging – HDR or HRDI

In image processing, computer graphics and photography, high dynamic range imaging (HDRI) is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows.

The process is not very complicated for a beginner to learn provided you have some basic computing skills and a good knowledge of photography terms. You will need some equipment to ensure you get a good result.

EQUIPMENT:

  • A digital camera that allows exposure adjustments, preferably a digital camera that can bracket and take multiple shots (AEB).
  • A Good sturdy tripod.

THE CLASSIC 3 SHOT METHOD

Check your camera manual for exposure control or compensation, “manual” mode and bracketing,

Camera supports Bracketing (AEB):
Setup the Bracketing so the camera will take 3 shots with under and over exposure settings between 1-2 f-stops. Some cameras will shoot all 3 pictures in a row with one shutter button press, others require one press per exposure. Take 3 test shots and check via playback. Of your test shots, one will be normal, one will be darker (under exposed) and one will be lighter (over exposed), If you camera has information about each shot it may give you an exposure compensation value for each picture, i.e. 0, +1, -1 for each shot.

If all the shots look the same check your bracketing settings or try a higher f-stop difference for under and over exposure.

An important note to be made here is most cameras if placed into timer mode will take all 3 pictures one after the other automatically, even if they only take one at a time with the shutter button, if your camera supports it, use it.

Camera only supports Exposure compensation or Manual Mode:

If you camera only supports exposure compensation or manual mode you will need to make the changes manually for each photo, this will be difficult as you should not move the camera between each photo.

First take a shot with the exposure correct, then adjust either the shutter speed in manual mode or exposue compensation so the picture is going to be under exposed, take the shot, then do the same but for over exposure. Of your test shots, one will be normal, one will be darker (under exposed) and one will be lighter (over exposed), If you camera has information about each shot it may give you an exposure compensation value for each picture, i.e. 0, +1, -1 for each shot.

TAKING THE SHOT.

Setup your camera on the tripod and frame the shot, using the techniques above take the 3 pictures. I recommend you play around with the under and over exposure values from between .5 to 2 f-stops. This will fill your flash card quickly, but it’s worth it. If the scene has very high contract you can ‘try’ larger values. i.e. -6,0,+3.

If you have to manually change the camera settings between each shot I recommend you be very careful to avoid camera movement. and to also do it as quickly as possible.

If your camera supports RAW mode, use it, again it will fill your card quicker, but it’s worth it, particularly if your cameras sensor is better than 8 bits per color.

If your shot would require a filter as a normal single shot like a polarizing filter or Neutral density filter, use it, as this will help to avoid fringing in the final shot.

THINGS TO AVOID:

  • Moving the camera between shots.
  • Fast moving objects.
  • Long periods between each shot.
  • Long exposures with moving objects, can cause unwanted effects in final image.
  • Extreme high contrast shots without filters, fringing does not work well with this technique.

Now with all your pictures, its to the computer.

PHOTOMATIX PRO 3.0+ (software) http://www.hdrsoft.com/ :

There are quite a few application that can convert the 3 images into one HDR image, however I have found photomatix to be the simplest for a good result.

  • Open Photomatix, and select the ‘Generate HDR image’ from the workflow shortcuts.
  • Add the 3 images taken above, if you have taken multiple ‘sets’, ensure they are from the same ‘set’.
  • From the HDR view panel click ‘Tone Mapping’.
  • Make adjustments in the ‘Tone mapping settings’ panel, some recommendations that work well:
    Strength: 70.
    Color Saturation: 70.
    Light Smoothing: Mid to High.
  • Once you have the desired image, click Process.
  • Save your image form the ‘File’ menu. JPG and 16-bit TIFF is supported.

You should now have a HDR image. 🙂

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