High dynamic range photography: a simple how-to

 

I haven’t used my film SLR camera for several years, and one of the reasons was my frequent disappointment with the limited dynamic range of the photos. Very often, details in the light or shadow areas were lost, merging into a flat white or black hole in the picture. The only remedy was to get out my camera only in low contrast conditions such as overcast weather, or just before sunrise and after sunset. Even then, the shadows or highlights would often lose detail.

With digital SLRs, it is now easy to take high dynamic range photos, provided the subject doesn’t move too much. Since I got my first digital SLR a couple of weeks back, I have experimented some with HDR and am surprised of how easy it is to get decent results.

The hdr workflow is simple:

  1. Take three or more differently exposed photos of the same scene, respectively exposed normally and for details in highlights and shadows
  2. Import them to Photomatix or Photoshop CS2 or other hdr software and output the result through tone mapping
  3. Edit in Gimp, Photoshop or other image editing software

Here are a few more details:

  1. Taking the source images
    • Since the source images are combined into one, it works better with subjects that don’t move much. Some movement within the scene is usually OK.
    • It is helpful to use a tripod, but handheld works fine as well.
    • The easiest is to set the camera to auto-bracket the exposure, keeping the aperture constant and changing only the exposure time.
    • Feel free to break the old rules and choose high-contrast images: shoot into the sunset, include a bright light in the scene, or a backlit subject.
  2. HDR processing
    • Photomatix is free for most of its functions, and about $100 for a full featured version. Photoshop CS2 also has an HDR function, but is more expensive.
    • When importing, remember that the resulting image has a tonal range far greater than what your computer screen can deal with, so it may well look awful on the screen. Don’t worry. It is supposed to.
    • Experiment with the tonal mapping to translate the raw hdr image into something that can be shown on a screen or printed on paper. Try several settings and choose the best one. Save it as a 16 bit tiff file.
  3. Final editing
    • Import the tone mapped image into your image editing software. GIMP is a good choice since it is free (open source) and does most of what Photoshop does.
    • Edit as you would any other image. Although you have a wide dynamic range in your image, don’t be locked into the idea of having to preserve all the detail in the highlights and shadows. Some images work better when the contrast is a little higher, and you have more freedom to play with this when your source image has a high dynamic range.

Here is a scene that normally has too high contrast: a wall in the shade with a bright sky in the background.

I took three handheld exposures of this Portland street scene, using the auto-bracketing feature on my camera. The first image is normally exposed, and the two following under- and over-exposed two stops. (Three exposures and two stops either direction is the maximum on my camera, which is OK but a little limited for hdr photography. Five exposures and three or four stops cover a greater range and may be needed for extremely high contrast scenes.)

img_7101.JPG
Normally exposed image with good details in the mid range.
img_7102.JPG
Underexposed image, with details in the sky and clouds.

img_7103.JPG
Overexposed image with information in the darkest shade areas.

I then imported them to Photomatix, and got this result on the screen. Moving the cursor over the image shows the area details in a separate window. (I have included two examples, one of details over the door and one in the clouds.) Photomatix automatically align the source images, and does a good job even with handheld exposures.

img-7101_2_3-screen-image.jpg
The hdr combination of the three source images, with information in the lightest and darkest areas.

And tone mapped it using the tone compressor option, and experimenting with the different settings to include as much information in the final image as possible.

img_7103_1_2_tonemapped.jpg
The tone mapped output, ready for final editing.

The colors on the tone mapped image can get a little weird (it depends on the settings you use), so for the final editing, I like to keep the normally exposed source image up on the screen as a color reference. I used level, curves, color balance and hue adjustment layers for this image, and also masks to treat the sky slightly differently from the rest of the image. The final editing in Photoshop gave this result:

img_7103_1_2_tonemapped-v1.jpg
The final image, after editing in Photoshop. I went for a vivid but still relatively realistic look.

If you have questions, I’ll be happy to answer to the best of my (very limited) ability. Just post them below.

Here are some resources I found helpful when I first explored it:

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