A Brief HDR Tutorial
Written by: Tiffany Joyce
“HDR” stands for High Dynamic Range imaging. The definition from Wikipedia is, “a set of techniques that allow a greater dynamic range of luminances between the lightest and darkest areas of an image than standard digital imaging techniques or photographic methods. This wider dynamic range allows HDR images to more accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight.”
It seems to be one of those photography techniques that people either love, or they hate. Like any other technique, the effects of HDR can be used in a subtle way or an overt way. It can be used to give your picture a surreal look, or it can be used to add subtle dimension and contrast. It takes a bit of experimentation and uses both camera techniques and post-processing techniques. Essentially, though, it’s pretty easy to accomplish and modify to suit your own personal needs and tastes.
To achieve the effects of HDR, you will need to shoot in RAW file format.
First, choose your subject and put your camera on a tripod. You’re going to take a series of photographs that need to be composed exactly the same, but will be shot at different exposures. Take the first picture at “normal” exposure, noting the aperture and shutter speed. You’re going to use the exact same aperture for the subsequent shots, but will increase and decrease the shutter speed to over- and under-expose them. This is called “exposure bracketing”, when you “bracket” the normally exposed photograph with one (or more) that is under-exposed and one (or more) that is over-exposed.
Also, be sure to shoot in a low ISO setting to reduce the noise as much as possible, because noise translates very obviously into the final product. I broke that particular rule in the following shots, where I was shooting in the dark outside of my house, at 7:30 at night, using ISO 800. But for the purposes of this short tutorial, I’m sure you get the idea. Ideally I would have taken these photos at ISO 100.
Here is the “normally” exposed shot, 10 seconds at f/13:
Here is the “underexposed” shot, 5 seconds at f/13:
And here is the “overexposed shot, 20 seconds at f/13:
What you’re trying to do is bracket the normally exposed photo with one that is shot at one or two stops up, and one that is shot at one or two stops down. We talked about stops in this entry.
Now we’re going to merge all three photos together. Open all three photographs in Photoshop CS2, CS3, CS4, or Lightroom. Other photo editing software programs will have similar steps to what I describe here.
Go to the “File” menu and choose “Automate”, then “Merge to HDR”. When the “Source Files” screen opens, click the button that says “Add Open Files”. Then click “OK”. Click “OK” again when the program asks you if you want to merge the files to HDR. The next screen offers you a “preview” of the finished file. The files you used to compose the HDR photo are listed to the left, and you can de-select any of the files to remove them from the merge and change the appearance of the final file. You also have the opportunity to adjust the “White Point” by using the white point slider to the right. Moving the slider to the left lightens the appearance, moving it to the right darkens the appearance. The screen opens at a middle setting; for my final shot I set it two-thirds of the way to the right.
Finally, before you click “OK” you’ll want to change the image from 32/bit channel to 8/bit channel, so that you can save the file in JPEG format. If you don’t change it at this point, you can also change the photo’s mode by going to the “Image” menu and selecting “Mode”. If prompted to adjust the “Exposure” and “Gamma”, just leave them at the default setting and click “OK”.
This is the final, merged HDR photo:
As you can see, more detail can be observed in this picture, than what was available in any of the first three pictures that comprised the final HDR photo. The silhouettes of the trees in the back yard are visible, as is a smattering of stars up in the top left hand corner. You can also see how noise really effects the final outcome, so be sure to bump that ISO down!
Personal opinions about the use of the HDR technique aside, you can probably see how this technique would be useful in a variety of circumstances. If you experiement with this technique, we’d love to hear about it! Please feel free to share your experiences and photos in the comments.
Photo credits (all): Tiffany Joyce.
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