Saturday, March 6, 2010

Practical HDR

What to do when the light is too extreme for one shot?
HDR, or high dynamic range, is a digital imaging technology that allows us to go beyond the limitations of our cameras and their sensors. With this technique, we can make pictures that are closer to what we actually saw with our eyes - photographs that represent the world in more realistic renditions that simply weren't possible in the past, even with film.

How HDR Works
With HDR, start by taking multiple exposures of the same scene - exposures that vary from underexposed to overexposed - then use software to combine the tonal information from that range of exposures into a single final image. This allows you to capture detail, color and tones and merge them into one image that couldn't be captured by a single exposure. By using HDR technique and software, you can bring out more detail in the shadows, midtones and highlights. Cibodas_series
First Steps
To get started with HDR, you'll need several exposures of the same scene. Each of these exposures must be framed identically or you'll have problems assembling the final image.
Here are some ideas that work well for HDR shoots:
1. Shoot at least 3 photos, each with a difference of one or more f-stops in exposure.
2. Use a sturdy tripod and lock down your camera on the scene.
3. Avoid shooting anything with movement, including wind blowing your subject around.
4. Try using the auto-exposure bracketing function (AEB) on your camera. AEB allows you to shoot at least 3 exposures in a row with a variation in exposure for each.

How Many and How Much?
In general, you can try for a minimum of a one-stop difference between exposures, then use three to five exposures for the scene. Sometimes, the result are great using 3 frames with a 1.5- to 2-stop difference in exposure, other scenes work better using 5 frames with 1-stop difference in exposure.
I wish I could give you specific information on what exposures would work in every situation, but "every situation" is different and will require you to modify your approach. However, with experience, you'll start to know what seems to work best for the specific subjects that you like to photograph.

Into The Computer
Once you've captured your scene with multiple exposures, you need to upload them onto the computer and work on them with software that allows you to combine the pictures into a final HDR image. You don't actually have to do a lot, other than open your series of exposures into the program. The software then automatically examines your exposures and puts them together into a final HDR shot.
Most of the programs also allow some adjustments as to how the exposures come together. Sometimes these adjusments can be done before you do the HDR conversion and almost always can be done afterward. A number of software programs allow you to do this. 
Adobe Photoshop CS versions have an HDR capability. And the picture below show you what I did with Photoshop to create an HDR image from 3 bracketed images.image

And this is the result:image Other softwares you can use to create  HDR images are Essential HDR, LR/Enfuse (it's a Lightroom plug-in), and Photomatix.

HDR Processing On Other Images
Another way of using many HDR programs is to double-process RAW files. Take a single RAW image and process it twice, first to optimize the highlights (while ignoring what happens to the shadows) and again to optimize the dark areas (whike ignoring what happens to the highlights). You can even triple-process an image, creating a third version that optimizes midtones only.
Then put those processed RAW files together into a single file by using one of the HDR programs.
HDR is changing the way we photograph, giving us new opportunities for capturing the world. We now can create images that more closely render our world and more truthfully communicate what we see.
Written by Rob Sheppard, as appeared on Digital Photo Mag. June/July/August 2009. You can see more of his works at his website,
http://www.robsheppardphoto.com.

3 comments:

  1. Useful information for newbie HDR like me...still learning HDR..still get the halo effect on my HDR photo

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