HDR Techniques
Introduction
What is a High-Dynamic Range (HDR) image?
The "dynamic range" of a scene is the contrast ratio between its brightest and darkest parts. A plate of evenly-lit mashed potatoes outside on a cloudy day is low-dynamic range. The interior of an ornate cathedral with light streaming in through its stained-glass windows is high dynamic range. In fact, any scene in which the light sources can be seen directly is high dynamic range.
A High-Dynamic Range image is an image that has a greater dynamic range than can be shown on a standard display device, or that can be captured with a standard camera with just a single exposure.
HDR images also have the important property that their pixel values are proportional to the amount of light in the world corresponding to that pixel, unlike most regular images whose pixel values are nonlinearly encoded.
HDR Images are typically generated by combining multiple normal images of the same scene taken with different intensity levels, or as the result of creating a global illumination rendering. In practice, high dynamic range pixels use floating-point numbers, capable of representing light quantities of one to a million and beyond. Low-dynamic range images usually represent pixels using eight bits per channel, with pixel values ranging as integers between 0 and 255.
Source.
Here we're going to talk about some of those techniques for creating HDR images then mapping them back to 8/16 bit for print or screen.
Preparation
I'm going to assume you shoot RAW. I'm also going to assume you shoot multiple exposures - These techniques can be used on a single RAW file processed at multiple EV levels but your mileage may vary.
Personally I use the bracketing function on my camera, expose my first frame as near to perfect as I can then shoot two others at +2ev and -2ev. It goes without saying, a tripod is essential.
Caveat: If you subject has movement (water, trees in a breeze etc) then this can have a negative affect on the final result.
I believe you'll need Photoshop CS2 or above for some of the techniques described.
Techniques
I've heard people say they don't like HDR, personally I tend to wonder if it's a specific technique they take issue with... It is possible, with any post processing technique, to take things to extremes. To them I'd say, well try some of the other methods. It may well work for you.
There are techniques I regularly use. These are by no means definitive but I will stick with the ones I employ - Notice I don't say "know". I'm learning here as much as the next person.
The techniques are: -
- Photomatrix Using Photomatrix to perform HDR generation and tone mapping.
- Photoshop Using Photoshop (Automate | Merge To HDR...) for HDR generation and tone mapping.
- Manual Manually blending layers in Photoshop
Photomatrix can easily create images which can look, arguably, unnatural as well as the dreaded halos you see so often.
Photoshop, for Photomatrix aficionados, can look a bit bland.
Manual can produce visible layering if not done with care.
Note - You could also use Photomatrix to do the HDR generation then perform the tone mapping in Photoshop. Not sure that this brings any benefits however.