Understanding High Dynamic Range Photography
There seems to be a lot of hoo-haa around these days about this new-fangled technique called High Dynamic Range photography, or HDR for short. If you have been browsing the web you will no doubt have come across many differing opinions on the subject. So what is it and how do we do it?
Basically, when you take a photograph with your camera on a set exposure, there will be a certain latitude, or range of luminance, that the sensor in the camera will be able to pick up and record. Much the same as our own eyes. Anything above or below this range will be seen in the image as a blown-out highlight or a super black area that has no detail. While it is possible to tweak these parameters in your image-editing software, there can be a certain amount of image degradation if you force the shadows to lighten, for example.
A HDR photograph, on the other hand, is one that incorporates a much higher range of luminance values. This results in images that have equally well exposed highlights, mid tones and shadows, without compromising on quality.
So how do we take HDR photos? Well there are 3 methods that I know of that can be used with varying degrees of success.
1. Separate Images
This is the original and, some might say, best method of creating a good HDR photo. As a HDR image is comprised of a much higher latitude of luminance than our camera can capture in a single image, the trick is to take multiple shots of the same subject with the camera set at different exposure settings. Although it is entirely possible to take loads of shots at every conceivable exposure, usually 4 to 6 shots will suffice to get the desired effect.
A tripod is essential here as each shot needs to be frames exactly the same – so unfortunately this method isn’t adapted for moving subjects.
Try taking a landscape photo at -2 exposure settings, then -1, 0, +1 and +2. You need to have a software package that is designed for creating HDR images from these. A couple of well-tried and tested ones include Photomatrix and Adobe Photoshop CS4 & 5. Although there are other more affordable options available after a few moments Googling. I’m using CS5 for this article.
So after you import, run your program (in CS5, it’s under “File” > “Automate” > “Merge to HDR Pro”) and the software will look at the 5 different images, combining the luminance values of each into one master image that has good detail in every tonal range.
2. The RAW Trick
The second method I have been experimenting with negates the need for taking separate shots, and also a tripod, which can be really handy when you are caught without one. For this method you will need to shoot in RAW.
Open up the resulting RAW file in your editor and make sure that the “Exposure” slider is set to “0”. Save this as a separate image – the highest quality you can, such as PSD or TIFF. Now change the exposure to -1 and save again. Repeat this for the values -2, then +1 and +2 and you will have 5 “shots” of the same subject at 2 stops either side of the 0 exposure.
You can then import these images into your image editing program and follow the same steps as the first method described above. I am still experimenting with this, but it seems that I have around 2 stops of exposure “allowance”, if you will, with my RAW files before the image starts to fall apart. It’s worth playing around with this, especially as you can use this method on your existing RAW files that you perhaps didn’t shoot with the sole purpose of converting into HDR images. For images like the one below, I like ot use this method to a subltle effect that brings out the tones of both skin colors, whilst retaining detail in the highlights and shadow areas.
HDR Pro in Photoshop does a good job of combining multiple images together
3. HDR Toning in Photoshop
If you have a copy of the latest version of Adobe Photoshop, then there is an even simpler technique you can try to get that HDR effect, and it doesn’t involve multiple shots at all.
After you have imported your single image, go to the menu and choose “Image” > “Adjustments” > “HDR Toning” and let it do it’s thing.
Yes, ok, it’s not a “true” HDR photo in that sense as the software is using the limited luminance values captured by the camera at the time, but to be fair it can produce some pretty good results. You also get presented with an in-depth dialogue box where you can tinker with the parameters of the effect to make it to your liking.
This shot was taken with my compact camera; actually is’s 3 separate photos I stitched together to create a panorama, then applied the HDR toning effect to it. As you can see, it came out pretty well and I actually sold a few copies of this online.
Beware though – the slider-happy Photoshoppers amongst us can get carried away with HDR and there are some I have come across on the Web that demand a sharp intake of breath. Less is more! Unless you are going for an artistic, comic book effect, be careful and remember that some photos just do not lend themselves to creating a good HDR photograph.