What Is HDR? A Quick Overview
HDR stands for High Dynamic Range. The idea is simple: the human eye can see much more variation, or range, in the lights and darks of a scene at one given time than the sensor in a camera. Thus, what we see with our eyes as a complete, high contrast scene can come out of the camera looking “blown out” in the highlights or “murky” in the shadows, in either case resulting in a loss of detail that, as you can see with your eye, is truly there! The problem has frustrated photographers since the beginning of photography itself, and until the advent of the HDR process, the camera operator often had to make a choice between exposing for the highlights or shadows. Most of you probably know that picture you took of your friend on the beach with a great sunset behind them, but try as you might you could either have their face exposed and the sky blown out, or a great sunset with your friend showing up as a black silhouette. As Trey Ratcliff puts it, the HDR process is a way to create images that more accurately reflect what we remember from the scene, in effect allowing both your friend and the sunset to be accurately exposed in the photograph. The process allows a large amount of creative freedom, however, and the results can range from hyperreal to completely surreal and crazy. You will see shots of both types on our blog.
At some point we will post a full-length, very detailed HDR tutorial that will go into the nuts and bolts of the process but, for purposes of this overview, I’ll cut to the chase with an example.
It starts with 3 identical, “bracketed” images, taken from a tripod. One is “too dark” with good tone in the highlights, one “blown out” and exposed for the shadows, and one in the middle that doesn’t look good on either end of the dynamic range scale.
The aperture (f-stop), focal length, and ISO are all the same for each of the 3 shots. The variable here is the shutter speed, controlling how long the exposure time is. The darkest image has the shortest exposure, the brightest one the longest. You can see the neutral exposure, the one that the camera would have taken had I not been bracketing, exposes poorly for both highlights AND shadows, making this scene ideal for some High Dynamic Range processing; the camera simply could not deal with that amount of range between the brightest white and the darkest black.
These 3 images are then taken into the HDR software, Photomatix Pro (again, more on this process will be posted once we are finished with the tutorial) and buttons are pressed, sliders are tweaked, and the computer does its complicated math. The result is a 32-bit image that must be “tone-mapped” in Photomatix, where you are able to make choices like how much blending you want between the 3 exposures, how much saturation should there be in the highlight and shadow areas, and more. Once that’s done, you get something like this:
The above image, however, is not done yet! You can see a huge improvement already; there is detail now in every part of the image. You can see that the great foreground details in the “light” exposure have been merged with the awesome cloud definition in the “dark” exposure, and the middle one provides detail in the boats and ocean. Many people who do HDR work will stop here, and call it a day. You could easily do that, as Photomatix does the bulk of what makes HDR so great. For me personally though, at this point there is still one more step, and its the fun part: Photoshop! Adobe’s wonderful “digital darkroom” is the final stop for all my HDRs, where I usually end up making a couple layers with layer modes, doing a lot of masking, dodging and burning, selective saturation bumps (and occasional desaturation) and lens correction (removal of vignetting, the darkness in the corners, correcting for distortion). The final step is to decide whether to crop, and if so where I want to crop. In this case I chose to emphasize the wonderful sunset and dramatic clouds by cropping a bit off the bottom, making the image closer to the “rule of thirds” that you hear about so much in photography. It’s not exactly 1/3 foreground and 2/3 sky, but its good enough for me.
Anyway, I hope that overview at least gets you started and helps to explain what it is we are doing in our images. For a full-length, detailed tutorial I still recommend Trey Ratcliff’s over at Stuckincustoms until we can get our own together, but who knows when that will be. For now, thanks for stopping by and enjoy the rest of our site!
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