I often have to explain what HDR is when I mention that I have used it for a picture. In this post I hope to explain why it is important to my work, and a little about HOW to do it, but without explaining it completely. It is always good to work at something a little isn't it?
HDR stands for "High Dynamic Range", which could lead one to think, what is low dynamic range, or for you really smart folks who get to the meat of things, what the heck is dynamic range? In photography we use dynamic range to refer the relative luminance of all the part of the image captured in a photograph. From the darkest to the lightest parts. Many scenes we want to photograph have a larger luminance range than the sensor (or in the old days film) can capture. Meaning that either the bright areas are correctly exposed and the darker areas are too dark, or the darker areas are correctly exposed and the brighter areas are too bright. Many scenes have such a range of bright to dark that one single exposure will have areas that are completely black (Blocked up) and other parts that are completely white (Blown out). (This is usually the case with most of my night time temple photographs. Which was a prime driver in developing my humble skills using HDR. Specifically the program Photomatix.)
Many cameras have a setting that will allow you to see blocked up or blown out areas with a blinking warning when you view the photo on your back LCD screen after taking it. On my Pentax K5 & K200d the black areas blink green/yellow and the all white areas blink red. Which drives my wife a bit crazy, but is helpful to me.
Why does that matter? Well... human eyes are much better than the best camera sensor we can possibly build, they can manage to see hugely different levels of light in the same scene and show you detail in the shadows and not have the brighter areas be too bright. That is why when you take a photo of a scene, the photo doesn't look just like what you were looking at. Between the lens, the sensor, the screen you are looking at it on (or heaven forbid an actual paper print!) and the ambient lighting your eyes are adjusted for etc........... It doesn't look the same.
HDR is a way of combining multiple photos taken at different exposures to produce an image that when viewed on screen or as a print looks more like what you experienced when viewing the scene originally. Notice here I did not use the "R" word, "reality" is a concept I am not ready to discuss relative to photography. In part because I firmly believe that trying to capture "Reality" is a fools errand when you are a photographer!
Now, to many photographers HDR is a bad bad BAD thing, because there are so many examples of people producing results that are not... aesthetically pleasing. The software used for this type of work (I use Photomatix) has a multitude of settings, some intended for one type of scene and some for another. Misapplication of a certain pre-set can be disastrous! See the link above for some pretty bad photos.
Sometimes, on a very few occasions I have gone over the top for artistic reasons and produced a lurid image that has been popular, however, I try to NOT got there. I prefer to use a gentle touch that produces an image that looks more natural and is closer to an artistic representation of what was pleasing in an image.
Now, "how do you do it?" you ask. Easy, (Well not really but I want to to try it so I will tell you it is easy, but Shhhhhh don't tell anybody else!) I first compose the scene I want to capture. This is really the hard part, it is what separates the photographers from the plebian masses. Composition! I have read and tend to agree that the best landscape photos are taken either within 3-4 feet of the ground or way above it. That is why I am not allowed to wear nice clothing when I am on a photo expedition. If your knees are not dirty, or even better your entire torso, then you probably didn't get anything.
Once you have composed the photo, then you need to do all the other things correct, choose the best aperture for the scene, the correct base exposure, lock down the tripod etc... Then you need to either set up your camera to auto bracket exposures, or if you are like me and shooting EVERYTHING manually a lot of the time, set the bracket exposures yourself. Most quality cameras will do 5 exposures automatically and you can set the exposure gaps as you like. For something like our example below I usually choose +/- 1 stop for each photo.
This was -2 stops. (f10, 1/125s)
-1 stops. (f10, 1/60s) notice the increased detail in the shadow areas and less detail in the sky.
+/- 0 (f10, 1/30s)(or as the camera metered the scene, off the bottom right bump)
+1 stop (f10, 1/15s)
+2 stops (f10, 1/8s)
Notice that the aperture or "f stop" doesn't change. You want to keep your aperture the same, and you want to choose the correct aperture from the beginning. I usually will be anywhere from f8 to f13 depending on the lens. (Aperture determines Depth of Field or how much of the scene is in focus, as well as how much light reaches the sensor/film.)
None of these shots above looks exactly how my eye saw the scene, or how yours would either.
This, however, is more like what I remember seeing. Maybe a little enhanced, leveled and corrected for the inherent distortions of the lens, but what photographer doesn't enhance things a little though?
1) Solid positioning of the camera. HDR programs can adjust for slight movements of the camera between shots, but it can result in decreased resolution. I have shot HDR handheld in bright sunlight, but it is MUCH easier to do when you shoot a tripod.
2) The movement of elements in the shot can be a problem, called "Ghosting" for me it usually happens with cloud movement. Avoiding longer exposures, and gaps between exposures helps with that. One of the nice features of the camera automatically setting the exposures for the bracketed photos. In the linked photo I was setting them manually due to the longer exposures needed and there were up to 1 minute gaps between exposures.
3) White balance can be a huge problem if you get it wrong. HDR can magnify small differences in color and make the whole image skew off into weird color land. I will usually take several RAW images and play with them in my converter (ACR) until I like the color balance. Sometimes I have to Re-Convert ALL my shots after washing them through Photomatix and not liking the result. I prefer to work with 16-bit TIFF files in Photomatix rather than bring them in in RAW format. The converter in Photomatix tends to add noise.
4) You really should go easy on how much you use it. You can easily make an image that makes you go WOW! And everybody else barf...
5) don't limit yourself to just 3 or 4 or however many images. Some of my best images have been 6 or 7. One of my favorites was only 3, but gapped more than 1 stop apart. Longer exposures with small apertures (Larger f-stop numbers) can help you to get rid of people in a busy scene. Like this shot, if you have ever been to Temple Square in Salt Lake City at Christmas you know that it is PACKED with people. My longest exposure was something like 15 minutes which really helped to get rid of a lot of people!
Hope this whetted your appetite to try HDR! Thanks for reading!