HDR as I understand it.

HDR (High Dynamic Range) Images are the all the buzz on nearly every internet photography forum recently. In this tutorial, I will attempt to explain from my limited yet continually expanding understanding of this technique what HDR is and how to work with it. I will not profess to know it all and the information here is not the final or even the first word on the subject. My limited background in post production photography has always relied on me getting most of the work done in the camera first before relying on post production in software programs and actions. Therefore, to keep with my personal view of photography we will look at several considerations that must be made, before capturing any image for HDR post-processing procedures. The first part would be to answer the question; what the heck is HDR?

What the heck is HDR?

While HDR is often thought of as a new subject or technique in photography, it has been an inherent part of Digital photography from the outset of the medium. In reality, the HDR phenomena has been a part of photography even in the initial analog film process. In my opinion, the most well known pioneer of photography, Ansel Adams worked with the HDR theory in nearly every image he produced. The concept he preferred to call it was known as Dynamic Range exposure.

Dynamic Range, is a measure of how many levels of light an image capture device, such as your digital camera, or film can capture. For those who are versed in the “Zone System” the translation should be elementary, as many of the concepts and techniques apply in HDR photography. For the purists out there, the question is, can I accomplish this in film photography and basically the answer would be a strong affirmative. You’re not breaking some unwritten rule of what makes photography pure photography versus photo-art.

The best example of working in Dynamic Range is to shoot a bright sunrise. Ask yourself why it is when the sun is exposed properly, the rest of the image appears dark and underexposed? The best explanation is to say that unlike our eyes the Dynamic Range at which a camera can record the image has less over all Dynamic Range than the scene being recorded. Naturally, a sunrise is a perfect high-contrast situation. The rising sun and the surrounding sky are hundreds if not thousands of times brighter, than other exposure zones in the image. While most digital sensors are extremely sophisticated, and so are film emulsions, some scenes are still too much for them to render for bright highlights, and deep shadows.

This is where the concept of an HDR image comes in. You know that if you shoot a sunrise, and meter for the sun, the rest of the scene will be overly underexposed, likewise if you meter for the rest of the scene, the sun and the sky will turn into an overexposed void of white. In some cases the range of exposre can be corrected by use of a Graduated Neutral Density filter. But for the sake of this tutorial we will bypass this option and get right to the pre and post production procedures of HDR photography. So what do you do? This is my favorite part, as this is where, “What If” comes into play.

What if you could simply bracket your image exposures, later take the properly exposed portions of each exposure of a particular scene, and seamlessly stitch them all together into one perfectly balanced exposure? You can and that’s what HDR photography is.

Post Production

There are several options for creating your HDR image in post production. In both the MAC and Windows based software systems you have a wide choice of programs you can use. One of the more popular programs is Photomatix. It allows you to merge all of your exposure together generating a 48bit image, from which you then tone map the image, or in every day English, you tweek the image to a point where the highlights and shadows are exposed properly to your tastes.

First Things First

Long before you get into the computer post processing aspect of HDR you need to have your images captured correctly. Unless you don’t breath and have a shallow pulse allowing you to shoot very steady at a high rate of speed accurately, you will need a tripod! Seriously, with a few rare exceptions you should have your camera on tripod anyways for landscape and outdoor scenic photography despite using high speed lenses with image stabilization systems. Another important element is choosing the right type of scene. You want a static scene for the best results and for the simplicity of matching numerous frames of exposure when they are shot correctly..

The most important part of creating a proper HDR image is the correct spacing of exposures. It would be easy to say that you should always bracket at a set 1.5 stops and you would have the optimal exposure range, but there are many times that will not be correct. The spacing of exposures will often vary based on the scene itself and the amount of dynamic range it presents. So I would propose you take as many different combinations as you can of a scene to become familiar with the different ranges you might encounter.

Other than memory capacity in your computer, there are no limits of how many exposure combination you can work with. However keep in mind you can accomplish the right range of exposures in just three exposures of a scene. The trick will be to vary the range of stops between each exposure. Most if not all DSLR cameras allow you to set the bracketing steps between 1.5 and one-third stops between each exposure. There are cameras, I am sure, that allow for more ranges.

Case in point, my Nikon D90 has an automatic bracketing button used in conjunction with a command dial that allows me to customize the bracketing order and range of an image. I can then take several versions of bracketed images and then play with those in Photomatix or Photoshop later. You can cheat if you want and in RAW format only create an under and over exposed set of copies from the original image to create the same results as doing it in the camera, but once again, I’m all about doing it in the camera first.

One important thing is to set your camera to the lowest ISO possible or to use as much noise reduction as you can. Just remember, there is no one silver bullet, you will have to use a lot of trial and error. Your choice of software will vary, and every image will look best at different settings.

Summary

To start, limit yourself fewer exposures at first, and then study your final products to figure out what you need to do better. Experiment with exposure bracketing. Try different spacing, and with time you will find what works best for you in nearly any given circumstance. After all, even with HDR imaging, some people will choose to expose to fit their individual tastes. Whether it is for more shadows, or more highlights, it is all based on your personal taste of the right exposure.

To summarize, producing high quality HDR images is primarily in the range of exposures you make a scene. Whether it is three or more, expose your primary shot for the part of the scene that is most important, and bracket other exposures on either side of perfect from there. Eventually you will streamline your image capture process with custom camera functions.

There is a plethora of information both online and in print about the wide range of available software, and the process itself. Nonetheless, this is just a taste of what you can do so go ahead and use other resources, and experiment to find what works best for you! If you are a visual learner like I am, I want to direct you to a learning source I am now using to better my photography and understand my camera. Mind you I am a Nikon user and the source is geared to Nikon users. Aim your browser to; D-Town TV and be ready to take notes. I am sure that for Canon users you can find more HDR information at Digital Learning Center, Canon .

A friend of mine wrote a great tutorial on HDR and I want to direct you to his as it gets more in depth than I do, so please point your browser to,Jesse Speer's Site.