HDR Tutorial Part 1: Introduction

HDR or High Dynamic Range, is probably one of the most hyped aspect of digital photography at present. It is also one of the most abused technique. If you are reading this then you probably already know something about HDR. This tutorial will be broken down into several parts and will attempt to provide techniques of proper HDR photography. If you expect wacky, cartoonish photos in this tutorial then sorry to disappoint you but you will have to look elsewhere. Please visit my Flickr HDR gallery for examples of my work. Some of them are my early HDR attempts so you will find wacky photos in there as well.

Why HDR? There are countless “reasons” as to why someone would want to use this technique. Here’s some of mine:

  1. No camera is good enough to record what our eyes can see. Our eyes are way better than any camera sensor in terms of capturing levels of light intensity. It can record about 40 stops while the best cameras can only do about 11 to 12 stops. So really, to capture a high contrast scene you would need at least 5 shots of different exposures with a bit of overlap.
  2. There are ways to overcome the limitations of #1 and that’s with the help of filters. A GND filter for example will allow you to properly expose the foreground and sky. GND filters though are good only if you have an unobstructed horizon. To be honest, I don’t use any filters except for the standard UV filter that I use to “protect” my cheap lens.
  3. I want to add some “punch” to my photos if the lighting condition is a bit flat.

When should you NOT use HDR? I always consider the following:

  1. If I can capture the entire dynamic range of a scene with a single shot then I won’t even bother with HDR, granting that my main subject is properly exposed. Beaches are easy subjects because the reflectance of sand is almost equal that of the bright sky. As long as the main subject isn’t under a shade then a single exposure might do the trick. I find single exposure shots so much cleaner than those made with HDR. I’m sure others would argue about this.
  2. Portrait shots. If the subject isn’t properly exposed then you have bigger problems. Learn to use flash or reflectors. This is the best site to read about proper lighting techniques: http://www.strobist.blogspot.com/.

So the basic goal of HDR is proper exposure of your subject. The goal may also extend to the proper exposure of the entire scene. The latter is usually what most people aim for. So we define what it means by correct exposure. In simple terms:

  1. The main subject has the correct color rendition. If it is white then it should appear white, if it is dark then it should appear dark. Simple as it seems, this is one of the most overlooked aspect of photography. White clouds or snow that look gray, a red flower that appears washed out and so on. Even with advanced matrix metering systems, correct exposure compensation is essential.
  2. There are no deep shadows or blown up highlights. This is very difficult to achieve in high contrast scenes and this problem will be our main focus in this tutorial.

Let’s talk about tools.

A good tripod is essential especially for landscape shots. Use the camera’s timer or cable to trigger the shutter release to minimze shake. If a tripod is not available make sure that your shutter speed is fast enough. Rule of thumb is 1/f, where f is the focal length. For example, if you are shooting wide at 28mm then shutter speed should be 1/30s or faster. For me, this shutter speed is still tricky for handheld shots even with image stabilized lenses.

A camera with auto exposure bracketing (AEB) would be very nice although not necessary. AEB will automatically take 3 or more shots with variable shutter speeds in succession in a single press of the shutter. I like how my Canon 40D allows me to couple AEB with the timer.

HDR software. My tool of choice is Photomatix. Another excellent tool is EasyHDR. There are others that you can download for free. I will list some of the tools at the end of this tutorial.

Photo editing software. Nothing beats Photoshop but it’s not the only tool. Paintshop Pro is very good. The free open source tool called GIMP is also very capable although it’s still limited to 8-bit colors.

Now we discuss the real stuff, HDR photography.

Just to illustrate how limited the dynamic range of a camera sensor is, go inside a house and take random shots but make sure that the entire frame includes an open window or door. Preview your shot in your camera’s LCD and you will probably notice that most of whatever is outside that window is just pure white (photo #1). If the image does show what’s outside the window, almost anything inside the house will probably be hidden in deep shadows (photo #2).  The issue is that the scene has high contrast. Outside the house is very bright compared to what’s inside. No known camera sensor could handle this at all. Normally, we would be throwing away both shots. This is the problem that HDR attempts to address.

With HDR, we could still salvage that scene by using both the same “useless” shots shown above. In HDR photography, multiple shots of different exposures are merged into one.

I would like to discuss this tutorial as scientifically as possible which means we need to understand how to read the histogram of our shots. A histogram is a graph of (light) intensity distribution as recorded in the image. Allow me to explain: the histogram has left and right borders. To the extreme left is pure black or dark or deep shadows. To the extreme right is pure white or blown up highlights. You guessed it, the middle is grey. This means a properly exposed shot of a white sheet of paper would show points to the extreme right of the graph and nothing on the left. A properly exposed shot of a black cloth would be the opposite. Photo #1, above, would therefore have a histogram that is biased to the right while photo #2 will have lots of points to the extreme left. Our goal is to make sure that NONE of the image “points” or pixels lie in either extreme left or right. Everything has to be within the middle of our graph. A scene that has good exposure would be represented by a histogram that approximates a bell-like curve. Therefore, we need to always check our histogram. Make sure that you understand this part as it is very crucial to proper HDR technique.

Now let’s concentrate on how to take the shots that we need for HDR. Set your camera to aperture priority mode or full manual mode. Select your desired aperture value. For landscape shots, this is usually set to f8, f11, or f16. Then, take multiple shots of different exposures by varying the shutter speed. The first shot is what we call our EV0. This is the normal shot that the camera meter sets the shutter speed into if you are in aperture priority mode. In manual mode, this is the shutter speed that best exposes the scene. Let’s say our EV0 is f11 at 1/125. Look at the histogram display of this image in your camera. The graph will probably have lots of points to the extreme right and/or extreme left. If it doesn’t, then you are lucky because life would be so much easier. For those unlucky souls, we would need to expose for the shadows and highlights. In aperture priority mode use exposure compensation to adjust the shutter speed. Depending on the scene, you would normally compensate at -1 and +1 or -2 and +2. The compensated shots are your EV-1, EV+1, or EV-2, EV+2, respectively. In full manual mode, you will have to set the shutter speed by halving or doubling the values. So we have, EV0 at 1/125, EV-1 at 1/250, EV-2 at 1/500, EV+1 at 1/60 and EV+2 at 1/30. By the way, always shoot with RAW image quality otherwise you will also have to manually set your white balance. RAW allows you to change the white balance later which you can not do easily with JPEG shots.

What we have done basically was to make sure that any deep shadows in EV0 are correctly exposed by the EV+ shots and any blown up highlights are correctly exposed by the EV- shots. In the photos shown above, photo #1 is EV+ and photo #2 is EV-.

The procedure above sounds complicated to some people. That is why if you are serious about HDR photography, you will need to invest in a camera that does AEB. With AEB you just set your aperture then click and hold your shutter once and the camera automatically captures EV0, EV- and EV+ for you. Easy.

Now imagine if we can choose specific parts of the EV- and EV+ shots so that we don’t have deep shadows and no blown up highlights in our final image. This process is called tone mapping. You can actually do this manually using layering techniques in Photoshop but it is very tedious. A better way is to use an HDR software which will automatically merge all shots and perform advanced tone mapping for us. This is what I will cover in part 2 of this tutorial. We will look into merging our photos using Photomatix. Stay tuned and happy shooting!

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