Update: We have much more detailed HDR Education, including using HDRs for Wedding Photography, Landscapes, Buildings and more over in our School. Click here for more up-to-date HDR Education.
HDR How To
Many of you are probably familiar or have at least heard the term HDR (High Dynamic Range). However, you may not know exactly what HDR means, as well as how to shoot an HDR image. I wrote this article to provide a down to earth explanation on what HDR means, its purpose, as well as how to shoot and compose an HDR image.
First, what does the term High Dynamic Range exactly mean? Before you can learn how to execute HDR, let’s get into some definitions of HDR. Simply put, the dynamic range of an image is the range of luminosity from the darkest shadow to the brightest highlight within an image. Depending on your composition, the dynamic range can vary greatly.
For example, imagine shooting an image at your local jazz club. Most likely, the scene would be dark and moody with perhaps a few small amounts of highlights perhaps in the lighting and candles. The dynamic range in this shot would be very low since the majority of the scene is dark. On the flip side, let’s say you were shooting a very bright scene, such as just the clouds in the sky. The dynamic range of this scene would still be very low since the majority of the scene is bright.
Now let’s say you are outdoors in the mid-day sun shooting a nice landscape scene. This scene would have a high dynamic range since there would be significant amounts of bright highlights found in the sky and where the sun is directly lighting objects in the scene; and there would also have very strong shadows where shadows were being cast. This type of situation is very common and poses significant problems when the camera tries to meter the scene to the appropriate exposure.
To illustrate, while Pye was in Rancho Palos Verdes finishing up an Engagement Shoot, he stopped in a park to capture a few HDR sunset scenes for this tutorial.Â We will use these pictures throughout this article to show how scenes with a high dynamic range are difficult to expose correctly because even if you properly expose the scene based on a single exposure, you will either blow out (lose detail) the highlights and or clip (lose detail) the shadows. Thinking in terms of how film exposes, this makes sense. The highlights or bright areas of the composition are going to burn into the film much quicker than the dark shadowy areas of the image.
Using a Canon 40D, Pye took this first shot on Manual while using the Evaluative Metering mode. For illustrative purposes, the EV (exposure value) was set to what the camera was interpreting as a “proper exposure” (+0 EV). As you can see below, the dynamic range in this picture is extremely high. You have bright highlights in the sky and in particular near the sun, while you have very dark shadows in the foreground and below the horizon. In the image you see below, the sky looks okay and properly exposed, but the foreground shadows are almost completely clipped.
The question is, why did the camera interpret the picture above to be “properly exposed” when it obviously isn’t? To avoid a complex explanation, what the camera’s metering system is basically doing is averaging the light in the scene. It is programmed that on average a proper exposure should have a certain level of highlights and a certain level of shadows. If you were to average these white highlights and black shadows, the average properly exposed image would be approximately 18% gray (don’t worry if the gray thing doesn’t make sense now, it will later). So, when the camera took a reading on this scene and saw that everything above the horizon line was super bright, it adjusted the exposure so that the rest of the image would be very dark in order to “balance” out the exposure to that programmed setting. Bottom line, when shooting scenes with a high dynamic range, you need to rely more on yourself, and not on your cameras metering system.
The first thing photographers might do when they see this scene is adjust their settings to over exposure their image by a stop or so in order to bring some more detail out of the foreground. So, Pye adjusted his camera up two full stops (+2 EV) to illustrate what happens to this scene when over exposed to bring out the foreground.
In this second picture, you can see how the foreground detail was brought out. However, what happened to our highlights? Our highlights are now significantly blown out and the loss of detail in the highlights is something that cannot be repaired in post production. Now, it should be known that the nicer your camera and sensor, the better your camera will deal with high dynamic range scenes. However, the problem will always be there. So, shall we toss up our hands? Not quite yet, keep reading.
To summarize, with a single exposure, you are either going to under expose in order to recover the sky, thus clipping the shadows. Or, you will over expose and blow out the sky, while bringing out the detail in the shadows. There are three ways around this, using a gradient filter, adjusting the exposure in post production, or shooting an HDR shot.
[REWIND: Learn HDR Photography from SLR Lounge]
A gradient filter is a filter that you attach to your lens which graduates from completely transparent at the bottom, to semi-opaque at the top. You adjust the filter on your lens so that the completely transparent portion starts at the bottom of your scene. The higher up you go on the filter, the darker it gets, thus reducing the level of exposure. This exposure reduction above the horizon allows you to take a single shot and properly expose the foreground and the background at the same time.
Gradient filters are wonderful, we use them, we love them. To learn more about gradient filters and their purpose and uses, keep your eye out for an an article on them shortly. To be honest though, sometimes gradient filters just get cumbersome. Not only does a good gradient filter cost anywhere from $50-$100+, it is also another item you have to carry it around and adjust constantly with each and every scene. It can be quite a slow and cumbersome process. Now, if you only shoot landscapes then wonderful, simply screw on the filter, adjust it to your hearts content, and enjoy. However, if you like shooting landscapes, people, nature, animals, architecture, etc, then you have to be constantly removing and adding the filter to your lens. So, let’s look at another solution.
Adjusting the exposure in post production works when the image is shot RAW, is about 1-2 full stops under exposed, AND was shot at ISO 100 or less. Why? Well, you need to shoot RAW in order to retain as much image information as possible. Shooting 1-2 levels under exposed allows you to retain the highlights, without clipping the shadows too much. In addition, if you don’t shoot the image at 100 ISO or less, then as you increase the exposure in post production, you will create too much noise, thus making the picture unusable.Â Keep in mind if you clip your shadows your blow your highlights, the detail is gone and you won’t be able to bring it back in post production. While we wont go into too much detail on the nitty gritty of how to selectively raise exposure levels throughout the image in post production, we will tell you that it involves carefully selecting certain areas of the image, such as the sky or the foreground, and raising/lowering the exposure levels. In reality, what you need to know is that this process is difficult to master and extremely time consuming. So, that leaves us with option 3, shooting an HDR shot.
While we have explained what the term HDR means, we haven’t talked about how to capture and piece together an HDR image. HDR capture modes use AEB (Auto Exposure Bracketing), a feature that can be found in most nice cameras and almost all DSLRs. AEB is a feature in your camera that allows you to fire off three consecutive shots at three different exposure levels. To do so, set your cameras base exposure to “correctly” expose the scene (+0 EV) according to your camera’s evaluative metering setting. Then set your AEB to +/- 1 or 2 full stops, my preference is +/- 2 full stops.
Now, your camera will shoot one shot that will be a median exposure, followed by a shot that is under exposed by two full stops, and a third shot that is over exposed by two full stops (depending on the camera, it may not be in that exact order). The under exposed shot is going to bring out the detail in the highlights since none of the bright areas will be blown out, however it will lose all the detail in the shadows leaving them virtually black. The over exposed shot will do the opposite, completely blowing out the highlights while bringing out the detail in the shadows. The magic happens when the three shots are layered together. Once combined, you will have an HDR image that retains all of its detail in both the shadows and the highlights. As shown in the title image to this article. Read further to find out how to do this.
You can combine the three images with Photoshop layering or HDR creation software such as Photomatix. My preference is Photomatix since it gives you much more control over the HDR combination properties. Though if you don’t have or wish to buy Photomatix, we will be writing some articles in the Photoshop help section to give you a good guide to combining the HDR image via Photoshop.
To create the image, simply shoot your scene using your cameras HDR mode. If you don’t have an HDR mode, keep in mind that you can adjust the exposure manually in between shots. If your camera has a very fast shutter speed (7+ FPS) you may be able to get away with simply holding your camera extremely steady as you fire the three HDR shots. However, we always recommend you use a tripod (such as SLIK 615-315 Professional Photo/video Tripod) when shooting HDR shots since even a slight amount of hand shake will create less-than-tack-sharp results when you layer the images. Furthermore, for those of you whose cameras don’t have a fast shutter speed, and/or the HDR mode, you must use a tri-pod so that you can adjust your settings and fire off the exact same shot at a different exposure level.
Once you are happy with your three AEB images, upload them to your computer and load up Photomatix. Once in Photomatix, generate a new HDR image from the HDR Menu and select the three images that you uploaded. If it cannot detect it automatically, it will ask you to define what the AEB settings were, i.e. +1 / -1 full stops or +2 / -2 full stops. The images will load and be combined into one single image in Photomatix. At this point, you will know if you had too much hand shake, because despite Photomatix‘s best attempt to align the image, the image may appear blurry or less-than-tack-sharp. If this is the case, then go back and reshoot the scene, this time with a tri-pod.
If the image meets your desired sharpness, then from the same menu, apply your desired Tone Mapping settings in order to recover the highlights while bringing out the detail in the shadows. While you are in the Tone Mapping panel, you can also adjust the strength, saturation and other options in order to get the image to your tastes. You will need to play with the different tone mapping settings in order to get a feel for what each does. The title image in this article is fairly “candied” as we would say. This was done to really show off all of the unique colors that were in the scene. However, we typically prefer a “less-is-more” style. And keep in mind that you can make the image as candied or as subtle as you like, though you may not want to make the image scream “HDR” as any professional photographer and a lot of informed consumers will be onto it right from the start.
Once completed, you can export/save your file and viola! You now have created your first full HDR image.
While this guide will give you a nice high level overview of HDR photography, you can get an incredibly detailed look into HDR photography here at NatureScapes.net.
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