The Problem in Standard Photography
On every single-exposure photo a photographer will always have to balance highlight areas and shadows. For most regular photos, a decision has to be made on whether detail should be seen in the dark areas or in the bright areas. If the dark areas should be correctly exposed in order to show detail in these regions, it is likely that the longer exposure will overexpose the bright areas of the scene (blown highlights). However, if detail is required in the highlight areas, the shorter exposure that is therefore necessary will most likely render shadows too dark, hiding detail of these regions. The photos below have been kindly provided by professional photographer James Murray (www.thinkjamesphoto.com) and show this effect of both over- and underexposure. You will notice how the overexposed picture provides a very good level of detail of the darker structures. The underexposed version of the same scene provides better detail of the bright areas (glass surface and sky).
The reason of this conflict is the limited dynamic range that camera sensors usually have (contrast ratio of around 4.000:1 for a 12-bit camera sensor). Real scenes usually present a dynamic range that is much larger than the capacity of the camera sensor (contrasts up to 60.000:1). In most cases this is no problem, because just a little percentage of the picture will lose detail, however there are fields of application, where a consistently high level of detail is required throughout the photos.
How High Dynamic Range Photography helps
With the problem of standard photography mentioned, there is still a way to get detail of bright and dark areas in one single picture. It is therefore neccessary to capture more than one picture of the same scene, but with different preferences. Each picture should be differently exposed, so that one picture shows detail in dark areas, another picture in midtone areas and another picture in bright areas. The post-processing of these (typically three) pictures can blend these multiple exposures of the same scene to one single image that more closely reproduces the dynamic range that was available in the original scene. The image below demonstrates the increased level of detail in a High Dynamic Range Image.
Fields of application
The important question is when to use High Dynamic Range Photography. Not every scene is suitable for this technique, and many scenes even do not require HDR Photography.
Suitability: The HDR camera setup requires to take several pictures of the same scene. To be able to merge these multi-exposure pictures into an HDR file, it is required to have both the camera and the scene not to move. While the camera movement can be controlled by using a tripod, the scene movement sometimes cannot be prevented. While minor movements of little objects can be retouched in the HDR software, major object shifts will make the single exposures unable to match each other. For this reason, mainly unmoved scenes are suitable for capturing with HDR Photography.
Necessity: While an increasing number of today’s photos is taken with HDR techniques, not all scenes actually provide an extremely high dynamic range. Imagine a foggy scene where no direct sunlight and no bright reflections can be seen. The dynamic range of the camera sensor will most likely be sufficient to capture the atmosphere without losing detail. Also, even with brighter areas available, many photographers prefer to have dark areas to cause strong contrast in the pictures. Shadows and highlights can be a very useful stylistic device to direct the viewer’s eye into the most important area of the picture. It should be a careful decision whether to create an HDR Photo of a scene or not. For some applications however, it is desired to show as many detail as possible.
Here is a list of very good instances that can benefit from the extra spectrum of light:
- Architecture Photography
- Interior Design
Requirements to shoot HDR Photos
- Camera with automatic exposure bracketing (also possible without, but highly recommended)
- Tripod (also possible without, but highly recommended)
- Remote Shutter Release (also possible without, but recommended)
- Software (required)
1. Choose the right scene
As mentioned before, the effect of High Dynamic Range Photography will become most obvious with scenes that have both extremely bright and extremely dark areas of interesting detail to bring out. So choosing the right scene is an important first step. Regardless of the brightness levels, quickly moving scenes are not recommended, but slow movements can be reduced later.
2. Camera stabilization
In order to create several images that can be merged later, it is quintessential that both the scene and the camera do not move. The camera should be stabilized by lying it down on a solid surface, however it is recommended to use a camera tripod. A tripod prevents the camera from falling off improvised camera stands and allows precise angle adjustments including leveling and tilting.
Another very important step to improve HDR photos is to switch off the image stabilizer of the camera lens, if available. It may sound counterproductive to switch off a device that is meant for stabilizing the picture, however image stabilizers are constantly trying to sense vibrations to compensate by the stabilizing lens unit. If the camera rests on a tripod, no environmental vibrations can be felt by the image stabilizer, making it vulnerable to overreact to self-induced vibrations such as those caused by the camera’s flipping mirror. This is the reason why the image stabilizer should be turned off while taking High Dynamic Range Photos.
Reduce vibrations: Live View Mirror Lock Up
3. Exposure settings
Depending on the dynamic range within the scene, different exposure brackets may be required. If just a little more detail is desired in bright and dark areas, it can be sufficient to over- and underexpose for one exposure value. Combined with a default exposure (0 EV) there will be three resulting exposures (-1 EV / 0 EV / +1 EV). To capture the largest dynamic range, it is usually recommended to use a -2 EV / 0 EV / +2 EV exposure bracket series. There are two ways to control the exposures.
- automatic exposure bracketing If your camera features automatic exposure bracketing (called AEB on Canon cameras), it is recommended to use it. The automatic exposure bracketing menu usually allows to choose the additional exposure stops. Some camera models even provide exposure brackets of more than three exposure stops, expanding the dynamic range even more. The automatic exposure bracketing will shoot the photos in a quick sequence by just pressing the trigger once. (note: some Canon cameras will not shoot a sequence unless a self-timer is used!).
- manual exposure bracketing
–ZZ–ZZ–ZZ–ZZ–If you don’t have AEB, then take a photo, adjust the shutter speed one or two stops faster (i.e. if you’re at 1/250 sec, go to 1/500 or 1/1000 sec), take a photo, then adjust it one or two stops slower than your original shutter speed (i.e. if you were at 1/250 sec, then set it to 1/125 or 1/60 sec), and take another photo. You will now have three photographs: one overexposed, one underexposed, and one normal. Manual exposure bracketing can be more time-consuming and require the scenes to be extremely static, however it allows more exposures than automatic exposure bracketing as many cameras simply allow three brackets. Also, manual exposure allows some more experiments with the scenes, such as adding light to one image and leaving light on another, merging all parts in post-processing software later. The more source images you have the better.
Important: Autofocus off. The focus may not change between the images!
It is recommended to shoot in RAW format. Most post-processing software can handle RAW files, and the extra bit rate can pay off in some scenes.
5. Shutter release
Releasing the shutter by simply pressing it on the camera can cause the tripod to vibrate. This can result in the exposure bracket series to be slightly unaligned. For this reason it is recommended to use the self-timer function of the camera, giving the tripod enough time to decay the vibrations until the exposure bracket series begins. An alternative to the self-timer is a wireless remote shutter release that can trigger the camera without touching it. There is also various software available for Smartphones that can be connected with Cameras via USB cable or wireless channel, if available on the camera. It can be of some advantage to control all camera settings via Smartphone – especially when manual exposure bracketing is the method of choice – to avoid the tripod to move when changing the settings.
6. Software Post-Processing
The last and most creative step is to create and tone-map the actual HDR Photo.
- Manual Post-Processing
- Automatic Post-Processing: Photomatix Pro
Having compared many post-processing programs in the past, I can highly recommend Photomatix Pro (www.hdrsoft.com) as a professional tool to create stunning HDR pictures.
Here is some basic information on Photomatix Pro:
- available for Windows and Mac
- older versions can be downloaded for compatibility reasons
- example images can be downloaded for tone-mapping attempts
- the website features an informative resource area with a collection of online articles and professional tutorials on HDR photography.
- excellent program documentation including a changelog, user manual with step by step explanations, in-application explanations of features etc.
- also comes in a light version (Photomatix Essentials) for a reduced price.
- easy to use
- allows batch-processing
- plugins for Photoshop and Lightroom available
- many pre-installed templates
- allows to save own templates
- allows to select the number of CPU cores used.
What it can do:
- creates HDR images
- tone mapping and fusion
- automatic alignment of handheld images
- automatic and manual de-ghosting
- reduction of noise and chromatic aberrations
Here is a short tutorial on how to create an HDR image using Photomatix Pro: