The modern digital camera is an excellent example of imaging technology, but the human eye can still do better. Take dynamic range, which is the difference between the brightest and the dimmest object that can be perceived in a scene. A point-and-shoot camera might achieve 256:1; a top-end digital SLR, 2,000:1; and the human eye, 10,000:1.
This 10,000:1 contrast ratio matches the dynamic range of a high-contrast daylight scene. This means there are still some scenes that we can see perfectly yet, when photographed, display black shadow areas devoid of detail and/or bright white areas.
High-dynamic-range (HDR) photography is a technique designed to overcome this limitation. It permits a scene to be reproduced as it appears to the human eye, but it can also go beyond this to produce some truly dramatic results.
You can create HDR effects with even a fairly ordinary digital camera. The secret is to take several photographs of the same scene at different exposures, typically -2EV (two stops underexposed), 0EV (exposed normally) and +2EV (two stops overexposed). The 0EV shot will show most of the scene correctly, the -2EV image will reveal detail in the highlights, and the +2EV one will record detail in the dark areas. Between them, these photographs contain all the information necessary to produce an HDR image.
The creation of that image is carried out using dedicated HDR software, which combines the images so that the best parts of each are incorporated.
Having created an HDR photograph, we’re faced with the unfortunate fact that neither an LCD monitor nor a print has sufficient dynamic range to reproduce it correctly. The final step, therefore, which uses the technique of exposure fusion, tone compression or detail enhancing (often referred to as tone mapping), processes the image in such a way that it can be viewed on an ordinary monitor or as a print.
Create images with HDR
Step 1. The HDR software we’re using can correct any alignment errors between our three photos, but better results are achieved by eliminating these problems at the outset. Mount your camera on a tripod and stand it on a firm, level surface to prevent it moving while you compose and capture photographs.
Step 2. If there’s enough light, select a low ISO value such as 100. The lower the ISO, the less image noise will result. This is particularly important in HDR photography, since the tone-mapping process has the effect of adding noise. Turn off the flash to prevent your camera compensating for underexposure.
Step 3. Set up your camera to operate in aperture priority mode. This way, when you alter the exposure compensation the aperture will stay the same and the depth of field will remain constant. This is important, since differing depths of field will prevent the photos from exactly matching each other.
Step 4. If available, use your camera’s automatic exposure-bracketing mode to shoot at -2EV, 0EV and +2EV simultaneously. You need only take one shot, but the camera will capture three versions of the scene. This method allows you to use a remote control to further reduce the likelihood of movement between exposures.
Step 5. If your camera doesn’t have such a mode, or its bracketing settings don’t go as far as -2EV and +2EV, you’ll need to take three separate photographs. Set the camera’s exposure compensation to -2EV and take your first shot. Set it to 0EV and shoot again. Finally, select +2EV and take your third shot.
Step 6. Transfer your photos to a PC, then view them in full-screen mode before performing any edits. This will help you get a better understanding of HDR. In the +2EV photo, note the detail in the shadows and the burned-out highlights. In the -2EV image, you’ll see detail in the bright areas, but almost black shadows.
Step 7. Launch Photomatix Light. Click Browse, hold down Ctrl to select all three photos, then click Open. Thumbnails of your images will now display onscreen. If you’ve added more than three images, use the preview to see what they look like when combined; the tick boxes let you exclude any shots you don’t want to use.
Step 8. Rather than navigating to the images on your hard drive and clicking Open, as described in Step 7, you can quickly upload images simply by dragging-and-dropping them into the grey area of the window. If you use a photo manager such as Exif Pro to view, manage and select your photos, this method may be preferable.
Step 9. Click Next. In the following screen, ensure ‘Exposure Fusion’ is selected at the top left. This method produces the most realistic-looking results; to create the classic HDR effect using the ‘Details Enhancer’, see Step 11. Fine-tune your image using the sliders provided on the left until you’re happy with the preview.
Step 10. Click ‘Process and Save’. Photomatix offers a choice of export file formats, including Jpeg and 8- or 16bit Tiff. Note that although 16bit Tiff is sometimes considered a native HDR format, you won’t gain anything from using this since the effect has been processed to be viewable on a normal monitor or in print.
Step 11. It’s also possible to create an HDR image using Photomatix’s ‘Details Enhancer’ mode, which uses the classic tone-mapping technique. Having already imported your images, select ‘Details Enhancer’ from the top left of the second screen. Your image will immediately look more dramatic in the preview window.
Step 12. Photomatix uses default settings to produce the least bizarre result, but you may like to experiment with the program’s ‘Painterly’ and ‘Grunge’ settings. The sliders provided on the left vary slightly in each mode, and the image shown in the preview mode will show an increasingly dramatic effect.
Step 13. You can create a custom tone-mapping effect with various combinations of settings using the sliders provided on the left. To start, this will largely be a matter of trial and error, but note that helpful descriptions of what each setting does are provided at the bottom left of the window as you hold the cursor over them.
Step 14. If you want to give the HDR treatment to a photo which you hadn’t had the foresight to bracket, all isn’t lost. Although the result won’t be as good as with an exposure-bracketed set of three photos, you can get impressive results using a single shot. Select a single photo in step 7, then follow steps 11, 12 or 13, then 10.