Most photographers are familiar with the limitations of modern cameras. Often we encounter scenes with a high dynamic range that forces us to expose for the highlights (or shadows) and work on a fix in post-production. Important details are lost when we do this. The High Dynamic Range (HDR) process attempts to solve this problem by combining a series of raw exposures to create a single image that displays a scene similar to how our eyes would perceive it. This article assumes basic knowledge of creating bracketed exposures (either manually or automatically) with your DSLR, as well as basic knowledge of RAW processing with tools like ACR or Lightroom, and editing with curves adjustments.
Here are a few of the things you need to keep in mind when working with multiple exposures for HDR:
• Do not change the focal length, focus point or aperture when creating a series of bracketed exposures.
• If your DSLR supports it, use the full frame or “matrix” metering mode.
• Use a tripod or Vibration Reduction (VR) lens if you can. Camera shake can cause problems in HDR.
• It’s OK to make a few RAW edits before merging to HDR; just be sure to synchronize the edits, and stick to settings that do not affect contrast or color (I usually apply a crop and noise reduction.)
Photoshop offered basic HDR tools in the past, but it was not until Photoshop CS5 that we were given a complete set of tools for making HDR images. To start, choose File > Automate > Merge to HDR Pro. From the dialog that appears, choose a series of bracketed exposures from your hard drive and make sure to select “Attempt to Automatically Align Source Images” before beginning. Note: the process of merging your documents may take a minute or two, depending on your system hardware.
The controls for Merge to HDR Pro (Figure 1) are broken into three areas: a large preview, tone-mapping and color controls, and a series of thumbnails representing the shots that are being merged together.
A. Remove Ghosts—“Ghosts” refer to a faint blurring effect that can occur when Photoshop tries to reconcile areas of the frame that contain subject matter which changed position from one shot to the next. Examples of ghosts can include things like moving clouds or even an object that passed by your lens. Most of the time it makes sense to select this option. Choose which image will serve as the “still” for your HDR exposure by clicking one of the thumbnails (see item F).
B. “Mode” Menus—Photoshop CS5 can create 8, 16 or 32-bit HDR files. Depending on which bit- depth you choose, different tone-mapping modes are available. By default, Merge to HDR Pro displays controls for a 16-bit, Local Adaptation workflow. Since this combination offers the most powerful features for defining an HDR image and provides an easy transition to a 16-bit workflow, this is the mode I typically recommend.
There are three additional conversion options for 8 and 16-bit modes: Equalize Histogram (an “averaging” of the data), Exposure & Gamma (uses a Gamma slider to set the white point, and an Exposure slider to handle overall brightness), and Highlight Compression (“averaging” that attempts to avoid clipped highlights, usually resulting in relatively flat contrast).
C. Edge Glow Controls—These sliders control the edge contrast and glow effect in the scene. The Radius defines how far from the contrast edge the effect will be shown, and the Strength defines the amount of glow. My preference is to avoid the type of HDR images where the glow is so pronounced that it changes the photo from real to surreal. Experiment with these sliders to suit your tastes.
D. Tone & Detail Controls Gamma helps establish the overall tonal balance of the scene and can help to avoid blown highlights when working with the other sliders.
Exposure works much like the Exposure slider in the Basic panel of Lightroom and ACR, except that it has a greater effect (relatively speaking) on Highlights than on Shadow details.
Detail provides roughly the same functionality as the Clarity slider in the Basic panel of Lightroom and ACR, enhancing mid-tone contrast edges. However, Detail can have a much more pronounced effect.
Shadow will brighten or restore detail to the darkest areas of the image (drag to the right) without flattening the overall contrast.
Highlight allows details in very bright areas to be recovered without flattening contrast. It works like the Recovery slider in Lightroom and ACR.
E. Color & Curves panels—We also have controls for enhancing color intensity in the image (Vibrance and Saturation—just as in ACR or Lightroom), as well as making precise corrections to the tonal range with Curves and Corner points. These will be discussed shortly.
F. Exposure Thumbnails—Used to include or exclude specific shots in a bracketed series and to select the “base image” when removing ghosts.
Once you’ve merged your exposures and removed any Ghost artifacts, you can begin the HDR edits. I find that it’s helpful to first set the global contrast and overall clarity or detail (Tone & Detail controls) before I begin experimenting with the Edge Glow effects, because those usually have an impact on maintaining the brightest highlight details.
To set the white point and define brightest details in the scene, drag the Gamma slider down to about .7 and then slowly work the slider back to the left until the brightest details are intact but slightly underexposed. The idea is to leave a little “head room” so that if you need to boost the Exposure value to brighten the middle tones in the scene, you can do that and then use the Highlights slider to recover any blown highlights (Figure 2).
Next, examine the shadow areas of the image and determine if they need to be brightened using the Shadow slider. Typically you need to set the value fairly high to reintroduce details that have been “lost in the shadows”. Zoom in if needed to make sure a smooth transition between light and dark detail is maintained, then zoom back out to look at the shot with normal magnification before moving to the Detail control.
The Detail slider will enhance the apparent sharpness of image details by increasing the contrast edges in the midtone areas. It can also be used to smooth out details (for portraits and other situations where a high degree of textural detail may not be desirable). It works on the same principle as the Clarity slider in Lightroom or ACR, but has a more pronounced effect at higher settings. For landscapes and architectural subjects, a modest increase in Detail will often give the composition added dimenson. The default Detail setting is 30%.
The Vibrance and Saturation sliders serve the same purpose as their namesakes in Lightroom and ACR—modifying the color intensity in your image. Vibrance does a better job of increasing or decreasing the intensity of skin tones and earth tones without creating unwanted color shifts or artifacts. Typically I make smaller adjustments to the Saturation slider and make the more pronounced changes with Vibrance (Figure 4). The default setting for Saturation is 20%.
Curves & Corner Points
Once you’ve handled all the other settings, use the Curve panel to make adjustments to specific tonal regions in the image. The curves UI in Merge to HDR Pro may look a little rudimentary, but it is very powerful. As you place points on the Curve, click the Corner option. This will allow you to place additional points on either side of the Corner point and make changes, without affecting the opposite side (as it would with a normal curves controller). Figure 6 shows a series of regular points and corner points, making it easier to create pinpoint tonal edits with the Curves panel. Figure 7 shows the final HDR image after being processed in Merge to HDR Pro.
Adding Edge Glow
Once you’ve created the global contrast and color for your scene, start experimenting with the Radius and Strength settings to create any subtle “glow” that you wish to create. Often I make additional, minor adjustments to the Gamma and Highlight settings, as well as Detail, to prevent the glow effect from blowing out highlights or taking on an unrealistic appearance. In my experience, I’ve found that Radius values between 50 and 150 produce pleasing results for landscapes and architectural subject matter, with Strength values between .40 and 1.5, but it’s definitely more an art than a science. Figure 5 shows the Edge Glow settings (and final Tone & Detail settings). Notice how the clouds and lighthouse now have a more dramatic contrast.