HDR software is most typically used to render shadow and highlight detail, but it can also be used to enhance tonal separation and detail in any range of tones, even in images with extremely low contrast. The very same tools that are used to compensate for HDR side effects can be used to sharpen any image.
When multiple bracketed exposures are merged into a single processed file, shadows and highlights that exceed the dynamic range of a camera’s sensor are compressed into the dynamic range of a digital file, taking the midtones with them. Depending on the HDR software used, a variety of tools are available to restore contrast and separation in midtones. If used aggressively, these tools produce the tell tale signs of contemporary or grunge HDR artifacts – halos and texture accentuation. These are the very same artifacts that digital sharpening routines use more conservatively to make images appear sharper – only they look different.
Unlike the hard halo and line produced by the filter Unsharp Mask and more like the soft line produce by the filter High Pass, HDR sliders can give you still more points of control over line and texture, each with a slightly different flavor.
For creative sharpening, compare two HDR software packages; Adobe Photoshop and NIK’s HDR Efex Pro.
Adobe’s Photoshop’s HDR solution offers three points of control relevant for sharpening. One, Radius controls the thickness of the halo / line. Two, Strength controls the contrast of the effect. These two sliders are similar to the filter Unsharp Mask but the effect is much closer to the filter High Pass. Three, Detail accentuates texture, with minimal affects on contours. Unlike the filter Unsharp Mask’s Threshold slider, instead of suppressing the side effect of texture accentuation, this slider gives you the ability to control it independently of contour accentuation. (Settings lower than 100% blur the image but not its contours.) Photoshop typically offers the smoothest continous tone effects.
While NIK’s HDR Efex Pro presets are rich and wonderful for visually exploring tone mapping variations, for detail enhancement you really only need to focus on two features. First, the Method, which set the base effect; Natural, Clean, Crisp, Halo Reduction, Subtle, Sharp, etc. Second, the Structure slider, which functions very similarly to Viveza’s Structure. Structure accentuates texture somewhat, which can enhance noise as well as detail, but not as much as Unsharp Mask. When Structure is applied, luminosity contrast increases, more so in shadows than in highlights where very high values stop just short of compromising shadow detail. Unlike, Viveza’s Structure, the effects on shadows and highlights can be modified with HDR Efex Pro’s Blacks and Whites sliders. Think of Structure as occupying the visual territory that lies between Unsharp Mask and High Pass. HDR Efex Pro’s interface is simple yet more versatile, which means you’ll spend a little more time exploring the many options it offers.
(HDRsoft’s Photomatix is an excellent for tone mapping but it is difficult to separate contour and texture from tonal enhancement, making it an overly challenging addition to sharpening solutions.)
If sharpening is your goal, resist the temptation to use the other sliders in each interface; they won’t enhance detail only contrast. That said, much like Photoshop’s simpler TMO Shadows/Highlights they can be used to render shadow and highlight detail more clearly.
Once images are sharpened with HDR software, the rendered effect can be layered with an unsharpened version of an image, providing more control. Use the blend mode Luminosity to affect only the light and dark values. Use the Opacity slider to reduce the effect. (Knowing you can only reduce the effect, you’ll favor applying the HDR software a little aggressively.) Use the Blend If sliders to remove the effect from either highlights (halos) or shadows (lines) or both. Mask the layer to apply the effect to selected regions. You may even decide to use two (or more) different layers with different HDR treatments to customize effects for specific image regions.
And, of course, sharpening with HDR software can be used in combination with any other sharpening technique, like Unsharp Mask or High Pass filtration.
The options you have for controlling the look and feel of detail in your images are simply unprecedented in the history of the medium. Every digital artist will benefit from exploring these options.
1 Unsharpened image.
2 Photoshop’s HDR dialog box.
3 Sharpening with Photoshop’s HDR.
4 NIK’s HDR Efex Pro Method choices.
5 NIK’s HDR Efex Pro Structure slider.
6 Sharpening with NIK’s HDR Efex Pro.
7 Image sharpened with multiple HDR applications.