Handling the Details: Noise Reduction and Sharpness
One of the most useful benefits of using ACR as your HDR platform is that it has noise reduction and capture sharpening tools that exceed the capabilities offered by most Photoshop plugins. Handling noise can be a really big deal in HDR workflows.
The first thing you’ll need to do is click the Detail panel button below the Histogram (third button from the left that looks like two triangles grouped together). Next, zoom in to 100% to ensure that you’re seeing an accurate representation of how these settings affect your image. Figure 8 shows the demo image at 200%, to illustrate the noise issue that can be present, even when shots are taken from a professional DSLR at relatively low ISO settings (in this case, ISO 640).
Figure 8 When working with the sharpening and noise reduction controls, zoom to 100% or 200% to get an idea of how much luminance and color noise is present.
Because most of the details in this shot were relatively far from the camera (and it was focused to infinity), I zoomed back to 50% and then panned down to the bottom of the shot to evaluate the water details. Any changes I was going to make to the Sharpening values would be most visible in this area. Because sharpness of the water details took a back seat to the colors in this shot, I decided to make a common trade-off: relatively little sharpening for better noise reduction results.
Zooming back to 100%, I bumped the Amount value only a few points up to 40, and reduced the Radius to a slightly higher value to impact the “high frequency” nature of the details in the foreground. Finally, I needed to limit where these changes were taking place. To do this, I zoomed back out to 33% (to see more of the photo), held down the Option key on the Mac (Windows uses Alt), and dragged the Masking control to the right, until only the parts of the shot I wanted sharpened (as sharpening can make noise problems worse) showed through as white pixels in the preview (Figure 9).
Figure 9 The Masking option is a great way to avoid sharpening the more noisy regions of a photo.
For the Noise Reduction settings, I zoomed back in to 100% again, and panned to a spot where I could see noise in both the water and sky.
Next, I experimented with Luminance values between 20 and 40, and Color values between 15 and 30. Once I found the right values, I examined the details again and adjusted the Luminance Detail and Color Detail settings (which are designed to reduce the blurring associated with noise reduction), so that the highest amount of detail was maintained without re-introducing noise. Basically, the two “detail” controls create a trade-off; as they “fade” the strength of your noise reduction settings, more fine detail will remain intact, but more noise will remain intact also, potentially. The default value for these two settings is 50. You can see my results in Figure 10.
Figure 10 Take some time to experiment with different combinations of Sharpening and Noise Reduction settings when working with HDR photos.
You may think at this point the Noise Reduction workflow is done but the real test comes when you zoom back out to 33 or 50% and then turn the ACR Preview button (top-center, just to the left of the Histogram area) on and off, examining different areas of detail as you do so. What I discovered in this case was, even having applied the Noise Reduction somewhat sparingly to avoid over-softening the details, things were now too soft in the foreground. To remedy this, I reduced the Masking value slightly (thus sharpening more of the foreground details), and I increased the Luminance Details to slightly reduce the impact of the Luminance noise reduction. The final noise reduction results, zoomed out to 50%, are shown in Figure 10.
In one final tweak before working on the colors, I noticed (back in Figure 8) that the silhouetted trees had a slight purple fringe or chromatic aberration around them. To fix this, I quickly jumped to the Lens Corrections panel (fourth button from the right under the Histogram) and under the Color tab clicked Remove Chromatic Aberration, then bumped the Purple Defringe value up a point to be sure all the discolored pixels were fixed (see Figure 11).
Figure 11 The Lens Corrections panel offers the ability to remove color fringes and other chromatic aberrations within the HDR workflow.