Part I of this article series showed how applying USM with a large radius can enhance small scale contrast. It is now time to determine how to choose the best Radius and Amount settings for enhancing small scale contrast.
The procedure is started by choosing the Contrast layer and zooming in to the 100% view by pressing Control+Alt+0 on a PC or Command+Option+0 on a Mac. Then, USM is launched. To make things easier to see, a fairly high Amount (for small scale contrast enhancement) will be used. An Amount of 150 will work for our purposes. It is important to understand that this Amount is being used simply to determine the best Radius setting. The Amount will be decreased before the settings are finalized. The Radius is set at its lowest setting. Finally, the Threshold is set to zero (this is the Threshold setting that is generally used for small scale contrast enhancement). The USM dialogue box looks as seen in Figure 1.
Figure 2 shows the image with the current USM settings. Since the Radius is set at the lowest value possible, not much is happening with the image. The next step is to increase the radius and watch what happens to the detail in the image. When the Radius is set to 2.0, a small amount of sharpening is noticeable (see Figure 3).
At a setting of 4.0, the sharpening increases (see Figure 4). On the other hand, there is not any noticeable increase in the small scale contrast. At a radius of 10.0, there is a small increase in the small scale contrast (see Figure 5). This is seen as an improvement in the detail in the small scale contrast areas. This is most noticeable in the delicate yellow and brown tones in middle of the large needle that runs through the center of the image. This may be a bit hard to see in these small images, but it is very noticeable on a large monitor.
At a radius of 20.0, there is a further improvement in this detail (see Figure 6). However, at a Radius of 30.0, there is actually a very small lose of the small scale contrast detail (see Figure 7).
When the Radius is increased to 40.0, there is even more lose of detail (see Figure 8). Finally, just to exaggerate the point, the Radius is increased to an extreme value of 200.0 (see Figure 9). As can be seen, the detail is further degraded.
Finding the best Amount setting for enhancing the small scale contrast is simply a matter of trying different Amount settings until a setting is found that produces the look that is desired. For this image, a Radius of 25.0, an Amount of 30%, and a Threshold of 0.0 works well. Figure 10 shows the original image with no small scale contrast enhancement. Figure 11 shows the image with the small scale contrast enhanced.
That is a nice improvement, but there is more processing that needs to be done to further enhance this image.
The large scale contrast now needs to be enhanced by adding a Curves layer (see Figure 12).
Just in case anyone has any doubts about the value of the small scale contrast enhancement for this image, Figure 15 shows the image at this point in the processing with all of the edits except the small scale contrast enhancement has been removed. Figure 16 shows the image with all of the edits including the small scale contrast enhancement.
The image with the small scale contrast enhancement is, without a doubt, superior to the image that does not have the small scale contrast enhancement. In simple terms, the image with the small scale contrast enhancement seems to pop while the other image looks rather drab in comparison.
At this point, the image is looking pretty good. One might be tempted to add a final sharpening layer and consider the image finished. However, this would be a mistake. That is because there are a couple of problems with this technique that need to be addressed. These problems, and their solutions, will be dealt with in Part III of this article series.