Local Contrast Enhancement
Submitted by mitch on Fri, 11/14/2008 - 21:47.
The source for this tip is a recent thread on Phil Askey's site, Digital Photography Review. Someone asked about using sharpening to enhance image contrast.
(If you have not visited "DPR," I encourage you to stop by. Phil offers very thorough reviews of new digital cameras. His forums are definitely among my personal favorites, too.)
You can indeed apply sharpening in a way that adds to the perceived contrast in an image. I don't take credit for the technique. I learned about it from Michael Reichmann on his site, The Luminous Landscape. Michael credits Thomas Knoll, the father of Photoshop, with the technique.
The technique is simple. Best of all, the technique works!
You use the Photoshop Unsharp Mask (USM) filter with a low setting for Amount and a high setting for Radius. Good starting points are Amount = 10 or 20 and Radius = 30 to 60.
Why low Amount and high Radius? Those settings increase contrast along the edges of small details. As Michael Reichmann notes, when you increase contrast along small adjacent areas, the shadows and highlights appear broader to our eyes.
Still dubious? Here is an image after basic adjustments. I use a two-stage or three-stage sharpening workflow, which you can read about in my sharpening tutorial, "Put a Fine Edge on Your Sharpening Skills." The image already has received a round of capture sharpening.
The image is reasonably sharp. Capture sharpening is light sharpening. Just enough to restore sharpness lost during digital capture.
The next image shows the result of USM settings Amount = 10 and Radius = 20.
The image is visibly sharper. This is most evident in the texture of the log. Contrast also shows a slight improvement. Don't expect the increase in perceived contrast to be readily apparent. The improvement is subtle, but perceptible.
Let's see what happens when USM settings are Amount = 20 and Radius = 50.
There's even more contrast in the fine details. Especially in the lighter striations along the log.
I often apply a round of Local Contrast Enhancement just before I apply output sharpening. When I sharpen for the Web, I can often get by without a final output sharpening layer. Local Contrast Enhancement suffices. Output sharpening needs to be specific for the output device, however, so expect to apply a light round of output sharpening before sending your image to a printer or film recorder.
Please, go take a look at Michael Reichmann's article, "Local Contrast Enhancement." Thanks to Michael and to Thomas Knoll for a technique that's easy to apply to improve our images!
Cheers!
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Hi Mitch,This is one of my most used actions or scrips
Hi Mitch, This is one of my most used actions or scrips as I use it as part of your Sharpening Scrips. Really makes the images pop and I find it just adds that final touch. Good action all round. Cheers Jess.
Re. Hi Mitch,This is one of my most used actions or scrips
That's good to hear. It is an effect that I like a lot. I use it on most of my photos. It sounds like a screwy idea at first, but it really does work. It's one of the best tips I ever read. Here's the link to Michael Reichmnn's essay:
http://www.luminous-landscape.com/tutorials/contrast-enhancement.shtml
Local contrast and clarity
Mitch,
After reading your article on local contrast I started playing around with it on some of my pics. I'm really impressed with the difference it makes. Then I played a little with your clarity script, and it seems to me to have a slightly stronger effect, at least on the images I tried. So I have some questions.
1. Are there any downsides to these techniques? They seem almost too good to be true.
2. Are there guidelines as to where you might use local contrast vs. clarity?
Anyway thank you for publicizing these techniques and providing tools for them.
Bob Roby
Re, Local contrast and clarity
I learned the Local Contrast Enhancement technique from Michael Reichmann. He attributed it to Thomas Knoll. He used USM with a low Amount and a wide Radius setting. I learned about the internals of the Clarity slider from a forum posting somewhere by Jeff Schewe. He attributed it to Mac Holburn at Nash Editions. It uses High Pass with a wide Radius and then midtone roll-off through Belnd If settings. They both do the same thing. The effect is stronger with the settings I used with TLR Clarity. But it is also more easily modified. You can change the layer blend, the layer opacity, or the Blend If settings. I use them as creative sharpening effects. So I apply them after adjusting color and tone. They are the last thing I add to my master photo. I save that as a .PSD file. I then work on a flattened version after that for output. Cheers, Mitch
Thanks Mitch..
The clarity script is really slick.