Smarter Sharpening: Sharpening For the Image at Hand - Part I
I do not believe in the use of a single tool for every job. I would love to use a hammer all day long at the office... believe me... but I doubt that it would help me to solve more than one or two "problems" each day. Sharpening of digital images is a problem that strengthens my belief of wielding many tools.
Not many of my images are identical, so it stands to reason that not all of their sharpening requirements will be identical. I will write several articles, like this one, detailing the tools and methods I apply to sharpening various images from my collection. For each article, I will select an image that requires special attenion in some way that calls for "smarter" sharpening methodology. My hope is that these articles will sway you from employing single sharpening solutions. Unsharpen Mask, 200% at .5 pixels. Sound familiar? I bet it does!
So, I knew immediately that the image below was a keeper. However, detailed fur against a smooth background would present some problems when sharpening the image. While I wanted to sharpen high contrast edges throughout the marmot's coat, i did not want to add any noise or sharpening artifacts to the rest of the image, especially within the background. Applying sharpening globally would do just that. How would I avoid this?
Some time ago, I learned of a two-pass Photoshop sharpening method developed by Bruce Fraser. It involves using Photoshop's "Find Edges" filter and would allow me to avoid sharpening areas of my image without discreet high contrast edges.
Marmot, Mount Rainier. Prior to any sharpening.
Ready? Here's how it's done...
First, we'll apply a gentle round of sharpening to the entire image. We'll even go the extra mile and use "luminance sharpening" so that we don't affect any significant color data.
Step 1: Select Layer -> New -> Layer. Give the layer the name "mild global sharpening". Change Mode to "Luminosity".
Step 2: Within the Layers tab, select the Background layer. Next, select Select -> All. Then, Copy the contents of the Background layer and Paste them into your newly created layer. Keep the newly created layer selected for the next step.
Step 3: Select Filter -> Sharpen -> Smart Sharpen. Be conservative. Make use of the Preview option. An Amount of 50% at a Width of .2 pixels should do the trick. Select Remove: Lens Blur and check More Accurate. Click "OK".
Good! We've completed our first pass, global sharpening of the entire image. Next, we will create an edge mask, so that our second pass of sharpening affects only high contrast edges throughout the image.
Step 4: Duplicate the image by selecting Image -> Duplicate
Step 5: Convert the duplicate Image -> Mode -> Grayscale
Step 6: Select Filter -> Stylize -> Find Edges to isolate edges
Step 7: Apply Filter -> Blur -> Gaussian Blur to soften edge transitions. Set Radius at .5 pixels
Step 8: Select Image -> Adjust -> Invert to create your mask.
Step 9: Fine tune mask coverage with Image -> Adjust -> Levels by moving the left-most slider inwards
(Above) A finished mask. Levels adjustment was used to further isolate the marmot from the background.
Excellent! We now have a usable mask. Make the original image active by selecting it from the Window menu. Be sure that your "mild global sharpening" layer, under your Layers tab, is selected.
It's time to load our mask and to apply our second pass of sharpening.
Step 10: Load the edge mask into the orginal image by selecting Select -> Load Selection
Step 11: Select Filter -> Sharpen -> Smart Sharpen. Again, use the Preview option.
Sharpen more aggressively during Step 11, but don't overdo it. Using Filter -> Sharpen -> Smart Sharpen, start with an Amount of 100% at a Width of .2 pixels. Push Amount higher until the image becomes "crispy", then back off slightly. It can take time and practice to find the sweet spot.
HINT: At any time, Ctrl-h (Command-h on Macs) will hide and unhide the current selection or "marching ants".
Voila! Below is our sharpened image.
The image looks pretty good, but did we gain anything over applying simple sharpening to the entire image?
Let's find out.
(Above) Smart Sharpen, Globally, Luminance channel only, 120% at .5 pixels.
Well, this image looks good, too! Was this a waste of time?
I had called out that the creamy background was a priority. I wanted a sharp marmot, but artifact and noise free bokeh. Let's take 100% crops of each image to help us confirm what method is achieving those results.
(Above) Original Image, 100% crop of background
(Above) Sharpening using the two-pass method
(Above) Sharpening using global "Smart Sharpen"
Wow! Look at all of the noise and artifacting in that final crop! Yet, the first two crops are identical! Our two-pass sharpening method maintained a smooth background while providing very effective sharpening of the foreground subject.
In the case of this image, applying a selective, two-pass sharpening methodology to our workflow helped to create a better image than that achieved with global, single-pass sharpening. Of course, there are several ways to modulate what I have accomplished here. You might prefer Unsharpen Mask over Smart Sharpen. Your preference may be to use Curves instead of Levels while fine tuning the edge mask. However you decide to tackle the problem, remember to start by asking yourself questions like:
- What wants to be sharp in the image?
- Where are my areas of high contrast, or, my edges?
- What amount of control is required to preserve and maintain high and low values?
- What areas of the image are susceptible to "noise pollution"?
The answers to these questions will help you to devise an approach to Smarter Sharpening... sharpening for the image at hand!
Jamie, JFP
Questions? Comments? Errors, typos, screwups, doh's, etc? Use the contact form.
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