Author Topic: Selective Sharpening  (Read 2082 times)

keithsnell

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Selective Sharpening
« on: February 08, 2009, 05:16:31 PM »
When I saw Todd Obiedo's image of a grasshopper on a wild onion, I commented that it was a great image, but might benefit from a little "selective sharpening" of the grasshopper. 

Todd asked if I could describe the process for selective sharpening.  Since I often mention selective sharpening in my discussions on image processing, I thought it might be worthwhile to provide a quick tutorial on the subject.

I should mention that many applications contain tools (such as an adjustment or selection brush) to simplify this process, including the new Camera Raw included with Photoshop CS4, Lightroom 2.0, and Capture NX2.  Using these "brush" tools, you can selectively "paint" sharpening to selected parts of your image.  The following tutorial is a slightly less automated way that uses layer masks to accomplish the same effect using previous versions of Photoshop.

We'll start by adding a "duplicate layer."  We will perform all of or sharpening actions on this duplicate layer, apply a mask, and then "paint" through the mask to show only the areas of the image that we want sharpened.  To add the duplicate layer, view the Layers Palette (Window>Layers), right click on the background layer and select "duplicate layer."


In the pop-up dialog box, type a name for your new layer.  I've chosen to name the layer "selective sharpen" so I can keep track of what changes I've made in the future.


Now we're going to apply "smart sharpening" to this layer.  Under the filter menu select "Sharpen" then "Smart Sharpen."


Ensure the "preview" box is checked so you can preview the results of your selected parameters.  For this image, I've chosen an amount of 200%, radius of 1 pixel, and selected "remove lens blur" in the drop down menu.  I should caution that this is a VERY aggressive amount of sharpening, and this much sharpening would be way too much for most images.  I played with the sliders a bit while previewing the changes, and decided I would use these agressive settings in order to get a sharp eye on the grasshopper.   


Much of the image did look over-sharpened, so this is where we add our layer mask to "hide" the sharpening, and then "paint" through this mask with a brush to allow only selected parts of this sharpened layer to show through to the final image.  (When using masks, black will hide the selected portions of the layer, while white will allow those portions of the layer to show through.)


Once you have added your layer mask using the "hide all" option, select a soft edged brush (set "hardness" to zero), ensure you have selected white as your foreground color (click on the color squares on your tool palette to select your foreground color), and begin painting on the mask in the areas where you want the sharpening to show through.  You will be able to see these changes on your on-screen image as you "paint" in the sharpening.


You can see the areas on the mask where I have "painted" white, and the corresponding areas on the image that are sharpened.  (Head, thorax and leg of the grasshopper.)


I decided the area of the grasshoppers wing just in front of the leg looked over-sharpened, and so selected a "gray" color and painted over that area to reduce the amount of sharpening that would "show through" from this layer into the final composite image.


Here's the final result:


Hopefully this helps you understand the concept of "selective sharpening" and gives you one possible method for performing selective sharpening on your images.  You might want to practice on a few images of your own, and then ask questions if you have any.

Keith



« Last Edit: March 10, 2009, 02:21:37 PM by keithsnell »