Monday, August 20, 2007
Essential Processing Techniques
Tools all photographers should know for adjusting exposure, color and sharpening
By Harlon Mitchell
Photoshop Unsharp Mask And Smart Sharpen
Two of the best sharpening tools in Photoshop CS2 and CS3 are Unsharp Mask and Smart Sharpen. They offer the most control over how an image is sharpened and how much is applied.
Unsharp Mask adjusts the contrast of edge detail by slightly lightening and darkening the pixels on either side of an edge. This emphasizes all the edges and creates the illusion of a sharper image. Three sliders let you adjust sharpening: Amount, Radius (how many pixels are affected along the edges) and Threshold (a sensitivity control that basically tells the sharpening algorithm to only change pixel detail and contrast beyond the level you set).
The Smart Sharpen filter gives you even more control. One of three sharpening algorithms can be used: Remove Gaussian Blur, Lens Blur or Motion Blur. Remove Gaussian Blur is the method used by Unsharp Mask. Remove Lens Blur detects the edges and detail in an image for finer sharpening and reduced halos, while Remove Motion Blur helps reduce blurring caused by camera or subject movement when using slower shutter speeds.
You select Amount and Radius, or go to the advanced mode and adjust the sharpening of dark and light areas separately in the Shadow and Highlight tabs. Fade amount determines how much sharpening will be applied; tonal width controls the range of tones to be modified.
Aperture's Sharpening Tools
The tools to know in Aperture are Sharpen and Edge Sharpen. Sharpen has two sliders for setting intensity and pixel radius, and Edge Sharpen has three sliders for setting the intensity, edges and falloff.
The Intensity slider controls the amount of sharpening. The Edges slider lets you set the number of pixels that qualify as edges to be sharpened, and the Falloff slider controls the amount of sharpening applied on each of the three passes across the image.
For the best results, Apple recommends setting the falloff parameter to a value between 0.4 and 0.7. A value of 0.7, for example, means 70 percent of the sharpening set on the Intensity slider will be applied on the first pass, with progressively less of that 70 percent applied on each of the next two passes that further refine the sharpening already done. Total sharpening by the three passes always adds up to the value set on the Intensity slider.
The filter is also unique in that typical sharpeners work in the RGB color space, which can cause unusual colors to appear when sharpening is applied. Aperture's Edge Sharpen works on luminance information of the image and leaves the hue and saturation of the colors alone.
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