Aperture: Tips on Using Edge Sharpen in Aperture 1.5

Basics

The Edge Sharpen adjustment in Aperture is a professional tool that's used to sharpen photos. Unlike some sharpeners, Edge Sharpen has four special characteristics:

• Only edges are sharpened
  Edge Sharpen computes an edge mask and uses it to constrain the results of the sharpening operation. This means that, with the right settings, you should be able to sharpen your image without bringing up the texture in the noise, or in the sky. This can be useful in sharpening the edges of a face without introducing pockmarks.

• Only image luminance is sharpened
  Typical sharpeners work in the RGB color space. This can cause unusual colors to appear. So Edge Sharpen performs its sharpening only on the luminance information of the image, leaving the hue and saturation alone.

• Image luminance is sharpened in a perceptual space
  Sharpening should be accomplished in a space that has equal steps for equal perceptual steps. The Aperture Edge Sharpen adjustment does this so that the sharpening effect will be approximately the same in shadow areas as it is in the midtones.

• Three sharpening passes are employed
  

  It has often been mentioned on professional photography sites that typical sharpening algorithms can be improved by using several small sharpening steps with lower intensity. Usually the visual improvement is a decrease in the "ringing" around hard edges. These three sharpening passes are accomplished at different pixel radii (you can think of them as 1, 2, and 4 pixels, although their exact radii, actually standard deviations, are slightly different). Also, each sharpening pass uses a lowered intensity to purposefully avoid excessive "ringing" around edges. The relative contributions of each sharpening pass can be controlled using the Falloff slider.

Note: The 1, 2, and 4 scales were chosen specifically because they straddle the typical sharpening radius for a digital camera image (2.2 pixels).

Parameters

You can control Edge Sharpen to get professional results.

Intensity
The Intensity slider controls the overall amount of sharpening applied. Drag the Intensity slider to the right to increase the amount of sharpening applied to the image, and drag the Intensity slider back to the left to reduce it.

Edges
The Edges slider controls which pixels are edges and which are not. Drag the Edges slider to the right to increase the number of pixels that qualify as edges, and drag the Edges slider back to the left to restrict sharpening further. If you see noise increasing in a flat area of the image, like the sky, decrease the Edges parameter value.

Falloff
The Falloff slider controls how much sharpening is applied during the three sharpening passes at 1, 2, and 4 pixels respectively. Usually, the most sharpening happens in the 1-pixel pass, less in the 2-pixel pass, and less still in the 4-pixel pass. Drag the Falloff slider to the right to equalize the amount of sharpening power between the three sharpening radii, and drag the Falloff slider back to the left to increase the total sharpening power proportionately at the smallest features. Typically you should set the falloff parameter to a value between 0.4 and 0.7; a value of 0.7 means that, proportionately, only 70 percent of the sharpening power applied at the 1-pixel scale is applied at the 2-pixel scale, and only 49 percent of the 1-pixel scale sharpening is applied at the 4-pixel scale. Note that total intensity (between the three passes) always adds up to the indicated value of the Intensity slider.

Workflow

To sharpen an image:

1. Set the Intensity slider to the maximum value to see the effect of the operation.
2. Adjust the Edges slider so you can see which parts of the image are being sharpened. If possible, adjust the Edges slider so that edges are sharpened, but noise and texture in the image are not affected.
3. Adjust the Falloff slider so that the edge sizes you want sharpened the most are accentuated.
4. Decrease the Intensity parameter value until the sharpening effect is appropriately subtle. Usually a value of 0.5 is too much.

Edge Sharpen and RAW Edge Sharpening

You can control the amount of sharpening applied in the RAW demosaic process as well. It is controlled by the Intensity and Edges sliders in the RAW Fine Tuning adjustment. This sharpening is generally applied to all your RAW files, so you might want to turn it down (or off) and apply sharpening as an adjustment later. If you want sharpening applied automatically as part of your RAW workflow, leave the settings at the default values. They are intended to "undo" the effect of the camera's internal anti-aliasing filter and provide a suitably sharp image right out of RAW conversion.