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Note: Photoshop CS2 tools and menus are used here as examples which may be different from other image editing programs.
 

Sharpening images

Sharpening enhances the definition of edges in an image. Whether your images come from a digital camera or a scanner, most images require some sharpening. Keep in mind that sharpening cannot correct a severely blurred image.

Quick tips

  1. Sharpen your image on a separate layer so that you can resharpen it later if you need to do so.

  2. If you sharpen your image on a separate layer, set the layer’s blending mode to Luminance to avoid color shifts along edges.

  3. Sharpening increases image contrast. Use the layer blending controls to prevent sharpening in highlights and shadows.

  4. If you need to reduce image noise, do this before sharpening.

  5. Sharpen your image multiple times in small amounts. Sharpen the first time to correct blur caused by capturing your image. After you’ve color corrected and sized your image, sharpen it again

  6. For greatest control use the Unsharp Mask filter or the Smart Sharpen (Photoshop CS 2) filter to sharpen your images. Although Photoshop also has the Sharpen, Sharpen Edges, and Sharpen More filter options, these filters are automatic and do not provide controls and options.

To use the Smart Sharpen filter

The Smart Sharpen filter has sharpening controls not available with the Unsharp Mask filter. You can set the sharpening algorithm or control the amount of sharpening that occurs in shadow and highlight areas.

1- Zoom the document window to 100% to get an accurate view of the sharpening.

2- Choose Filter > Sharpen > Smart Sharpen.

3- Set the controls in the Sharpen tabs:

  1. Amount sets the amount of sharpening. A higher value increases the contrast between edge pixels, giving the appearance of greater sharpness.

  2. Radius determines the number of pixels surrounding the edge pixels affected by the sharpening. The greater the radius value, the wider the edge effects and the more obvious the sharpening.
    Remove sets the sharpening algorithm used to sharpen the image.

  3. Gaussian Blur is the method used by the Unsharp Mask filter.

  4. Lens Blur detects the edges and detail in an image, and provides finer sharpening of detail and reduced sharpening halos.

  5. Motion Blur attempts to reduce the effects of blur due to camera or subject movement. Set the
    Angle control if you choose Motion Blur.

  6. Angle sets the direction of motion for the Motion Blur option of the Remove control.

  7. More Accurate processes the file longer for a more accurate removal of blurring.

4- Adjust sharpening of dark and light areas using in the Shadow and Highlight tabs. If the dark or light sharpening halos appear too strong you can reduce them with these controls:

Fade Amount adjusts the amount of sharpening in the highlights or shadows.
Tonal Width controls the range of tones in the shadows or highlights that are modified. Move the slider to the left or right to decrease or increase the Tonal Width value. Smaller values restrict the adjustments to only the darker regions for shadow correction and only the lighter regions for highlight correction.
Radius controls the size of the area around each pixel that is used to determine whether a pixel is in the shadows or highlights. Moving the slider to the left specifies a smaller area, and moving it to the right specifies a larger area.

5- You're done. Click OK.

The Unsharp Mask filter
 


Before Unsharp Mask
After Unsharp Mask

 
The Unsharp Mask sharpens an image by increasing contrast along the edges in an image. The Unsharp Mask does not detect edges in an image. Instead, it locates pixels that differ in value from surrounding pixels by the threshold you specify. It then increases the contrast of neighboring pixels by the amount you specify. So, for neighboring pixels the lighter pixels get lighter and the darker pixels get darker.

In addition, you specify the radius of the region to which each pixel is compared. The greater the radius, the larger the edge effects. The effects of the Unsharp Mask filter are more pronounced on-screen than in high-resolution output. If your final destination is print, experiment to determine what settings work best for your image.

To sharpen a photo using Unsharp Mask

1- If your image is multilayered, select the layer containing the image you want to sharpen. You can apply Unsharp Mask to only one layer at a time, even if layers are linked or grouped. You can merge the layers before applying the Unsharp Mask filter.

2- Choose Filter > Sharpen > Unsharp Mask. Make sure the Preview option is selected. Click the image in the preview window and hold down the mouse to see how the image looks without the sharpening. Drag in the preview window to see different parts of the image, and click + or – to zoom in or out.
3- Drag the Radius slider or enter a value to determine the number of pixels surrounding the edge pixels that affect the sharpening. The greater the radius value, the wider the edge effects. And the wider the edge effects, the more obvious the sharpening.

The Radius value varies according to the subject matter, the size of the final reproduction, and the output method. For high-resolution images, a Radius value between 1 and 2 is usually recommended. A lower value sharpens only the edge pixels, whereas a higher value sharpens a wider band of pixels. This effect is much less noticeable in print than on-screen, because a 2-pixel radius represents a smaller area in a high-resolution printed image.

4- Drag the Amount slider or enter a value to determine how much to increase the contrast of pixels. For high resolution printed images, an amount between 150% and 200% is usually recommended.

5- Drag the Threshold slider or enter a value to determine how different the sharpened pixels must be from the surrounding area before they are considered edge pixels and sharpened by the filter. For instance, a threshold of 4 affects all pixels that have tonal values that differ by a value or 4 or more, on a scale of 0 to 255. So, if adjacent pixels have tonal values of 128 and 129, they are not affected. To avoid introducing noise or posterization (in images with flesh tones, for example), use an edge mask or try experimenting with Threshold values between 2 and 20. The default Threshold value (0) sharpens all pixels in the image If applying Unsharp Mask makes already bright colors appear overly saturated, choose Edit > Fade Unsharp Mask and choose Luminosity from the Mode menu.

Selective sharpening

You can sharpen parts of your image by using a mask or a selection. This is useful when you want to prevent sharpening in certain parts of your image. For example, you can use an edge mask with the Unsharp Mask filter on a portrait to sharpen the eyes, mouth, nose, and outline of the head, but not the texture of the skin. Using an edge mask to apply the Unsharp Mask only to specific features in an image.

To sharpen a selection

1- With the image layer selected in the Layers palette, draw a selection.
2- Choose Filter > Sharpen > Unsharp Mask. Adjust the options and click OK.

Only the selection is sharpened, leaving the rest of the image untouched.

To sharpen an image using an edge mask

1- Create a mask to apply sharpening selectively.
Open the Channels palette and select the channel that displays the grayscale image with the greatest contrast in the document window. Often, this is the green or the red channel.

Selecting a channel with the greatest contrast

Duplicate the selected channel.

  1. With the duplicate channel selected, choose Filter > Stylize > Find Edges.

  2. Choose Image > Adjustments > Invert to invert the image.

  3. Find Edges filter applied and image inverted

  4. With the inverted image still selected, choose Filter > Other > Maximum. Set the radius to a low number and click OK to thicken the edges and randomize the pixels.

  5. Choose Filter > Noise > Median. Set the radius to a low number and click OK. This averages the neighboring pixels.

  6. Choose Image > Adjustment > Levels and set the black point high to get rid of random pixels. If necessary, you can also paint with black to retouch the final edge mask.

  7. Setting the black point high in Levels to eliminate random pixels in the edge mask

  8. Choose Filter > Blur > Gaussian Blur to feather the edges.

3- In the Layers palette, select the image layer. Make sure the selection is still visible on the image.
4- Choose Select > Inverse.
5- With the selection active on the image layer, choose Filter > Sharpen > Unsharp Mask. Set the desired options and click OK.

Plug-in

Focus Magic



Focus Magic consists of a set of image restoration filters which can focus (sharpen) an image which is blurred Although there are many image editing programs with a “Sharpen” or “Unsharp Mask” feature, none come anywhere close to the re-focusing capabilities of Focus Magic. Unsharp Mask and Sharpen filters simply increase the contrast at the edges of an image. This amplifies the noise or grain in an image, and can only be applied a little before the colors start to look un-natural. Focus Magic uses “deconvolution” which uses advanced mathematics to reverse the process by which the image got out of focus.

Focus Magic can also defocus (soften) an image. An image can be defocused by varying amounts. You can also  increase the resolution of an image which has too few pixels to print with smooth edges. The Increase Resolution filter uses ground breaking technology to get rid of the pixelized look of images which have a low resolution.

To use Focus Magic,  set the image source. The “Image Source” optimizes the focusing algorithm for that particular source. The focusing algorithm is more conservative for sources which are less accurate and is more aggressive for sources which are more accurate. Non-linearities are also taken into account for photographic film and CCD’s. The difference to the output is quite small, but worth it if you know what the image source is.

In order to focus an image, Focus Magic needs to know the amount by which the image is out of focus. This is specified by the ‘Blur Width’ and is the distance that an edge has spread (in pixels). When you open an image, Focus Magic auto-detects the Blur Width, but it is advisable to experiment a little. Simply click on an area that you want to focus. Focus Magic will focus that small area using the current filter settings. Adjust the ‘Blur Width’ up or down until you get the best result. Changing the ‘Blur Width’, automatically updates the preview. Repeat the process for a few different parts of the image.

Once you have determined the most suitable ‘Blur Width’, select the most appropriate Focus Amount. This is normally set to 100%, but you can tell Focus Magic to “Under Compensate” or “Over Compensate” with Amounts which are less that 100% or greater than 100% respectively.


Once you have done some spot checks on the image you can press the OK button to focus the whole image. There is a huge amount of number crunching to do, which can take from a few minutes to over an hour for a very large image. Focus Magic has been designed to run in the background, so provided you are not running low on memory, you can use your computer for something else while the image is being focused.