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Sharpen images with Edge Selection Mask
- How to do it
- Open Channels Palette
- Use Find Edges Filter to define the image edges
- Use Levels to heighten contrast
- Smooth out edges of
Alpha Channel - Apply Levels Again
- Invert the Alpha Channel
- Convert to a mask
- Optimize JPEG image for
Web by using the mask - 421 image files
- Work licensed under Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License
CIS 421 › Photoshop > Sharpen with an Edge Selection
Sharpen images with Edge Selection Mask
An edge selection mask lets you sharpen up image edges with more control than the Unsharp mask Filter.
Sometimes this technique helps bring up a faded image or one without sharp outlines
How to do it
Open the Channels palette
- Choose the color channel with the best edge pattern
- Drag that color channel into the Create New Channel icon at the bottom of the Channels Palette to create a channel to use as a mask
Use Find Edges Filter to define the image edges
- With the new color channel selected, click Filter>Stylize>Find Edges, which will automatically trace the edges of the image
- reveals black lines on white background
- Click Image>Adjustments>Invert to invert the selection
- changes to white lines on black background
Use Levels to heighten the contrast
- Press <control> L to open the Levels palette
- Drag the top-left (shadow) slider and top-right (highlight) slider toward the middle.
- This will get rid of the weaker edges & strengthen the stronger edges.
Smooth out edges of the Alpha Channel
- Click Filter>Blur>Gaussian Blur
- Enter radius of about "2" pixels
Apply Levels Again
- Press <control> L to open the Levels palette
- Drag the top-left and top-right sliders together again to leave just the most important lines.
Invert the Alpha Channel
- Press <Control> I to0 invert the channel so that the black lines become white lines
Convert to a mask
- Click the Load Channel as Section button (leftmost button at bottom of channels palette) to create an edge mask.
- Click the eye next to the RGB channel in the channels palette to see the marching ants of the selection.
- Press <control>H to hide the selection so you can see the results
- Click Filter>Sharpen>Unsharp mask
- Slide the Amount slider far to the right
Optimize JPEG image for the Web by using the mask
- Select>Deselect to remove selection
- Click File>Save for Web
- Choose the 2-up display to see the Optimized version that Photoshop has created
- If you do not see a JPEG image, click the JPG in the dropdown box in the right part of the window
- Reduce the file dimensions in the Image Size Window to a percentage (say 50%) of the original
- Click the 4-up display to see the Optimized version and 2 others in the lower cells of the window
- Click the image in the lower left part of the window to select it
- Set the quality to the same level as the optimized version
- Click the mask icon next to the quality setting in the right window
- Select the edge mask you created in the Channel dropdown list
- Click OK
- You can see the differences in file size and image quality by looking in the two versions in the Save for Web window.