Stumper

To a soften the edge between a selection and surrounding pixels, we use the option “Feather”.
To use this option, we have a number of possibilities.
One possibility is to use the “Feather” box that we find in the options bar at the top, when a selection tool is selected (1).
A second possibility is to first make a selection, then the “Select” button in the menu bar, choose “Modify” in the drop-down menu, and click on “Feather”. This opens a dialog box (2) where you type in a value for the “Feather Radius”.

A third possibility is to first make a selection, the “Select” button in the menu bar and select “Refine Edge” in the drop-down menu.
In the “Feather” (1), give a value for the feather radius.
More about dialog “Refine Edge” in the next Lesson, because this is much improved in CS5.
For your information:
the option “Show Original” is the opposite of the previous “Preview” option.
If this is selected, you will see only the selected in the example and when this is not selected, you see no example.

When you drag the selected example to a different image, you will notice that the cover-up perfectly equal to the obfuscation that we got to see in the preview.

 

Anti-alias

When we make a selection, we usually find the “Anti-Alias” option in the top option bar. What this option does is, it makes the edges of the selected area smoother.

To clarify this, I have two selections, One for alias and other for anti-alias and make them selection with channels.

For this, I click the “Save Selection as Channel” button (1) at bottom of “Channels” panel.

When you zoom-in the picture and view with the alpha channel (2), you can clearly see the difference between the Anti-alias and the Alias.
Alias gives a more coarse selection, while Anti-aliasing has a more smoother transition between the selected and unselected.
FYI, the black pixels in the alpha channel are not the selected pixels, but the white pixels are selected pixels.
The “Alias” selected area has only black and white pixels, while the “Anti-alias” selected area also has pixels with different gray values.
It is these gray values, which ensures the smooth transition.
The lighter the gray value, the more transparent the pixel.

FYI.
When you view the alpha channel of a selection where you are “stumped”, you will see that there are several differences in the gray values.

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