• Marching ants
  • Only shows pixels that are more than 50% selected. Not a good way to evaluate partially selected pixels
  • command-h: hides ants (but you still have the selection)
  
  
• Quick mask mode: press "Q" or the quick-mask icon in the tool bar
  • Shows all pixels that are selected. (includes pixels that are less than 50% selected).
  • You can paint in/out selection using any painting tool when in Quick Mask mode
    • Note the difference when you use a hard-edge brush and a fuzzy brush
  • Make sure you go out of quick mask mode as some tools will not work (eg. selection).
  
  
  
• Layer Mask
  • \ ("backslash") to display current layermask
  • or "option click" on layermask
  
  
  
• Quick Mask == Selections == Layer Masks

To convert a layer mask to a selection:

• Right click on the layer mask
• Select Add Mask To Selection
  
  
  
  
  

To convert a selection (marching ants) into a layer mask

• After you make the selection, hit the "Add Layer Mask" button (located at the bottom of the layers panel).
  
  
  
  
  
• Or, Edit -> Fill into the layer mask.

• select -> {border, modify, smooth, expand, contract}
  
  
• Another way to expand/contract selection
  • Make a duplicate layer of the image+hard-edged layer mask
  • Gaussian blur ( 0.5 - 1 pixel) the layer mask
  • Levels: gamma slider (midpoint) controls expantion/contraction
  • This works only when your edges are consistant (eg. all hard-edged) to begin with.

• Vector based selection using the pen tool
• Based on color using Color Range (Finder -> select -> color range).

Without partially selected pixels, the selected areas will have crisp, jagged edges. But most photographic images don't have crisp edges.

For graphics/fonts, a technique called anti-aliasing is used:

• Anti-aliased
  
  
• No Antialiasing
  
  
  
  

1. Use a selection tool (for example, Quick selection) and make a quick (hard edged) selection.
2. Create a layer mask based on that selection
3. Open the Masks Panel (if you don't see it double click on the layer mask
   
   • Density: controls transparency of the mask
   • Feather: blurs the layer mask. Hard edged to soft edge.
     
     
   
   

This video starts with out a selection. I prefer to start off with a selection to make available to myself the full selection tools before I go into this utility.