Masks can be defined to invalidate pixels either outside or inside a region. A mask is created by specifying a collection of mask primitives. Primitives are combined using logical operators to determine the overall effect of the mask on a specific location. Commands regarding mask creation and modification can be found under the Masks menu item. Masking also uses the mask toolbar:
Mask Primitives
Three types of mask primitives are supported in Phase MOSAIC:
| Circle | Center and radius are specified. |
| Polygon | A series of connected vertices are specified. |
| Ellipse | Center, major and minor semi-axes, and position angle are specified. |
Defining Masks
| Create | Select one of the primitive buttons before clicking and dragging on the view window to generate a mask primitive with default characteristics. | |||||||||||||||
| Load | Previously stored masks can be retrieved and added
to the existing collection of mask primitives. The  button can also be used. | |||||||||||||||
| Clear | Removes all defined mask primitives. The  button can
also be used. | |||||||||||||||
| Save | Stores the currently defined mask to disk. The  button can also
be used. | |||||||||||||||
| Modify by mouse | Mask primitives can be modified by clicking and dragging either the drag handle or mask boundary of a mask primitive. | |||||||||||||||
| Modify by dialog | Mask primitives can also be modified by right-clicking a drag handle or mask boundary and selecting the Properties menu item. Parameters relating to the selected mask primitive can be specified. | |||||||||||||||
| Overlay Mode | Each mask primitive combines with previous
primitives using an overlay mode. This is a logical operator used to determine the overall
mask state at a particular location. The mask state at a particular position can be
thought of as the result of a sequential equation involving each primitive's state and
its' overlay mode as the operator. The primitive's overlay mode can be changed by
right-clicking a drag handle or mask boundary and selecting the Properties
menu item. Use the combo box to select the appropriate mode. A table of choices and their
results is given below:
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| Clipboard Operations | Mask primitives can be cut or copied to the clipboard by right-clicking a drag handle or mask boundary and selecting the Cut or Copy menu item. Mask primitives stored in the clipboard can be pasted to the view by right-clicking any other point and selecting Paste Mask Element. |
Applying the Mask
Minimum Version
Full Version
| Remove | Mask | Allow the currently defined mask to change the
pixel data. Pixels in masked regions are made non-valid. The  button can
also be used. If the mask is no longer needed, it can then be cleared. |