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Lecture 3

Computer Science 1033A/B Lecture Notes - Lecture 3: Decontamination, Nondestructive Testing, Acne Vulgaris


Department
Computer Science
Course Code
COMPSCI 1033A/B
Professor
Vivi Tryphonopoulos
Lecture
3

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Image Manipulation 4/20/2013 6:47:00 PM
Lecture 3
Masks
Why Use Masks?
o Instead of deleting a background, swap it with another one
o Allows you to manipulate specific parts of an image (colour of
hair, shirt, tilt head, etc.)
o Masks are an easier alternative to the eraser tool
o Tilt-shift photography placing the focus on a subject in the
foreground while blurring out the background & vice versa
Gives the impression of a miniature model
Choose photos with elevated viewpoints
E.g. buildings, roads, traffic and railways
o Gradient tool go gently from colour to black and white
How it works:
o Use selection tool to select the part you want to change
don’t need to be exact
o Create a mask based on the selection
The selected area can be altered
o The area outside/around the selection is protected from
change
This part is masked (protected from editing)
How to use masks:
o Step 1 you have 2 layers
You have a background scene and a model
Make sure you are on the layer of the model
Choose whether or not to make a selection
Click “Add Layer Mask” icon
o Step 2 select or don’t select?
If select:
Use selection tool to select outline of person
Add a Layer Mask to the layer
Layer mask is filled with black and white***
Creates a black mask
If don’t select:
Add a Layer Mask to the layer

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Layer mask is filled with white***
Creates a white mask
Why is one mask filled with b/w and the other white?
Black conceals, white reveals***
A black mask hides everything on that layer
A white mask shows everything on that layer
o Step 3 brush tool to paint pixels
Brush with the foreground color:
Black removes areas you want to hide
White brings back areas you want visible
Grey controls opacity
Black mask (conceals) paint with white to make pixels
visible again (white foreground)
White mask (shows everything) paint with black to
make pixels disappear (black foreground)
Advantages of masks:
o Pixels are NOT removed permanently
o They are hidden or made visible
o You can remove/add effortlessly swapping between
black/white
o You “mask” pixels, don’t eliminate them
o If you mask pixels, you can replace them at any time during
the same session or another session
Eraser comparison:
o Once pixels are removed they're permanently gone
o Limited with undo/step backwards
o Can’t close the file and get it back with undo options
Types of Masks
Refine mask gains accuracy around edges of a mask
o Smart Radius automates the selection to refine rough edges
o Paint around the edges great for fine details like hair
o Smooth smooth out the jagged edges
o Contrast making the edge stronger
o Shift edge pulling in or pulling out
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o Decontaminate colours helps the edges blend in more with
what is surrounding it
Clipping mask an object or group of objects whose shape masks
other artwork so that only areas that lie within the clipping mask
are visible
o Allows you to texturize the look using another photo
o You are clipping the artwork to conform to the shape of the
object (or mask)
o It must be above the mask in the layer panel***
o Can be letters or shapes
Quick mask allows you to make a selection
o You are NOT creating a mask, you are entering a mode
o Quick mask is a way to make a selection with the paint
brush***
Similar to selection tools like marquee and lasso
Paint the area that becomes your selection
o How to create a quick mask:
Enter Quick Mask Mode
Use the brush to paint over the selection you want
creates a red overlay
Exit Quick Mask (press Q) the marching ants appear
o Defaults when in quick mask mode:
Foreground Black (if white, it removes the red
overlay, whats already painted)
Background White (un-paints, like previously stated)
Color overlay Red (and transparent) indicates masked
areas
You are saying what you don’t want as part of your
selection***
Thus you have to check “Selected Areas” in quick
mask options
What you paint is the actual selection (what you
will be adjusting)
Opacity setting: leave as 50% so that you can see
what is below in what you are painting
o Correct errors in painting:
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