Lecture 3 - Image Manipulation.docx

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Western University
Computer Science
Computer Science 1033A/B
Vivi Tryphonopoulos

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  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 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 –
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