Core_Computer Studies: Adobe Photoshop Selection tools
Selection tools
The concept of a selection works a bit like a stencil. In Photoshop the area that you select is the area you can work on.
The Rectangular Marquee, the Elliptical Marquee, the Lasso, the Polygon Lasso, the Magnetic Polygon tool, the Single Row, Single Column, and the Magic Wand are selection tools for bitmapped images. “Marching ants”, serve as visual feedback to indicate that an area of an image is selected.
By clicking and dragging the cursor, usually diagonally, over an image when a Rectangular Marquee tool is active selects that area of the image. The Elliptical Marquee, selects an area in the shape of an ellipse, the Single Row selects an area in the shape of a row and the Single Column selects an area in the shape of a column this is a handy tool for removing a thin margin on a bad scan.
The Lasso tool can be used to define freehand selection whereas the Polygon Lasso tool is used to create straight-edged selections by clicking points around an image area.
The Magnetic Lasso tool will automatically detect colour edges in an image and make an outline. A high contrast image with a well defined edge works best. It’s a bit of a trick but click on the edge of a colour and allow the cursor to hover around the edge you want to select. Move the cursor along the edge you want to trace. (You can also drag with the mouse button depressed.)Tolerance values for the Magnetic Lasso tool are found on the Options palette.
The crop tool enables you to select an area to be cropped. After the area has been selected, place the cursor inside the selection and double-click or press Return. The Crop tool options are displayed in the options menu. Specific dimensions and resolution for the cropped area may be set after you check the fixed Target Size check box.
Magic Wand Tool is a tool which selects areas of an image areas based on colour values. To set the Magic Wand’s Tolerance in other words the breadth of the range of colour pixels you will find this in the options bar. Enter a value in pixels, ranging from 0 to 255 (The normal range it is normally set to is 32) Here you can also specify whether the selection should be Antialiased if you want a smooth edge. To select colours that you see using information from all layers that are visible, select “Use All Layers”. Otherwise, the wand tool selects colors from the active layer only.
The options bar
These notes are written for students who undertake the Core Computer course at School of Art, Australian National University. Students of the course should feel free to contact any member of staff with comments questions and general suggestions..
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