Smart Photoshop Selections Pixel-Perfect Image Acquisition Helen Bradley
Wed 5/15/02 -- In Adobe Photoshop as in most things, there are usually two ways of performing a task: the easy way and the hard way. The outcome is the same; the only differences are the time you spend and your level of frustration. So unless you're in the happy position of charging by the hour (for a client with deep pockets), the easy method is the way to go.
Making selections -- picking portions of an image to copy, mask, or perform other Photoshop functions -- is a prime example. The best method is the quickest one for the job you're doing, so here are my best tips for making fast and accurate selections every time.
Adding, subtracting, and overlapping. You aren't committed to using any one of the lasso selection tools; in fact, it's easy to change between them. To select a shape with some straight lines and some curved, for example, use the Polygon Lasso tool to draw around the regular-shaped area, then switch to the Lasso tool (while you're still working with the selection) by holding the Alt key.
You can also create complex shapes by adding selections together -- simply hold the Shift key as you draw the second and subsequent selections. To subtract the second selection from the first (say, to make a donut by removing the hole from a circle), press Alt as you draw the second (the smaller circle). To choose only the area common to two selections, press Alt-Shift as you draw the second selection. (Click on thumbnail at right for full-sized screen shot.)
Moving a selection. Remember the donut? If, when you're selecting the smaller circle, you find it's drawn in the wrong place, you can hold the space bar and move it into position. When you release the space bar, you can continue to draw the selection (if required). While this technique seems a little fiddly at first, it's a neat trick for tweaking selections, particularly when you're working with more than one at a time.
Selecting to size. To make a fixed-size selection -- for instance, a 100 by 50-pixel rectangle for a Web page thumbnail -- choose the Marquee tool. From the Style dropdown list, choose Fixed Size and set the width and height. When you draw the selection on the image, it will be the exact dimensions you've chosen. Alternately, if you just want a fixed aspect ratio (in this case, 2:1 width to height), choose the Constrained Aspect Ratio option, set the width and height values, draw your shape.
Shift and shift again. You probably already know how valuable the Shift and Alt keys are when making new selections. The former key constrains an ellipse to a circle; a rectangle to a square; and, with the Polygonal Lasso tool, constrains the lines to positions which are multiples of 45 degrees.
The Alt key, used with the Rectangular or Elliptical Marquee tool, lets you to draw from the center of the shape outwards. So what if you want to add a circle to a circle? To do this, you must overcome the fact that the Shift key's primary function is to add two selections together and not to create the second selection as a circle. The solution is to press Shift, then start to draw the second ellipse (this adds it), then let go of Shift, click it again, and drag to form the circle.
Skewing a selection. Any Photoshop selection can be skewed or deformed if you choose Select/Transform Selection. Handles appear which you can drag to alter the selection's shape. You can also rotate it, or distort it by holding the Ctrl key as you drag any handle.
Selections to go. It's often handy to store a selection along with an image file -- for example, a shape to use for Web buttons. To do this, make your selection and choose Select/Save Selection and type a name for it. You can later choose Select/Load Selection to load the selection into the same image. You can also add it to any other open image (provided they have the same pixel dimensions) if you choose Select/Load Selection from inside the image within which you want to use the selection. If the images aren't the same size, load the selection into the first image, open the second image, and simply drag the selection from one to the other.
Fine-tune a selection by painting. Make your selection, then click the Edit in Quick Mask Mode button to apply the mask. You can now paint to add to the masked area or use the Eraser tool to remove the mask. When you're done, choose Edit in Standard Mode to create a selection from the mask and return to your image. (Click on thumbnail at right for full-sized screen shot.)
