Photoshop comes with various selections tools you could utilize to specify what region of an image you want to manipulate. Once you have a selection area defined using these tools, the software will preserve all pixel information outside the selected region. Selection tools are compatible with each other regardless of their corresponding operations, thus, you could create pixel precise selection regions via any number of steps to define the region itself.
You can find the selection tools right under the Move tool in the toolbox. By default, Photoshop gives you the Rectangular Marquee Tool – hotkey: m – which lets you define a rectangular selection region. The simplest selection you could create in Photoshop is to define a custom rectangular shape with the Rectangular Marquee Tool, though it also is the method to define an area that you want to keep from an image. With a document of your choosing opened, go ahead and designate an area of the document using a rectangular selection. Now try using manipulative tools like a Brush or even Filters on the image. You will see that pixels outside this simple selection will not be affected by the actions you perform, but pixels inside the selection region will be manipulated.
In case you want to define an area of an image that you want to keep without the rest of it, first create the desired selection using the Rectangular Marquee Tool. Now go to Image – > Crop. The picture is restructured and now you are free to deactivate the selection by going to Select – > Deselect, or by relying on the hotkey combination of the same command: „CTRL + d”.
As you have just seen, the Rectangular Marquee Tool gives you a method to define rectangular selections with custom proportions to the shape. In case you need to constrain these proportions to be a mathematically precise rectangle though, you could rely on the SHIFT modifier key after you started to define the region. Go ahead and draw a column or a row with the Rectangular Marquee Tool, but do not release the mouse button. Instead, hold down SHIFT while still pressing the mouse. As you will see, the proportions will be constrained to a precise rectangle and will maintan this shape as long as the modifier key is pressed.
Additional Selection Modifiers with the left mouse button pressed
There are additional hotkeys you could rely on whenever you define a selection region. The most important thing to keep in mind is to keep the left mouse button pressed until you are happy with the selection. Once you release the button, the current selection will be amended and you will not be able to customize it without adding to- or subsrtacting from it. As long as you keep the mouse button pressed down though, additional modifiers could be invoked.
In the previous example, you constrained a rectangular selection region to maintain the shape of a mathematically precise rectangle, by using the SHIFT modifier key without releasing the mouse button. Now try the SPACE modifier with the mouse button pressed: this hotkey will let you translate the active selection region on both axes. Now give a try to the ALT modifier: this hotkey will set the pivot point of the selection to its center, giving you a whole different method to generate the selection by. The best aspect of these modifier keys is that they are stackable on each other. They will not interfere with each other at all and will remember their corresponding functions even if invoked simultaneously.
Additional Selection Modifiers without the left mouse button pressed
Once you are happy with the current state of the selection, you can release the mouse button, thus amending the selection state. This is where the creation of more complex selections may start from, according to the current need. Once you have created the region, do not change the Rectangular Marquee Tool. Press and hold down the SHIFT modifier once again, instead. As you will see, the cursor will show a tiny “+” sign as long as you keep the modifier key pressed, indicating that a consecutive selection with the Rectangular Marquee Tool will add pixels to the selection area. Now press and hold down the ALT modifier. The cursor will display a tiny “-“ sign, indicating that a consecutive selection will subtract from the region.
Finer Shapes, Finer Selections
You have seen how to generate rectangular selections and how to manipulate those by relying on various modifier keys. To make the selection regions as fine as possible though, you need to be able to define elliptical and even free form regions. Photoshop gives you all these tools and the techniques you have just learned are all compatible with them. To access these tools, click on the tiny arrow on the right side of the Rectangular Marquee Tool’s icon, or press right click on it. This will give you access to the other selection tools that are components of this particular tool group: the Elliptical Marquee Tool and the Single Row- and Single Column Marquee Tools.
The Lasso Tool, right below the Marquee Tools, also comes in different variants. The Lasso Tool lets you define free form selection regions. Its two additional variants, the Polygonal Lasso Tool and the Magnetic Lasso Tool are valuable companions with a similar aim. The Polygonal Lasso Tool will let you define an area using straight lines. Once you are happy with the selection, press ENTER to amend it. In case you want to step backward to a previous point, use BACKSPACE.
The Magnetic Lasso Tool has contrast sensitivity, thus it will do a fairly nice automatic job of guessing what you may want to select. Using these straightforward selection tools and their universal modifier keys, complex manual selections could be made.