Eraser

• The easiest way of filling with transparency is by using the "Eraser" tool. Click the tool palette icon shaped like an eraser, then drag over the image region you want to fill with transparency. Unless the "Layers" window indicates the current layer is called "Background," the regions you drag over will fill with a checkerboard pattern. This pattern is Photoshop's default method for indicating transparency.
  
  

Background

• If you are trying to use "Eraser" to fill a region on the "Background" layer with transparency, your mouse strokes will reveal the background color, not transparency. To change this behavior, double click the "Background" item in the "Layers" window. Photoshop will display a dialog box prompting you to enter a name for a new layer that will replace "Background," and whose image content will be the same as "Background." Click the dialog box's "OK" button to accept the default name, which will have "Layer" in its preface. Or, type a descriptive name such as "ErasableLayer." Photoshop will change the "Background" layer to one whose images you can fill with transparency rather than the background color.
  
  

Use Selections for Accuracy

• Using the "Eraser" tool to fill a region with transparency requires you to zoom in closely if you want to be exact in the region you're filling. By contrast, if you define a region before using "Eraser" to fill it, you can use broad strokes of your mouse at any zoom level. To define an image region, use one of Photoshop's many selection tools, including "Rectangular" and "Elliptical marquee," or the "Magic wand" selection tool. For example, if you want to fill a circle having a single, uniform color with transparency, click the tool palette icon shaped like a magic wand, then click the circle. Photoshop will seek the edges of the shape by looking for colors that don't match those of the shape. This behavior relieves you from having to meticulously and slowly drag the mouse cursor around the circle's outline.
  
  

Cut and Delete

• Photoshop's intuitive "Eraser" tool isn't the only way of filling an image region with transparency. The program's "Cut" and "Delete" functions can also perform this kind of fill. To run either of these functions, first use a selection tool like "Rectangular Marquee" to define the region to fill. Then press "Control" and "X" simultaneously, or press "Delete." as long as the layer from which you'd deleting is not the "Background" layer, your keypress will complete the transparency fill. If you are working in the "Background" layer, first convert it to a regular layer by double clicking "Background" in the "Layers" window, then clicking "OK." Repeat the "Control" and "X" or "Delete" keypress just mentioned to make the region transparent.