Figure 5

First, go to the Layers palette and select a layer containing a color that you want to replace with dots. Then drag that layer onto the Create A New Layer button in the Layers palette to make a copy of it. Now hide the copied layer and reselect the layer that you just copied. Choose Filter > Pixelate > Color Halftone. In the resulting dialog box, shown in Figure 6, adjust the Max. Radius setting to a number between 4 and 127. Click OK. Keep in mind that the larger the number, the larger your dots will be.

Figure 6

Your color fill should now resemble that shown in Figure 7. At this point if you like the results you can leave your image as it is, but if you want to adjust the coloring of the dots, you can.

Figure 7

To change the appearance of your dots, select the copied version of your layer and make it visible. Then set the layer's blending mode to Screen, as illustrated in Figure 8.

Figure 8

Note: The results of changing the layer's blending mode are subject to change depending on the original color of your image. To get the final effect that you're looking for you may have to test out a few of the different blending modes offered in the Layers palette.

Now, simply repeat this step on any other parts of your image that you want to add dots to, until you're happy with the way the entire piece looks.