Step 12: Add A Layer Mask To The Background Copy Layer

Switch back over to your main document and make sure the Background copy layer is selected in the Layers panel. Click on the Add Layer Mask icon at the bottom of the Layers panel:

Again, nothing will seem to have happened in the document, but a white-filled layer mask thumbnail appears on the Background copy layer in the Layers panel, letting us know that we've added the layer mask. Notice that the thumbnail has a thin highlight border around it. This tells us that the layer mask itself is selected:

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Step 13: Fill The Layer Mask With The Circle Pattern

Once again go up to the Edit menu at the top of the screen and choose Fill. This time, change the Use option from Black to Pattern:

Click on the Custom Pattern preview thumbnail to select the pattern you want to use:

This opens the Pattern Picker. Choose the circle pattern we just created by clicking on its thumbnail. It should be the last thumbnail in the list. If you have Tool Tips enabled in Photoshop's Preferences, the name of the pattern will appear when you hover your mouse cursor over the thumbnail:

Click OK once you've selected your pattern to close out of the Fill dialog box. Photoshop fills the layer mask with the circle pattern, and our image is now made up of a pattern of colored dots:

I'll zoom in closer to the image so we can see the effect more easily. Each dot in the image is made up of a single solid color thanks to the Mosaic filter we applied earlier. The black area surrounding the circles is from Layer 1 below the image (which we filled with black back in Step 3):

Step 14: Add A Hue/Saturation Adjustment Layer (Optional)

As an optional final step, we can enhance the effect a little by increasing color saturation in the image. Click on the New Adjustment Layer icon at the bottom of the Layers panel:

Choose a Hue/Saturation adjustment layer from the list that appears:

If you're using Photoshop CS3 or earlier, a Hue/Saturation dialog box will pop open on the screen. For Photoshop CS4 and CS5 users, the controls for the Hue/Saturation adjustment layer will appear in the Adjustments panel. In either case, increase the color saturation in the image by clicking on the Saturation slider and dragging it towards the right. The further you drag to the right, the more saturated the colors will become. I'm going to increase my saturation to +20:

For Photoshop CS3 and earlier users, click OK to close out of the Hue/Saturation dialog box. Photoshop CS4 and CS5 users can leave the Adjustments panel open. And with that, we're done! Here, after boosting color saturation, is my final "photo to colored dots" result:

And there we have it!