Selections and Masks

Over the past couple of columns, we've looked at selections and masks, what they are and how they work. This week, we'll explore creating and editing masks by working with the various tools and commands that allow you to take advantage of all 256 levels of "masked."

To start, let's create a practice file that we'll use throughout these exercises. (It will be easier to follow these exercises if you first open the Preferences> Units & Rulers, and set the Ruler unit of measure to pixels.) Open a new Photoshop document, 350 pixels by 350 pixels, 72 pixels per inch, RGB color mode, filled with white. In the Layers palette, click on the New Layer button. Now open the color palette and change your foreground color to R:255, G:255, B:0. Use the Paint Bucket to fill the new layer with this yellow. Next, use Filter> Noise> Add Noise. Use the settings 150%, Uniform, and make sure that Monochromatic is checked. Your image and Layers palette should look like those pictured here.

Next, pop up to the History palette and click on the New Snapshot button at the bottom of the palette to create Snapshot 1. We'll be starting over regularly during these exercises ... but there's no need to got all the way back to a blank file. The History palette should look like this:

For the first exercise, select the elliptical marquee tool in the Toolbox. In the Options Bar (Photoshop 6) or the Options palette (Photoshop 5 & 5.5), set Feather to 0 and uncheck the anti-alias option. Elect the Constrained Aspect Ratio option and make sure that it is set to Height 1, Width 1.

Drag a circular selection. With the rulers visible, I dragged from 50,50 to 300,300. You don't need to be precise any circular selection that covers a large area of the canvas is fine. Now press Q on the keyboard or click the Quick Mask Mode button at the bottom of the Toolbox. In Quick Mask mode, the image should look like this:

You see that the selection has defined a mask. The mask has crisp, sharp edges, as seen by the definite break between the red overlay and the unprotected area of the image. A close-up:

If you zoomed in, return to 100% zoom. Exit Quick Mask mode by pressing Q on the keyboard or clicking the Standard Mode button in the Toolbox. Use the command Select> Deselect or press Command-D (Mac) or Control-D (Win). Go to the Options Bar or palette and add feathering to the Elliptical Marquee. Type in 25 (or, if your unit of measure for the rulers is not pixels, type in 25 px). Drag the same circular marquee as in the previous example. Again, enter Quick Mask mode. Your new mask should appear similar to that shown here:

We'll zoom in to 500% again. Compare the earlier zoom with this one. Notice, first, that rather than a sharp, clean division between masked and unmasked, the red overlay fades. Looking at the rulers visible in each image, you'll see that the same area of the canvas is shown.

If we return to 100% view, exit Quick Mask mode, and hit Delete, the selection's feathering (shown in the mask as the gradual fade) results in partial deletion of some pixels.

Now that the relationship between selections and masks has been reinforced, let's make some masks from scratch. In the History palette, click on Snapshot 1 to return the image to the state seen above in the first figure. (You should have two layers, one filled with yellow with added noise.)

Enter Quick Mask mode. Press D on the keyboard or use the icon in the Toolbox to return your colors to black and white. Select the Gradient tool and, in the Options Bar or palette, choose a black-to-white linear gradient. Drag the gradient from left to right. You'll create a mask similar to the one shown by the red overlay here:

Exit Quick Mask mode and look at the resulting selection. Observe that it seems to encompass only half of the image. The pixels contained within the selection marquee are selected at least 50% - whatever filter or command is applied will be at least 50% effective on those pixels. Let's see what happens when we hit Delete.

Note that, like the feathering seen earlier, the deletion is only partially applied to some pixels.
Return to Snapshot 1 in the History palette and enter Quick Mask mode again. Use the Lasso tool to drag a selection. With the foreground color still set to black, use the Paint Bucket to fill the selection. Drag the Eraser tool across the middle of the selection. The mask may (or may not) look similar to this:

Exit Quick Mask mode and hit Delete. You'll get an image comparable to this:

Again, click on Snapshot 1 in the History palette and enter Quick Mask mode. Use the Paint Bucket to fill the image with the red overlay. Apply the command Filter Render> Clouds. Exit Quick Mask mode and hit Delete. Your clouds are likely to differ from these, but the general idea is the same - the filter was applied to the mask, changing the way in which the mask created a selection.

Snapshot 1; Quick Mask mode - back to our original test image. Use the Paint Bucket to fill the image with a mask. Next, Filter> Noise> Add Noise. The settings should still be those we used earlier. Click OK. Filter> Blur> Motion Blur. Set the angle to 0 degrees and the distance to 9 pixels. Click OK. Filter> Stylize> Emboss. The Angle can be 135 degrees, the Height should be about 10 pixels, and the Amount can be set to 300%. Click OK. Exit Quick Mask mode and hit Delete. Press Command-H (Mac) or Control-H (Win) to hide the edges of the selection to get a better look at the result.

Press Command-Z (Control-Z) to Undo. (Remember that the selection edges are hidden but the selection remains active.) Apply Filter> Blur> Motion Blur, using the settings Angle: 34 degrees, Distance: 30 pixels. Notice that the areas outside the selection borders are untouched, while the Motion Blur has been applied with varying effect in the rest of the image.

Return yet again to Snapshot 1 and enter Quick Mask mode. Use the Paint Bucket, with the foreground color still set to black, to fill the image. Filter> Stylize> Tiles is what we'll use next. Set the number of tiles to 10, the maximum offset to 10%, and elect to fill with the background color. Click OK. Next, head for Filter> Sketch> Bas Relief. The setting should be Detail: 7, Smoothness: 5, with the light coming from the top left. Click OK. Exit Quick Mask mode. Choose Filter> Pixelate> Crystallize. Pick a cell size of 50. Click OK.

Hide the edges with Command-H (Control-H), and notice how, yet again, the mask has protected some areas, while allowing the rest of the image to be filtered.