Advanced Layers

As we discovered in Layer Basics, the key to keeping your editing flexible while easily combining images together is through layer masks. Let’s take a moment and review how masking works in Photoshop as it will apply to more complex features through out this tip and technique. The only rule to remember is that painting with black in a mask will hide whatever is on the layer, revealing the layers below. Painting with white will reveal the information on the layer, hiding the layers below. In this image, there are two layers, the ocean (which is the Background) and the “cracked earth”. We’ll add a Layer Mask to composite them together. With the “cracked earth” layer targeted in the Layers palette, select Layer > Add Layer Mask > Reveal All.

To paint in the mask, from the tool box, select the paintbrush, choose black as the foreground color and from the options bar, select a soft edge brush. The softness of the edge will help to create a subtle transition in the mask between the cracked earth and the water. Begin painting in the mask with black to hide the unwanted areas of the “cracked earth” layer. Shortcut: hitting the “d” key will set the foreground and background colors to their default (black and white).

If, by accident, too much of the layer becomes hidden because you painted in areas of the mask with black that shouldn’t have been, paint with white in the “mistake” areas to reveal the layer again. Typically I set the background and foreground colors to their defaults when working with masks, then I can just swap the foreground and background colors by clicking on the double headed arrow to exchange between black and white. Shortcut: hitting the “x” key will exchange the foreground and background colors.

The most common problem when first using layer masks is forgetting (or not knowing) that it makes a difference if the layer or the layer mask is targeted. If the layer mask is targeted, then painting affects what is hidden or revealed by the mask, if the layer is targeted, painting will replace the information on the layer. To target the Layer mask, on the Layers palette, click on the thumbnail for the Layer mask. When the mask is targeted, a small mask icon appears in the Layers palette between the eyeball and the layer thumbnail. The Layer Mask thumbnail also gains a one pixel black outline around it (this is very subtle).

To manipulate the layer, the layer thumbnail (not the layer mask thumbnail) must be targeted. When the layer is targeted, a small paintbrush icon appears between the eyeball and the layer thumbnail. The layer thumbnail also gains a one pixel black outline around it (again, this is very subtle). A good rule of thumb to follow is when painting on a mask, if the results aren’t what were expected, stop painting, and look at the layers palette. Confirm that the correct layer is targeted, that the Layer Mask is targeted, and that the mask icon between the eye and the layer thumbnail is showing.

This brings us to an important concept of layer masks. If painting with black in a layer mask hides the information on the layer, and painting with white reveals the information, then shades of gray can be used to partially hide or reveal information. To demonstrate, I added a layer containing an image of clouds and added a mask by selecting Layer > Add Layer Mask > Reveal All. To acheive an even transition between the horizon and the new clouds, I selected the Gradient tool, choose the black to white gradient with the linear option, and dragged the gradient from slightly below the horizon upwards. The Gradient tool created a smooth transition from black to white over the distance of the line drawn. The clouds image was hidden by varrying levels of opacity created by the graduated mask. Note: the longer the distance between start and end point of the gradient, the slower the transition.

By default, the layer and the layer mask are linked together so that if you move or transform the layer, both the mask and image are altered. However, between the layer thumbnail and the Layer Mask thumbnail, there is a link icon. Clicking on this links and unlinks the mask to the layer so that they can be transformed and repositioned individually. This feature can be particularily useful if the mask is positioned correctly but the layer isn’t or, if you want to transform a layer to fit within a mask. In this example unlinking the mask from the layer and targeting the layer thumbnail allows me to reposition the clouds with the Move tool without moving the mask.