What a mask is

A mask is a black-and-white visibility map attached to a layer. The pixels of the drawing do not change. The mask only decides which of them to show. This is called nondestructive editing: you can undo the decision even an hour later.

A laptop on a wooden table

Black hides, white shows

The logic is simple. Where the mask is white, the layer is fully visible. Where it is black, the layer is hidden. Gray gives partial transparency: 50% gray hides half the layer. You can paint on a mask with any brush. Switch the color from black to white, and the same tool both hides and brings back.

Why it beats the eraser

The eraser deletes pixels for good, and after twenty steps of history you cannot get them back. A mask keeps the whole drawing.

The layer mask

This is the most flexible kind of mask. It attaches to one layer and controls only that layer's visibility, without touching its neighbors.

Soft transitions with gray

A soft brush at 20–30% opacity paints a clean gradient on the mask. That is a good way to fade the edge of fog, smoke, or the distant part of a landscape. Pass twice over the same spot and the transparency builds up, so the transition goes deeper. For hard edges, use a hard brush at 100%.

Bringing back what you hid

Hid too much? Switch the color to white and paint the spot back. Nothing is lost, and you do not need the undo history. A shortcut for flipping black and white is in the collection of keyboard shortcuts for artists.

Check

If you cannot tell what the mask is doing, view the mask itself instead of the drawing. In most editors, click the mask thumbnail while holding a key. You will see a black-and-white map and spot right away where a transition is too harsh.

The clipping mask

A clipping mask works differently: one layer is clipped to the shape of another. The upper layer is visible only where the lower layer has pixels.

Shadow that stays inside the shape

Fill a hand silhouette on its own layer. Above it, create a layer and clip it as a clipping mask. Now paint the shadow with a wide brush in broad strokes. It will not leave the silhouette. The work goes about twice as fast, because you do not have to be careful at the edges.

Texture that follows the silhouette

The same move works for texture. Need a plaid on a dress? Draw it on the clipped layer, and it is cut to the shape automatically. Then set that layer to Multiply, from the guide to blend modes, and the plaid will sit with the folds.

Alpha lock

Alpha lock stops you from painting on the transparent parts of a layer. The brush works only where pixels already exist.

Recolor an object fast

Turn on alpha lock on a layer with a filled object and paint over it in a new color. The shape stays exact, down to the pixel, including soft edges. It is just as handy for tinting line art: a black outline becomes a warm brown in a minute.

How it differs from a mask

The difference is flexibility. Alpha lock turns on with one button, but it is tied to the layer's current contents. A mask takes more setup, and you can edit it on its own.

Practice on one object

The theory sticks when you run it on a real piece. Take a simple character from the waist up and go through the whole path.

A character: skin, clothes, and light

  1. Fill the character silhouette with one color on its own layer.
  2. Above it, add a layer with the local colors of skin, hair, and clothes.
  3. Clip that layer as a clipping mask, so everything stays inside the silhouette.
  4. Create a shadow layer in Multiply, clipped the same way.
  5. Add a highlight layer in Screen at 50% opacity.
  6. Put a mask on the background layer and softly fade its edges.

The setup scales easily to complex illustrations. It helps most in clean graphics, for example in line art and minimalism, where any slip at the edge is obvious.

Check the edges

Zoom the drawing to 200–300% and walk the outline of the object. Look for two problems: a semi-transparent fringe from a soft brush, and white gaps between the fill and the line. Alpha lock with a hard brush fixes the fringe. Extending the fill by 1–2 pixels under the line closes the gaps.

Time to draw, not just read

Theory fades in a couple of days if you never use it. Open the editor and spend 15 minutes on what you just read. That is enough for the skill to stick.

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Topics in this guide

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