LESSON 28 · PHOTOSHOP FOR ARTISTS

A layer mask hides parts of its own layer. A clipping mask uses the layer underneath as a stencil for the layer on top. They sound similar, they are not, and knowing which one to reach for is most of what separates a stack you can still edit tomorrow from one you have to repaint. Adjustment layers finish the set: colour and value changes you can undo six weeks later.

SOFTWARE

Finish first: L7, L8, L26, L27

• The Layers panel and the Properties panel both open
• A brush set to Opacity 100 / Flow 100, hardness around 100%, from Lesson 27
• L28-clipping-practice.psd downloaded

WATCH

PHLEARN — Direct modern equivalent of 'What is a Mask?' (2011). Same concept, current UI, clean education channel.

PHLEARN — L28 is 'Masks, Clipping Masks & Adjustment Layers'. This is a current, focused treatment of adjustment layers plus masking them locally; the 2017 PiXimperfect video predates the current panel layout.

Aaron Rutten — App-agnostic layers primer aimed at beginners, recorded on current software. Aaron Rutten is a clean, tablet-focused digital art educator - a good fit for an XP-Pen course.

THE LESSON

A layer mask belongs to one layer and hides parts of it. You paint the mask in greyscale: white shows the layer, black hides it, mid grey shows it faintly. Nothing is deleted: paint the mask white again and the pixels return.

A clipping mask does not belong to a layer at all; it is a relationship between two. The upper layer is confined to wherever the lower one already has pixels, using that layer's own transparency as the stencil. Repaint the lower layer and everything clipped to it updates instantly.

Rule of thumb: to hide part of a layer, use a layer mask. To paint on top of a shape without going outside it, use a clipping mask. Beginners reach for the eraser in both cases, which works once and then locks the decision in.

Select a layer and click the add-layer-mask button at the bottom of the Layers panel, the rectangle with a circle in it. A white thumbnail appears beside the layer thumbnail; white means everything is visible, which is the sane starting point. Alt/Option-click that button instead and you get a black mask that hides everything, useful when you want to reveal a small area rather than hide a large one.

Click the mask thumbnail to target it, and every brushstroke goes into the mask, not the picture. Press D to load the default black and white into your swatches and X to swap them, and you can hide and restore with one key.

Four moves worth memorising. Alt/Option-click the mask thumbnail to view the mask itself filling the canvas, and again to go back. Press backslash to see it as a red overlay on the artwork instead, which is far better for checking edges. Shift-click the mask thumbnail to switch it off temporarily, marked by a red cross, and Shift-click to restore. Ctrl/Cmd-click it to load its shape as a selection.

The Properties panel adds two dials: Density, which weakens the whole mask without repainting it, and Feather, which softens every edge at once and stays non-destructive. There is also a chain-link icon between the layer and mask thumbnails; while it is there, moving the layer moves the mask too. Click it off to slide artwork behind a fixed mask.

Avoid Layer > Layer Mask > Apply. It bakes the mask into the pixels and throws away everything it was hiding: a destructive move dressed up as tidying.

Paint a flat silhouette of a character's jacket on its own layer. Add a new layer above it and press Ctrl/Cmd+Alt/Option+G, or Alt/Option-click the dividing line between the two layers in the Layers panel. The upper layer indents and shows a small arrow pointing down-left. Now paint as carelessly as you like: every stroke is clipped to the jacket shape, and nothing spills onto the shirt behind.

The real power is that several layers can clip to the same base. On top of one jacket flat you might stack a Multiply layer for shadow, a Soft Light layer for the light across the shoulder, an Overlay layer for fabric texture, and a Normal layer for buttons: four independently editable passes, all obeying the same silhouette. Change it and all four follow.

A lighter alternative is Lock Transparent Pixels, the checkerboard icon in the lock row at the top of the Layers panel. It restricts painting to pixels that already exist on that layer. Quick, and it costs no extra layer, but you paint into the artwork itself, so shading and flat colour end up fused. Use it for a fast colour hold on line art, and clipping masks for anything you might want to change.

One caution: a clipping mask cares only about transparency, not colour or value. If your base layer has soft feathered edges, everything clipped to it inherits them, which is sometimes what you want and sometimes a mystery you spend twenty minutes on.

Click the half-black, half-white circle at the bottom of the Layers panel, or use Layer > New Adjustment Layer. You get a layer that changes how everything beneath it looks without altering a pixel. Double-click its thumbnail later and the same sliders reopen exactly where you left them.

Three earn their place early. Curves is the precise instrument for value: lift the middle of the line for midtones, pull the ends in for contrast, and connect it back to the five-value thinking from Lesson 14. Hue/Saturation shifts, mutes or intensifies colour, and its Colorize option turns a grey painting into a tinted one. Gradient Map maps your darkest values to one colour and your lightest to another, the fastest route from a grayscale study to colour, from Lesson 21.

Every adjustment layer arrives with its own layer mask, and that is where it becomes an artist's tool rather than a photographer's. Paint black into that mask and the adjustment stops acting there. Want cooler shadows only on the left of the face? Add a Color Balance layer and mask everything else.

The mistake to expect: an adjustment layer affects every layer below it, all the way down. To confine it to one layer, clip it with Ctrl/Cmd+Alt/Option+G or the clip button at the bottom-left of the Properties panel. To confine it to a group, put it inside and set the group's blend mode to Normal instead of Pass Through. If an adjustment is changing your background uninvited, that is why.

PRACTICE · 45 MIN

1. Open L28-clipping-practice.psd. It contains flat colour shapes for a simple character bust on four separate layers, plus a line art layer above them.
2. Select the SKIN flat. Add a new layer above it and clip it with Ctrl/Cmd+Alt/Option+G. Set its blend mode to Multiply and name it SHADOW - skin.
3. Paint the shadow shapes on that layer using a mid-warm grey. Deliberately overshoot the edges. Confirm the clipping is catching the overspill.
4. Repeat for the HAIR and JACKET flats: one clipped Multiply layer each, painted carelessly at the edges.
5. Add a clipped Soft Light layer above the SKIN flat for the light side. Two layers, one base, both clipped.
6. Now the layer mask half. Select the JACKET flat itself and add a layer mask. Paint black into the mask to cut a torn edge along the bottom hem. Press backslash to check the edge as a red overlay.
7. Shift-click the mask to disable it, look at the difference, then Shift-click to re-enable it. Nothing was destroyed.
8. Add a Curves adjustment layer at the very top. Raise contrast until the piece reads clearly. Notice it is affecting everything.
9. Add a Hue/Saturation adjustment layer and clip it to the HAIR flat only. Shift the hue. Confirm nothing else changed colour.
10. Add a Color Balance adjustment layer at the top, push the shadows cooler, then paint black into its mask everywhere except the shadow side of the face.
11. Save as a PSD with your own name in the filename. Do not flatten anything.
12. Final test: change the base JACKET flat to a completely different colour. Everything clipped to it should still fit perfectly.

Done when: Your file has at least five clipped layers and two masks, the jacket colour can be swapped in one move without repainting any shading, and the layer names tell you what each one does.

Download these and work along with the lesson.

CHECK YOURSELF

Answer out loud first, then open each one to compare.