LESSON 27 · PHOTOSHOP FOR ARTISTS

Opacity and Flow look like the same slider and are not, and getting them backwards is the single most common reason a beginner's digital painting looks plastic. This lesson takes the brush engine apart: where pressure enters, where it goes, and how to set it up so you are not squashing the nib all day. Then you build one brush from nothing and keep it.

SOFTWARE

Finish first: L3, L6, L26

• Your saved painting workspace from Lesson 26
• Brush Settings and Brushes panels both open
• The XP-Pen driver open in a second window so you can reach the pressure curve

WATCH

Ctrl+Paint — The clearest four minutes on the internet about the setting most beginners get backwards. Watch this before you read anything else.

Ctrl+Paint — How to get full-strength strokes without pressing hard. This matters more than it sounds when the tablet is new and your hand is still learning.

Adobe Photoshop — Adobe's own walkthrough of turning a drawn mark into a brush tip. Short, exact, and it matches the practice below step for step.

THE LESSON

Both live in the options bar when the Brush tool is active, both are percentages, and they do completely different jobs.

Opacity sets the maximum darkness one continuous stroke can reach. Put the pen down at 40% opacity and scribble over the same spot fifty times without lifting: the mark stays at 40%. Everything between pen-down and pen-up is one stroke, and it cannot pass the ceiling. Lift and go again and you are at roughly 64%, then 78%, each pass stacking on the last.

Flow controls how much paint leaves the brush at each instant. At 20% flow with opacity at 100%, a slow stroke that overlaps itself does build up, because each moment of contact adds another thin layer toward the ceiling. That is why flow feels like real media and opacity feels like a stamp.

For painting, use Opacity 100 and Flow between 10 and 30, controlling value by how many passes you make and how hard you press, the way you already work with a pencil. For inking, use Opacity 100 and Flow 100: a line either exists or it does not. The number keys set opacity and Shift plus a number sets flow.

Beside them is the airbrush toggle, or Build-up: with it on, flow accumulates while the pen is held still. Leave it off until you want that.

Your X4 stylus reports 16,384 pressure levels and 60 degrees of tilt, but Photoshop only uses that data where you tell it to, in the Brush Settings panel's left-hand list.

Shape Dynamics is where pressure becomes size. Tick the box beside the words, not just the words, then set Size Jitter's Control to Pen Pressure. Below it, Minimum Diameter is the thinnest the brush may get at the lightest touch: near zero for tapered inking lines, 20 or 30 percent for a brush that varies but never disappears.

Transfer is where pressure becomes opacity and flow. Same rule: tick the checkbox. Set Opacity Jitter's Control to Pen Pressure for a brush that darkens as you lean in, or Flow Jitter's Control to Pen Pressure for something more like a soft pencil. Both at once is usually too much.

Give each brush one main job for pressure. An inking brush uses pressure for size only, opacity locked solid. A painting brush uses pressure for flow, size fixed and driven by the bracket keys or a dial. A brush where pressure runs size, opacity and flow at once is mush, and you cannot tell which variable made the mark you liked.

One trap worth knowing before it costs you an hour: the options bar holds two pen-shaped toggle buttons, one for always using pressure for size, one for opacity. They override the brush's own settings. If a brush suddenly ignores your Shape Dynamics, or will not paint solid black, check those two first.

Watch the Ctrl+Paint video above before you touch this. The problem it describes is real: if full opacity only arrives at maximum pressure, you press hard all day. Knuckles ache, your fingertip goes white, nibs wear fast, and you build a heavy grip you then have to unlearn.

The fix lives in two places. First, the XP-Pen driver's pressure curve, from Lesson 3: pull the curve up and to the left so light and medium pressure already produce high output. Your pen activates at about 2 grams and reports over sixteen thousand levels, so there is enormous resolution at the light end. Use it.

Second, lower the flow instead of leaning harder. A brush at 15% flow reaches solid colour in four gentle passes; at 100% flow with a punishing curve it gets there in one crushing press. Same pixel value, and only one of them lets you draw for two hours.

Take the physical warning signs seriously: a sore first knuckle, a white fingertip, squeaking on the glass, chewing through nibs. There are ten spare nibs in the box; if you are into your third in a month, the curve is wrong, not you.

Custom brushes are less mysterious than they look. A brush tip is just a greyscale image: black deposits full paint, white deposits nothing, greys deposit partially. That is the entire secret.

Make a new document with a white background, paint a mark in black, and choose Edit > Define Brush Preset. Name it and it appears at the bottom of the Brushes panel. A charcoal smudge, dry-brush streaks, a cluster of dots, three overlapping leaf shapes: all become brushes.

That is only the tip. In Brush Settings, Brush Tip Shape holds Spacing, which decides how far apart the stamps land: the default 25% leaves visible dots on a textured tip, so drop it to 1 to 10 percent for a continuous stroke. Then add Shape Dynamics with Angle Jitter's Control set to Direction if you want the tip to rotate along your stroke, which makes a flat chisel tip behave like a real one.

Now save it properly. Define Brush Preset stores the tip shape alone. To keep spacing, dynamics, size and blend mode together, use the new-brush button at the bottom of the Brushes panel and include tool settings. Otherwise you reload it next week and wonder why it feels wrong.

Do not build a library. Two good brushes beat forty downloaded ones: you learn what a brush does by using it for months, not by scrolling a list.

PRACTICE · 40 MIN

1. Open L27-flow-vs-opacity-grid.psd. There are eight empty boxes with printed labels.
2. Box 1: Opacity 100, Flow 100. Make one slow S-stroke that crosses over itself twice.
3. Box 2: Opacity 30, Flow 100. Same stroke, without lifting the pen. Note that the crossings do not darken.
4. Box 3: Opacity 100, Flow 15. Same stroke. Note that the crossings do darken.
5. Box 4: Opacity 30, Flow 15. Same stroke, then repeat it four times lifting the pen between each.
6. Boxes 5 to 8: repeat boxes 1 to 4 with the airbrush toggle switched on, pausing for two seconds at the middle of each stroke.
7. Write one sentence under the grid, in your own words, describing when you would use box 3.
8. Now open the Brush Settings panel. Turn Shape Dynamics on, set Size Jitter Control to Pen Pressure, and set Minimum Diameter to 0. Draw ten tapered lines in the strip at the bottom of the file.
9. Turn Shape Dynamics off and turn Transfer on with Opacity Jitter Control set to Pen Pressure. Draw ten more lines in the same strip. Compare the two rows.
10. Open L27-brush-tip-source.psd. Pick one of the three marks, select it with the Rectangular Marquee, and use Edit > Define Brush Preset.
11. Set the new brush's Spacing to 5%, add Shape Dynamics with Size Jitter on Pen Pressure, and add Angle Jitter with Control set to Direction.
12. Save it as a new brush preset from the Brushes panel, including tool settings, and name it with your initials so you can find it later.
13. Paint one small object with only that brush. No other brush allowed.

Done when: Your grid file shows eight visibly different results, you can explain the difference between box 2 and box 3 out loud, and you have one saved custom brush that survives a restart of Photoshop.

Download these and work along with the lesson.

CHECK YOURSELF

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