Sheen

Sheen grew up in the deep river-gorge, where the sun only reached the bottom for one hour a day, always slanting in from the same eastern lip of rock. Her family were potters, and they'd learned something the flatland potters never had to: down in the gorge, you could only tell one pot from another by its shadow. A bowl and a plate looked identical from the top. But when the one-hour sun came slanting in from the east, the bowl threw a deep curved shadow inside itself and the plate threw almost none — and suddenly you could see the shape of each, carved out by that single, reliable, one-directional light.

Little Sheen used to sit and wait for the sun-hour just to watch the pots turn round. "Same clay, same glaze," her father said, turning a bowl slowly, "but the light tells the truth about its shape — as long as the light stays put." When a visiting potter once lit lamps all around a bowl to "show it off," the bowl went flat and confusing, lit from everywhere and therefore from nowhere. Sheen never forgot it: too many lights is the same as no light. It's the one honest direction that lets a shape be seen. She carried the unlit lantern from that day on, to remind herself to choose.

At twelve Sheen climbed out of the gorge and walked to PixelForge, brass lantern swinging on its stick. Palette met her at the door.

"What is light source and form shading?"

Sheen raised her lantern and aimed it at the doorframe. "It's making a flat shape look round," she said, "by choosing where the light comes from and keeping that choice. I pick one direction — say the light's up and to the left. Then the bright pixels go on the up-left side of everything, and the shadow pixels go on the down-right side of everything, all through the picture. One light for the whole scene. If I light each thing its own way, nothing looks solid. It's the one kept direction that turns stickers into round things."

Palette looked at the cat whose two ears already told the story — one bright, one dim. "You've been shading yourself your whole life," she said.

"I grew up somewhere with only one hour of honest light," said Sheen. "It taught me not to waste it."

"You're the one," Palette said, and the warm studio light fell across them both from a single high window.

Sheen's workshop had one big window and no other lamps, on purpose. On her table sat the unlit lantern and a glowing canvas, and today Sumi the otter-kit was scowling at a picture of a red apple. The apple was a perfect red circle. It was also completely flat — a red coin, a sticker, a hole punched in the screen.

"It won't look like an apple," Sumi complained. "It's just a red circle. I colored it in really neatly and it's still flat."

"Neat and flat," Sheen agreed, not unkindly. "Because it has no light. Let's give it one — just one." She lifted the lantern and aimed it at the top-left corner of the canvas. "The light lives there. Now everything obeys." On the top-left curve of the apple she placed a few pixels of pale, bright red — almost pink — where the imaginary sun would strike. On the bottom-right curve she placed a few pixels of deep, cool red — nearly maroon — where the sun couldn't reach. Between them she let Shade's ramp do the rest, mid-red curving around the form.

"Step back," she said.

Sumi stepped back and made a small startled sound. The coin was gone. A round apple sat on the screen, bulging toward the light, curving away into shadow — solid enough to pick up.

"You didn't redraw it," Sumi said.

"I chose a light and obeyed it," said Sheen. She showed the little otter the rules, one lantern-aim at a time. Pick the light direction first, before you shade a single pixel, and write it on a sticky note if you have to. Highlights always on the lit side, shadows always on the far side — for every object, the same way. Don't light the apple from the left and the leaf from the right; that's the lamps-everywhere mistake, and it makes a scene go flat and dizzy. And keep the highlight small and the shadow honest — a shape gets round through a few bright pixels and a few dark ones, not by coloring the whole thing brighter.

"One thing to be steady about," Sheen said, "and the whole picture lines up behind it."