Jamie explained why he was getting frustrated.

“That’s what I hate about this task — the notes don’t tell us everything we need to know. I don’t know what this bit means, so I don’t want to put anything down that’s too specific. I hate that. I’m just that kind of person; I want things to be… correct.” He sighed. “It’s taking a long time.”

“I know what you mean,” I said. I paused to think. “Have you ever saved a JPEG file in Photoshop before?”

“No.”

“You get two options. You can save it normally, or as an interlaced JPEG. When you load these up on a webpage, the normal JPEG loads up line by line. You see the picture come up and it takes a while but each bit is perfect.

“The interlaced JPEG is different. It loads up, say, every fifth line. Then it goes back and fills the next set of lines. So you see the whole image, fuzzy at first, but then it becomes clear — and you end up with exactly the same picture as the normal JPEG in the same amount of time.”

I stopped. “Do you see what I mean?” I ended, unable to finish the story I had started.

“Yes,” Jamie said immediately. “Different ways to work.”

“Yes,” I said in delight. “If we work like interlaced JPEGs, we draw the outline then roughly fill in some details. It’s not perfect yet but we have vague idea what it might look like. The beauty of interlaced JPEGs is that at some point, you might decide that you’ve seen enough — you don’t need to download the whole thing. So you stop the browser.”

“So being interlacers is more flexible,” Jamie said thoughtfully. “You can stop when you’ve achieved what you needed to.”

“And you can stop before you go too far down the wrong path.”

He had decided. “Well, Joan, let’s you and I be interlacers.”