It would only be copyright infringement if you made copies of the pattern and sold them, either as your own work or just as copies of the designer's work.
That's the whole essence of copy
right -- who has the
right to authorize the sale of
copies. Let's say I write a book. I sell the first publication rights (and maybe other stuff, since they want everything and your firstborn child) to a publisher. You borrow the book from the library and run it through an OCR scanner, then put the whole book up on Amazon for sale at $3 per copy,
none of which comes to me. You have just committed copyright infringement. So what if you put it up on the web to read for free, like a library? Still copyright infringement -- libraries pay for their copies too. Doesn't matter if it's a story or a pattern book. What if you pay me 50 cents from every ebook you sell for $3? Still copyright infringement, with the added bonus that it proves you knew that was my work.
But if you find a pattern either as a stand-alone pattern or in a published book and make changes to it for your own use, it's not copyright infringement. Make it bigger, or smaller, or change the colors from pink and green to red and white. Or use it as a jumping off point for whatever your heart desires. You just can't sell patterns derived from that original -- derivations are protected under copyright as well.
Storytime! I don't know if you recognize the name Margo Rose. She was an American, an inventive quilt designer who made the most imaginative designs, principally in applique. One of her patterns,
an elaborate unicorn, was stolen by someone in Australia who was selling copies as her own work. Margo contacted the thief with a cease-and-desist letter. The thief refused. Margo offered to make her an authorized dealer. Thief refused again. Margo consulted her lawyer, who told her that any copyright infringement lawsuit would have be pursued in Australia in person. And that was when she gave up. Airfare + indefinite hotel stay + cost of an Australian lawyer would cost her far more than her losses from that pattern.
I was in a forum devoted to her work. And when she told us, that was when I got to work. The thief sold her patterns through a website, so I went poking around to see what else she might have. Hm, all sorts of fantasy characters. Oh, look, dwarfs! Isn't it
amazing how much they look like the dwarfs from Disney's
Snow White! Except the pattern instructions said to make them green, for some reason. Maybe the thief believed the false claim that if you change 10% of something, that's enough to make it yours. (Hint: it's not.)
Disney
vigorously pursues copyright infringement. Disney made my local library paint over a mural in their children's section because some of the pictures only looked vaguely like Disney characters. I had an idea that they wouldn't look kindly on Ms. Thief's appropriation of their copyrighted material. So I drew their attention to it and told them how I'd discovered it. I got a very nice email thanking me and that legalities were being pursued. Two weeks later I tried to go back to the thief's website. It was gone.