Knitting machine punchcards are relatively easy to digitize in a way that preserves the information, but relatively difficult to digitize in a way that makes the transition back from stored-on-the-computer to stored-in-physical-material feasible. It is entirely possible to recreate a punch card using an image—by hand, laboriously, with a physical hole punch. (Image: https://archive.org/details/handypunch/ ... s/mode/2up) Usually I work row-by-row, with a ruler across the image, to make sure I’m putting holes in the right spots and chanting things like “3 yes, 1 no, 3 yes, 4 no” in repeating patterns. It is error-prone, but consistent with how generations pre-internet worked with these patterns—translating an image in a book or magazine into binary data of “punch this, not that.”
However, those with more patience for debugging than patience for tedious card-punching have been experimenting with a variety of methods that allow for computer-controlled punching—or, more often, cutting that color correction punching. The Cricut is the standout piece of hardware here, although any machine that can precision cut paper using code will do. These machines, called CNC machines (CNC stands for “computer numerical control”), can have laser or blade attachments, and they work the same way as the massive plasma cutters used for cutting steel. A layer of software, which can be open-source or proprietary, translates an image stored as a SVG (scalable vector graphic) into strings of numbers that control the cutting head.
SVGs aren’t that hard to generate off of images; the challenge here is generating an SVG off an image that actually fits in a punch card knitting machine. There is exactly one spot a hole can go that will work with the dimensions of a knitting machine, and unfortunately, low-quality scans (even pretty-good quality scans) are often too noisy to make it possible to blow up the image and then cut out all the dark spots. I tried, and was rewarded with a punch card that jammed, ripped, and complained loudly for several rows before I gave up. With higher-quality scans, this one-to-one kind of reproduction might work—but only for the machine the punch card was originally designed for. So there’s an incentive to extract the information in those punch cards in a way that is not tied to the specific dimensions of one knitting machine or another. Knitting magazines frequently turned to standardized grid formats for this, preserving the information (“yes, no, yes, yes, no”) but not the specific dimensions of any given punch card.