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I considered a few algorithms to perform the weave. The first one I devised let me use only @math{(jets-distance_between_jets+1)} nozzles, or 25. This is OK in principle, but it's slower than using all nozzles. By playing around with it some more, I came up with an algorithm that lets me use all of the nozzles, except near the top and bottom of the page.
This still produces some banding, though. Even better quality can be achieved by using multiple nozzles on the same line. How do we do this? In 1440x720 mode, we're printing two output lines at the same vertical position. However, if we want four passes, we have to effectively print each line twice. Actually doing this would increase the density, so what we do is print half the dots on each pass. This produces near-perfect output, and it's far faster than using (pseudo) "MicroWeave".
Yet another complication is how to get near the top and bottom of the page. This algorithm lets us print to within one head width of the top of the page, and a bit more than one head width from the bottom. That leaves a lot of blank space. Doing the weave properly outside of this region is increasingly difficult as we get closer to the edge of the paper; in the interior region, any nozzle can print any line, but near the top and bottom edges, only some nozzles can print. We originally handled this by using the naive way mentioned above near the borders, and switching over to the high quality method in the interior. Unfortunately, this meant that the quality is quite visibly degraded near the top and bottom of the page. We have since devised better algorithms that allow printing to the extreme top and bottom of the region that can physically be printed, with only minimal loss of quality.
Epson does not advertise that the printers can print at the very top of the page, although in practice most of them can. The quality is degraded to some degree, and we have observed that in some cases not all of the dots get printed. Epson may have decided that the degradation in quality is sufficient that printing in that region should not be allowed. That is a valid decision, although we have taken another approach.
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