This needlepoint I'm working on came in the form of a kit containing yarn and a printed canvas. It's possible to do needlepoint without a printed canvas by working from a chart. It would be considered counted needlepoint and I've done some pillows this way. I've also done a pillow working from a photograph of a pillow without the chart. The resolution was just good enough for me to see the distinct stitches.
Another alternative is hand painted canvas and they are expensive--needless to say. I've never worked from a hand painted canvas but I imagine they are very accurate. Accuracy is sometimes lost in printed canvas and I suspect it's especially true of a large canvas like the one I'm working. The printing process needs to lay down the correct color at the intersection of two canvas threads and if the registration is off at all or if the canvas slips, or whatever else I know not, the color can end up straddling a space instead of covering an intersection.
When I come across this in the canvas I simply decide--by looking at the overall pattern and neighboring areas--whether to move the color up or down, and always within the same area, move the colors consistently in one direction.
This picture shows colors out of alignment. The canvas intersections are half yellow and half another color. I have to decide whether to move the colors up or down:
If the printing went askew at the borders, the line between the design and the border could be jeopardized, ending up jarred--broken between two different rows and this will 1) be very obvious and 2) look like a mistake. This picture shows how the bottom edge of the pattern goes astray:
Looking at the right arrow shows that the last row of the wide border comes up to the green border. If we keep the bottom of the design on the same row--which we must if we want to avoid something that looks like a mistake--then by the time we get to the left arrow, we see the printing alignment gradually going off and eventually the top of the green border is a whole row lower than it was on the right.
This happened at the top of the canvas as well. I am having to make adjustments by dropping the last line of the design as it floats away from the current line (see bottom circle below). It will become part of the green border.
Since there is a solid double line above the wide border as well (top circle below), I've had to improvise here as well. If you follow the two red arrows at the top, going from the right to the left you can see that the line would be broken if I kept to the misaligned printing, and since I don't want that I'm dropping a line above the border and adding one below it. I'm making up the pattern for this row as I go along, pointed to by the blue arrow, ignoring what's printed and basing it on what the design is doing. (According to the canvas this would be the bottom row of the double line, but I've had to keep the double line higher to avoid it skipping down a row.) The wide border pattern is quite abstract so it's pretty hard to go astray, just about anything works.
By the way. . . I'm at the bottom!!! Can't believe it. Will be done soon. But I have to order some yarn and will have to wait for it to arrive before I can really finish it.