(Picture from the Met Museum)
By zooming in on these pictures, you can actually count the stitches. For example, below is a zoomed in picture of the green embroidery pictured above. For every dark spot on the thread line, that would be a stitch.
Here is another page from the same book:
Below is a zoomed in picture of the page from above. Just like with the green thread, you can count the dark spots on the brown thread line to count the stitches that create the pattern.