Hey great stuff. There's a couple of things I can see here. Maybe useful, maybe not.

1. Blurred image. This is where sample area might be set quite high in relation to the size of the grid. When sample area is 1, then the density of the shaded patch is controlled by the colour of one single bitmap pixel in the centre of the patch. This often leads to very contrasty, chequerboard kinds of patterns, so increase sample area a little. Increasing this means the sample area is increased, and the density of the pixel ends up as an average of a larger area - naturally you'll lose sharp detail.

2 & 3. Pen size and grid size. Our old adversaries. You have a fairly small grid size, with a fairly large, and bleedy pen. Looking at the pen width test, the most dense pixel is the one where the pen is set to 0.4mm, and that has only got 8 waves in it. So with that sized pen and grid, there's really only 7 different densities that can be expressed.

With the pensize set to 0.8, it'll be even fewer than 8 densities, and I guess the bleedy pen might not help.

4. Gaps between your rows. Either you've got pixel scaling turned down a little, or you can pull your pen in a bit until just the very tip is extended out from the gondola, and the stabiliser is almost flat against the page. When the pen sticks out, pulling on the cords tends to move the gondola, but not necessarily the pen tip. That might hel with the bleed too, since the tip will not stay still for as long.

Some solutions:
Edit your image so the shadows are brightened. Use the curves tool to keep the black black, but the shadows are much closer to the midtones. Careful, a simple brightness adjustment will blow out the highlights. Notice the back of the hand has already been blown out - this is just because of the low range of the gridsize+pensize combination.

Use a smaller pen, or even set your pen tip to a smaller setting. The pen width test let you know that only when the pen was set to 0.4 was the pixel entirely coloured in. Reducing the pen size from 0.8 (I think I read right that's what you were using). That said, on the drawing, the darkest pixels look pretty dark to me - maybe I misunderstood what you did.

Remember you can select small panels to draw rather than the whole thing. I usually select specific features I want to make sure get expressed, and draw and redraw just that little sub-panel until I get the settings dialled in just right.

Looking pretty good though - but you do have some pretty fine material to work with.

sn

Ha! Sandy beat me again.

The pen width test draws a series of solid pixels, maximum density, but changes the pen size for each pixel. It ignores your current actual pen size entirely. The purpose of it is to help you decide what you want your darkest pixel to look like. A side-effect is that it measures the width of the line that your pen produces.

You started with pen size 0.4, then went to 0.6, then 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6.

So the first pixel is filled in with the pen tip size set to 0.4mm. With that sized pen, it looks like you can fit in about 8 waves, so it draws 8 waves (maximum density for that thickness of line).

The second pixel is 0.4+0.2=0.6. With a pen this size, you can't fit in as many waves, so maximum density only draws about 5 or 6 waves So 6 is the maximum density for that thickness of line.

The third pixel is 0.6+0.2=0.8, and with this sized pen, the machine has calculated that you can only fit four waves in before the pixel is full, so it draws four waves.

From your pen width tests, it looks to me that your actual pen width is between 0.4 and 0.6mm. There are still some slight gaps in the ink on the 0.6mm pixel, but the ink is also a bit bleedy in the paper so it's tricky to tell. Also worth mentioning that many pens (I'm looking at you, Sharpie) increase in tip size over their lifetimes, as they get worn.

Last point: This is defiantly a low resolution output device. To capture lots of spatial data, you need to draw giant, or use tiny pens, or enjoy the artefacts and limitations that come out of the process. Aggressively cropping images is also an interesting path to take.

sn