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I'm looking for an app for tablet that will let me draw lines with a stylus that I can later continue to edit in illustrator. All apps that I have seen until now will convert every stroke into an area - expanding the stroke. I would like to keep the stroke as a single line, with editable anchor points.

For my job I often have to make black + white line drawings of organic shapes in illustrator. My process until now is hand-sketching with pen + paper, then scanning to illustrator and re-drawing everything with pen tool. There has to be a quicker way.

Thanks and best

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  • ermm.. there is Adobe Illustrator for tablets. I, personally, can't comfortably draw on any tablet using any app. The nature of "hover your wrist" doesn't work for me.. and who wants to constantly be looking for a smudge glove :);
    – Scott
    Sep 8, 2023 at 9:45
  • The Illustrator app is for iPad only. For Android there's an app called VectorInk - but it requires a monthly subscription plan if you want to save your work, however the free version lets you export SVGs. Might be better to just get a wacom tablet and use as an input device for Illustrator.
    – Billy Kerr
    Sep 8, 2023 at 10:13

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Illustrator Inkscape and Corel have all single stroke tracing modes. The name can be centerline or something. Their problem is the inability to understand crossings and pencil lines which are blurry or have a widely varying intensity. Some stand-alone tracing applications which are designed for tracing maps and technical drawings are a little better in crossings, but fail with pencil lines.

Intensity variations can be partially compensated in GIMP or Photoshop or other image editor (apply curves), but that's generally not enough if the lines are made by a fast working pencil sketcher.

If you have plenty of line crossings or large line intensity variations your best option is still to redraw as a vector on the scanned image.

If the number of the line crossings is reasonably low you can wipe clean zones around one of the lines at every crossing. A corner may need the same treatment to avoid rounding. Then the centerline tracing works. You can later insert a line segment to patch the wiped section easily. Probably moving the end anchor point + joining does the trick.

The next image has a scanned bitmap image in the left. It's not perfect because the resolution is not especially high. But there's no pencil intensity variation problems. A typical centerline tracing result is in the right. Crossings are wonky and corners are rounded:

enter image description here

The example is in Inkscape. Here's a zoomed view of the problems:

enter image description here

If one paints a little white to the bitmap image to those places which are marked with green in the next image, he gets a better tracing result:

enter image description here

Now there's no problematic crossings nor corners. The tracing result is this:

enter image description here

After selecting the end nodes of the gaps, inserting a line segment and removing the extra nodes the result is this:

enter image description here I'd say it's much better. But it needs manual work. The work is surely less than drawing manually everything. Hopefully the programmer who wants to implement this as an automatic or semi-automatic add-on to generally available tracing programs is already born or at least begins soon to sprout somewhere.

There are online services (free and paid) which trace images and give the result as vector (PDF, SVG, DXF). Some of them make centerline tracings, too. Just one example:

https://online.rapidresizer.com/tracer.php

I haven't still seen one which makes even close to perfect centerline tracings. The results are at best as bad as in Inkscape or Illustrator. Many online tracing sites do not even know the "centerline tracing".

One thing: My answer ignores recent artificial intelligence developments. It's well possible that there exists some experimental applications which are much more capable in guessing the wanted lines than our ordinary graphic programs. Of course, extracting automatically military intelligence data (for ex. the roads without getting confused in crossings) from satellite and aerial photos has needed a solution for the same problem a long time. But I'm afraid the owners of such software technology stay silent.

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