cannot vectorize image with gradient background

[jnweiger]

This leaf gives me a headache. All I can do currently is this:

Original image from #15 by @trader4300:

[Moini]

It works with the rectangle option. Maybe it has to do with the background and the stroke color being uneven?

[jnweiger]

That is so cool! I added the cliprect for something completely different. And you solve a new problem with that. Love it! That is the workaround for that issue. :-)

It is definitly being fooled by the coloring of the background.

[Moini]

I don't know about the type of preprocessing you're doing - would being able to define a threshold for black/white help with this? Or maybe it could determine that from the image itself? The cream and white are quite different from the grey/black.... Just thinking out loud - I don't know at all how to do this, or if it would help.

[Moini]

(and yes, it is cool :))

[jnweiger]

Try this: python-2.7 with Pillow-5.1.0 or python-3.6 with Pillow-5.2.0

from PIL import Image, ImageOps
im = Image.open('leaf-issue15.jpg')
im = im.convert(mode='L', dither=None)
ImageOps.autocontrast(im, cutoff=2).show()

Wow, that looks like Pillow is misbehaving! No wonder poor autotrace has trouble thereafter!

[jnweiger]

• Opened Autocontrast cutoff behaves unexpectedly python-pillow/Pillow#3331
• Removing the cutoff in version 0.8c

[Moini]

Urghs! So the cutoff is actually the culprit... :/ How weird. Do you mean to add the functionality back in when the linked issue is solved (or check for version numbers?)

[jnweiger]

hmm, probably not worth it. cutoff=2 was more a safety idea than a necessity.

[Moini]

Okay, thanks!