Improve strokes of the exported image

[nachouve]

When using draw_signature(), the signature is composed by rect-lines. So, it is a bit different and you can notice angles in the signature exported.

Here an example:

Checking the jSignature demo I see that they do not have this problem when exporting to other formats.

[SebCorbin]

Could you try adding joint='curve' to the ImageDraw.line() call (docs) and tell me if that fits your needs?

[nachouve]

I'm afraid that doesn't solve the problem.
It just rounded edges at the end of the lines.

It's prettier, because it fills small gaps in... but you can see that the strokes are still straight lines.

Could it be a matter of increasing the number of points collected in the canvas? Is it possible?

[SebCorbin]

We're already using "native" vector export https://github.com/brinley/jSignature#data-import--export-and-plugins which does not compress data (and is the format used by jSignature strokes to store while signing).

I think the issue is in trying to recreate the shape with PIL, I'll be adding the joint='curve' option anyway as it's a better render.

[nachouve]

Thank you!

I did some testing on the jSignature demo and I think the "svg" formats perform better in this particular matter. I don't know if it can help in any way.

[SebCorbin]

So now it depends on your use case:

• either you need the exported image on the server side, and you're stuck with PIL, or you could try to render the svg with CairoSvg
• if you want to export the image on the browser side, you can fire up jSignature and load the data, then use the "image" export format to get a PNG

[nachouve]

I found that jSignature do this "magic" to smooth the strokes in the screen:

http://willowsystems.github.io/jSignature/%2523%252Fabout%252Flinesmoothing%252F.html

So maybe we are loosing all that stuff with the process of iterating points for creating lines. It does not look simple...

[nachouve]

Just another idea...

Use ImageDraw.arc instead of ImageDraw.line, but start angle and end angle have to be calculated for each.