Project image onto curve

[Akir]

Hey all,
I'm looking for a way to project a picture onto a cylinder like here: http://gimpforums.com/thread-project-ima...tary-curve
- progressively shorten one axis while leaving the other axis unchanged. I get the idea of the displacement map, but I can't get the gradient right - I don't really get ofnut's formula, nor how to implement it into a gradient...
Thanks in advance,
Akir

[Ofnuts]

Filter>Map>Map object>Cylinder (yes, I learned new tricks since 2010 )

For the same price you get lighting effect (shadows etc...)

[Akir]

Nope, that's not it, with that filter both axes get warped ("front" is spread, while "back" gets contracted). I need to restrict the filter to just one axis - it's not art, it's more a technical drawing.

[Ofnuts]

(10-23-2017, 05:24 PM)Akir Wrote: Nope, that's not it, with that filter both axes get warped ("front" is spread, while "back" gets contracted). I need to restrict the filter to just one axis - it's not art, it's more a technical drawing.

Uh? Can you show a screenshot?

[Akir]

Here's before and after Map to Object/Cylinder, and the third one is what I'd like to get. I admit I asked the same question years ago in some gimp forum out there, but I can't find it anymore. I did get an answer back then, so I know it's possible if the displace map is configured correctly, but I have no memory of how that worked...

[Ofnuts]

The trouble with displace is that it blurs things horribly. A completely different method:

• Create two paths, that are single vertical lines (the two lines on the sides)
  
• Use my path-inbetweener script to generate the lines in between (the "Swing" strech is exactly a sine function ,so is exactly the projection of the side of  a circle on a line).
  
• Merge the paths (you just need to do "merge visible paths" in the paths list)
  
• Perhaps add the horizontal segments manually
  
• Edit>Stroke path
  

   

[Akir]

Thanks, nice tool! (I'm also using your delete-strokes tool a lot, btw., it saves me hours of work regularly, thanks for that as well!)
In this case it's not what I need though - the pic I used is just an example, the actual pictures I want to wrap are more complex drawings, won't work with paths.
To be precise, my plan is to copy the decoration of Roman Samian ware bowls (like this one for example: https://en.wikipedia.org/wiki/Terra_sigi...r_29_2.JPG ) onto paper, and after scanning, correcting, cleaning up, and so on, put the result into a digital drawing of the pot outline, to achieve something like this: http://potsherd.net/atlas/types/sigillata/form/DR37 .
I know the blurring is an issue, I haven't found a way around that yet. It's less visible though in my projects, since I work in at least 1200dpi usually.

[Ofnuts]

You should really look into using Blender for this.

PS: Btw: delete-strokes has been enhanced and repackaged with a few other scripts as ofn-path-edits.