Working with paths exported from Gimp

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lndyosh
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Working with paths exported from Gimp

Postby lndyosh » Tue Dec 25, 2012 1:16 pm

Hi,

I'm doing some work involving bitmap tracing and having a bit of trouble with the overwhelming amount of nodes that Inkscape draws from the original file. I tried setting Optimize paths and Suppress speckles to acceptable maximums (the compromise here is between the sharpness of the outline and the amount of "extra" pixels), but it's still impractical.

What I tried to do was to run my image through Multiple Scan: Colours in Inkscape to reduce it to a smaller set of colours (3-4) (I found that posterize in Gimp created to much distortion), then export the image to Gimp, create paths from Fuzzy Select (selection by colour) and then export these paths to SVG. All was going swimmingly until I opened the paths in Inkscape. You see, in Gimp they were perfectly aligned with each other, like pieces of a puzzle, together forming the outline of my image with each path representing a colour shade. When I opened the exported SVGs in Inkscape, however, this alignment was broken. Does anyone know how Inkscape decides where to put imported paths? I changed the Inkscape document size to match the size of the paths' canvas, but to no avail. Paths still end up all over the place.

I've attached the file I'm trying to trace. The ripples on the water are creating a lot of junk pixels which is why I thought my Gimp workaround would be ideal. Any ideas how to solve this (other than to get a better shot of flying pigeons)?
Attachments
Pigeons tracing.png
Pigeons tracing.png (165.15 KiB) Viewed 1434 times

lndyosh
Posts: 11
Joined: Mon Dec 24, 2012 10:25 am
Location: london

Re: Working with paths exported from Gimp

Postby lndyosh » Wed Dec 26, 2012 11:13 am

Right, figured it out myself: When exporting paths in Gimp, have to make sure that you select "Export All Paths from This Image" in the drop-down menu. The default option is to export paths individually, which screws up their relative positioning.

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brynn
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Re: Working with paths exported from Gimp

Postby brynn » Wed Dec 26, 2012 11:32 am

Is it just the pigeons that you want? You could try SIOX Forground Selection technique (see manual for instructions). It might not work, because the ripply water could confuse the trace engine. But easy to try!

lndyosh
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Location: london

Re: Working with paths exported from Gimp

Postby lndyosh » Fri Dec 28, 2012 5:15 am

Yes, their outlines and colour profiles. I want to transform them into a two-colour (black and white) stencil. I really liked the results of running multiple colour scans in Inkscape - they seem to doing more than just reducing the image to 2,3,4 colours as Posterize does. Do you know how their algorithms are different from each other?

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brynn
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Re: Working with paths exported from Gimp

Postby brynn » Fri Dec 28, 2012 8:53 am

You mean how are the algorithms of Inkscape's Trace Bitmap are different from GIMP's Posterize? Apart from one is vector and the other is raster, I have no idea! Not only am I not sure what an algorithm is (beyond being some sort of mathematical calculation) I've never even used Posterize. Maybe someone else can answer that? Or you might find some answers at at the Inkscape wiki (http://wiki.inkscape.org/wiki/index.php/Inkscape).

[Hhhmmm.....somewhat random thought, perhaps a result of the slight fever I'm running.... Trace Bitmap is based on a program called PoTrace, which by itself only makes black and white images. Maybe "Po" is short for "posterize"?? So maybe they are actually quite similar????]

Anyway I'm glad you're getting something you like with Inkscape :D

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RobA
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Re: Working with paths exported from Gimp

Postby RobA » Fri Jan 04, 2013 6:45 am

lndyosh wrote:Yes, their outlines and colour profiles. I want to transform them into a two-colour (black and white) stencil. I really liked the results of running multiple colour scans in Inkscape - they seem to doing more than just reducing the image to 2,3,4 colours as Posterize does. Do you know how their algorithms are different from each other?


The gimp posterize is just nasty as it works in some funky colourspace, posterizing across R/G/B individually, not what is expected by users.

I wrote a posterize replacement gimp script to do a better job: http://www.silent9.com/incoming/scripts ... ndexed.scm

Saul Goode also wrote a similar one with a smoothing option: http://chiselapp.com/user/saulgoode/rep ... g-quantize

-Rob A>
Last edited by RobA on Tue Apr 23, 2013 12:02 pm, edited 1 time in total.

v1nce
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Re: Working with paths exported from Gimp

Postby v1nce » Fri Jan 04, 2013 7:11 am

RobA wrote:The gimp posterize is just nasty as it works in some funky colourspace, posterizing across R/G/B individually, not what is expected by users.


What did you want to spot ? That posterize is not the good tool for color reduction ?

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RobA
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Re: Working with paths exported from Gimp

Postby RobA » Mon Jan 07, 2013 10:30 am

v1nce wrote:
RobA wrote:The gimp posterize is just nasty as it works in some funky colourspace, posterizing across R/G/B individually, not what is expected by users.


What did you want to spot ? That posterize is not the good tool for color reduction ?


It very much depends on the image, but I would personally never use the built in gimp posterize to colour reduce an image. The two I linked two are much closer to the photoshop posterize version. I am not sure how either compares with the inkscape scan bitmap multiple scan option.

-Rob A>


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