I have googled extensively on this, and am running around in circles.

I have a program that outputs isobars - lines of equal pressure. I can output these as .ps, .png, .jpg, and .kmz files.

What I need (ideally!) is to get them into omnigraffle, as vectors. This can be achieved if I can get them into pdf format - omnigraffle will happily read that.

I have spent some money on various apps, and have Inkscape, but I am struggling. - If I use a 'convert to paths' tool, it invariable creates shapes rather than lines, to account for what it perceives as different thicknesses. I just want lines. - If I try and 'trace' using the freehand tool on the omnigraffle app, it produces raster lines - not what I want - If I try and 'trace' using the bezier tool on the omnigraffle app or program, it produces something nothing like the image I'm tracing, and is impossible to tweak (I have multiple images)

I've attached an example of the image I'm trying to recreate. I have Inkscape, Omnigraffle, and various apps. Not averse to spending a few pounds on different software, but ideally do not want to shell out for a full copy of illustrator!

Any pointers gratefully received. example image of isobars

  • 1
    It's really too bad you don't have access to Illustrator. This can be achieved very easily in it. If this isn't a long term project, you might be able to get away with the free trial version? Commented Jan 20, 2017 at 16:55
  • 2
    See graphicdesign.stackexchange.com/questions/60107/… for vectorizing to lines rather than shapes.
    – Takkat
    Commented Jan 20, 2017 at 19:14
  • 2
    Oh. My god. Why everyone starts only recomending Ilustrator? James, What program are you using to generate the file? Because there is a chance the .KMZ file format or .PS file are vector information. Actually .PS could be the granddaddy of PDF.
    – Rafael
    Commented Jan 20, 2017 at 20:37
  • 2
    I would merely redraw it by hand, using the image as a manual tracing guide. Better, cleaner, paths that way.
    – Scott
    Commented Apr 22, 2017 at 17:31
  • 3
    Possible duplicate of Convert a line drawing from raster to vector **LINES**
    – Sphinxxx
    Commented May 15, 2018 at 21:44

3 Answers 3


Hopefully this will help you out! These are the steps I took to create a line only (no fills) version of your graphic.

  1. Open your png or jpg file in Illustrator. (Alternatively you can create a new document and drag or place the png/jpg in)

  2. With the graphic selected, choose Image Trace > Make from the Object menu.

enter image description here

  1. Open the the Image trace Panel (Window > Image Trace).

  2. Choose Line Art from the Presets drop down.

enter image description here

  1. Adjust the Threshold to something pretty high (I used 249.

  2. Twirl down the advanced options and make sure that the Stokes toggle is picked and the fills is not.

enter image description here

  1. You may want to play with the Advanced sliders a bit too, to get yourself a better result. This is always a play around and see what happens part for me.

  2. Click the Ignore White Toggle

  3. Once you are happy with what you are seeing on screen, choose Object > Image Trace > Expand

  4. You should have a nice line art image to use. You may need to tweak some of the previous settings if you want things like the type to come out clearly.


I agree that Illustrator is completely overkill for tracing images into vectors. Use Inkscape and use the Trace Bitmap tool.

Select the image in Inkscape. Then use Path menu and select Trace Bitmap.

Click on the OK button to try the default settings.

It creates a vector object (a path) on top of the original, so you have to deselect everything, then click the black part of one of the lines (because it will be the vectored path set) and drag it off to the side. Then you can delete the original if you want. But you might feel safer keeping things on separate layers.

Keep all your work in .SVG for future edits, and export it in whatever format you need to open in Omni-whatsit.

  • 2
    It turns out inkscape's Trace Bitmap tool creates paths using fill, not a stroke like the OP requested. If it can use stroke-only I have not found the option to do that.
    – Mutant Bob
    Commented Oct 21, 2017 at 18:15
  • beg, steal or borrow a copy of Adobe Illustrator (sorry for an ancient version but it still works and does not want regular payments)
  • work some basic tutorials or get a friend to help
  • paste or "Place" your bitmap image onto empty work in Illustrator
  • select the bitmap
  • choose Object > Live Trace > Tracing options
  • put the preview on and try to find proper combination (see the screenshot). The settings are essential for different kind of images to get the wanted features well traced
  • press Trace
  • select and kill the unwanted parts (you should preclean the bitmap image in a photo editor to keep the tracing results manageable)
  • insert the texts and other needed new data
  • save your work


Another option is to use online services. Here is a preview of VectorMagic's output. Probably very good result as a scalable version of your photo. Unfortunately the bad quality texts and the scale were not wiped off before sending it to Vector Magic. These should be inserted afterwards by hand in Illustrator or any Vector Graphics program. NOTE: Commercial services -as usually - want some money.


A third option: Try a dedicated program that is intended for those who scan technical drawings and want to have a DXF (=standard format in technical documents) . Running the trial reveals the usefulness. Do a web search "convert image to dxf" to find them. WinTopo is one example.It has free and paid versions. WinTopo

  • @James Davies new options added
    – user82991
    Commented Jan 22, 2017 at 15:06

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