I'd like to be able to crop SVG chemical structures, completely (see this question), that were created using MarvinSketch and I think I might have thought of a solution; I use MarvinSketch to create a large PNG file, then crop that using GIMP, and then convert the PNG to SVG. Hence I'd like to know if anybody knows a free software I can install (I don't like using online converters as I'm always suspicious of malware) on Ubuntu for high quality PNG->SVG conversion.
So you are looking for raster to vector graphics converter/tracer.
autotrace both are in Ubuntu repository. Myself I tried
potrace before which gave nice results with default options. As I remember, both tools do not support compressed formats as input, only bitmap images.
See Potrace examples
Potrace: utility to transform bitmaps into vector graphics
potrace is a utility for tracing a bitmap, which means, transforming a bitmap into a smooth, scalable image. The input is a bitmap (PBM, PGM, PPM, or BMP format), and the default output is an encapsulated PostScript file (EPS). A typical use is to create EPS files from scanned data, such as company or university logos, handwritten notes, etc. The resulting image is not "jaggy" like a bitmap, but smooth. It can then be rendered at any resolution.
potrace -s inputfile
AutoTrace: bitmap to vector graphics converter
AutoTrace is a program for converting bitmaps to vector graphics. The aim of the AutoTrace project is the development of a freely-available application similar to CorelTrace or Adobe Streamline. In some aspects it is already better. Originally created as a plugin for the GIMP, AutoTrace is now a standalone program.
autotrace -output-format svg inputfile
There are more GUI that added tracing feature, like Gimp & Inkscape. See Hussein El Motayam's answer.
Here also Wikipedia: Comparison of raster-to-vector conversion software, not every tool. To anyone interested in comparing results, I would like to ask reporting results to free open source tools so they can ameliorate.
Inkscape has got an awesome auto-tracing tool.
- Install Inkscape using
sudo apt-get install inkscape
- Import your image
- Select your image
- From the menu bar, select Path > Trace Bitmap Item
- Adjust the tracing parameters as needed
Check their tracing tutorial for more information.
Once you are comfortable with the tracing options. You can automate it by using CLI of Inkscape.
convert command in the terminal :
convert EXAMPLE.png EXAMPLE.svg
Here's some info from the manpage:
convert(1) - Linux man page Name convert - convert between image formats as well as resize an image, blur, crop, despeckle, dither, draw on, flip, join, re-sample, and much more. Synopsis convert [input-options] input-file [output-options] output-file
I just have used gimp right now with amazing results. I first used potrace but all I got was an image all in black with a lot of distortion. Maybe I didn't used it properly but when I tried with gimp just exporting as "eps" (file_name.eps), it was all done. All I have to do was review it setting the resolution with a value of 300. That's it.