Posted by dellus on Dec 03, 2016; 10:41pm
URL: https://forum.librecad.org/Difficulty-changing-line-width-tp5714453p5714464.html

I cannot reproduce this, it works for me.
linetest.dxf





As it is difficult to impossible to completely control the result of "export as image" I recommend to make a pdf of the plan first. So go into print preview and make your setting as if you would want to print to paper (don't forget to set the proper paper size in "current drawing preferences"). Stay in print preview and "export as pdf".

linetest.pdf

In an other software like inkscape or pdf-xchange viewer (very nice) you can then convert the whole sheet to an image of desired resolution, about 300 dpi and png as format recommended.

linetestpdfxc.png 

In an image editing app like Irfanview or xnview you can cut out any part of the whole if needed.
The quick-shot way is not always the best.
Do not choose line thickness with visibility in the jpg in mind, but use standards as used for paper drawings. That's roughly 0.25 mm for normal object lines, 0.5 mm for the outline of cut parts and maybe 0.13 mm or 0.18 mm for auxiliary lines, 0.35 mm may be used for dashed axis lines.