It looks like you are allocating a rather small image:
If you need bitmap images, would it be possible to allocate a larger image, and draw the strokes larger too? For instance:
ofScale(3, 3, 3);
before drawing the stroke to make it 3 times larger.
If you don’t need bitmap images you can indeed export vector files like SVG, PDF, DXF or something else. It depends on what you want to do with the output.