If you print vertical lines (i.e. in the direction of an "I") it can appear quite light for smaller pixel counts.
The problem is that vertical lines require the thermal head to ramp up/down quickly.
Horizontal (i.e. underlines, borders) are easy, just turn the heat on and let it burn.
My solution (which I use in any case) is to generate my 224 x 96 px image, then "smear" it to 225 x 96 px.
That is, logical or the image with the image shifted horizontally (user viewpoint) 1 pixel.
I think that you will find that the line densities track better.
Of course, you could just draw all vertical lines one pixel wider than horizontal lines.
But since this is systemic I prefer to fix it with post processing.
If you print vertical lines (i.e. in the direction of an "I") it can appear quite light for smaller pixel counts.
The problem is that vertical lines require the thermal head to ramp up/down quickly.
Horizontal (i.e. underlines, borders) are easy, just turn the heat on and let it burn.
My solution (which I use in any case) is to generate my 224 x 96 px image, then "smear" it to 225 x 96 px.
That is, logical or the image with the image shifted horizontally (user viewpoint) 1 pixel.
I think that you will find that the line densities track better.
Of course, you could just draw all vertical lines one pixel wider than horizontal lines.
But since this is systemic I prefer to fix it with post processing.