Scale bar does not correspond to the actual size

Dear all, first of all, thank you very much for this, scalebars are kinda mandatory in research and having this in python is really nice. I am having some issues when using ScaleBar. The bar does not correspond to the actual size it would have; could you help me with that? I’m using this code:

from matplotlib_scalebar.scalebar import ScaleBar
from skimage.io import imread

len_px = 0.00048223304582578836

image = imread('dur_grain1apatite01.tif', as_grey=True)

fig, ax = plt.subplots(figsize=(15, 10))
ax.imshow(testimg_apatite)
scalebar = ScaleBar(dx=len_px,
                    units='mm',
                    fixed_value=25,
                    fixed_units='um',
                    location=4,
                    box_alpha=0,
                    font_properties={'family' : 'monospace',
                                     'weight' : 'semibold',
                                     'size' : 20})
fig.gca().add_artist(scalebar)
plt.show()

This is the example image. Thank you very much for your support.

[ppinard]

I will close this issue not to cause confusion. Please reopen if you think the problem is still there.

[ppinard]

Thank you both for your comment. You are 100% right there was a mistake in the code. After many attempts to understand the problem I realized that the “bar” of the scale bar was drawn with an edge around it 😞 This made the “bar” appeared longer. Making the bar longer (with the length_fraction) helped because the error due to the edge decreases as the length of the bar increases.

I tried @parishcm’s example and I got a length of 10.0769 in ImageJ. I committed a fix and I will release a new version soon.