How would I add a scale bar to images?

[afvrbanac]

Hello, novice user here with some basic questions. I'm using histolab to extract random tiles at different levels. Is it possible to automatically add a scale bar to these images?

Also, is the magnification of each level the original magnification divided by the downsample for the level? So for example, for a 40X image at level 0, if the downsample for level 2 was 16, the magnification would be 2.5X?

[ernestoarbitrio]

Hi @afvrbanac I will transfer this issue in a github discussion!!! 😄

[nicolebussola]

Hi Alison, thank you for your questions, absolutely not trivial. Regarding the possibility to add a scale bar, we haven't thought of that as it is not optimal to have that if you want to use the tiles in a machine learning/deep learning pipeline. We can try and add the scalar bar as an optional parameter when saving the tiles (do you have specific needs?).

Regarding the magnification level, your guess is correct; I have checked with an expert pathologist on a few samples and the conversion holds, so you can do the math by reading the downsample factor for each level by using the .properties method of the slide. I think that this conversion might be a nice feature to have so we will definitely add this on our next release, so thank you 😄
Best
Nicole

[afvrbanac]

Thanks Nicole, this is very helpful! Yeah I'll be using the tiles both for machine learning purposes and they will also be manually annotated in ImageJ for comparison (the annotator had requested a scale bar which is why I was asking).