With ImageMagick 7, you can do Otsu thresholding.
Input:
magick check.png -alpha off -auto-threshold otsu x.png
Result:
There is no built-in equivalent in ImageMagick 6. However I have a script, otsuthresh that will do that At my web site
So in ImageMagick 6, you just have to do simple thresholding.
convert check.png -alpha off -threshold 50% y.png
Result:
I note that your input image has an opaque alpha channel which needs to be removed to get proper results.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…