Histogram of image pixel intensities and the density of a particular intensity

[tim.holy]

If this isn’t a homework question, see

https://juliaimages.org/latest/democards/examples/spatial_transformation/histogram_equalization/#Histogram-equalisation

If it is, you shouldn’t look, because it’s the exact answer and you’ll lose out by not figuring it out on your own. Instead, read the documentation for https://github.com/JuliaImages/ImageContrastAdjustment.jl