Non Linear Remapping of the Pixel Values
Yes, using a non-linear mapping function on the intensity. Let us for the moment suppose you have a grayscale image (because of the words "black and white", "shadings"), with luminance $0\leq p_{i,j} &lt;1$. 

The piecewise linear mapping: $f( p_{i,j}) = \frac{p_{i,j}}{2}$ if $p_{i,j}&lt;\frac{1}{2}$, and  $f( p_{i,j}) = \frac{3}{2} (p_{i,j}-\frac{1}{2})+\frac{1}{4}$ if $p_{i,j}\geq\frac{1}{2}$ can do the job. 

This is a simple example of "Non-linear Contrast Enhancement". If that works for you, you can try with smoother functions.