====== Sharpness ======

We define sharpness as the difference of brightness (the pixel's \(L\) component in HSL color space) from a pixel to its neighboring pixels.

Sharpness for each pixel is calculated based on the values of immediately surrounding it pixels, only the luma component \(L\) is used for this calculation.

A pixel's new value is calculated based on the simple matrix (see below) with a little twist: the central coefficient of 5 is adjusted based on the new value of sharpness as follows: \(coef_5 = 5 + sharpness\), where \(sharpness\) is in range \([-1..+1]\).

\[ 
\left[ {\begin{array}{ccc}
 0 & -1 & 0 \\
 -1 & coef_5 & -1 \\
 0 & -1 & 0 \\
\end{array} } \right]
 \]