isp:sharpness

# 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 $[-1..+1]$.

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