Algorithm 1: Histogram modification in L*a*b* space

Input:  $I_{RGB}$—image in RGB space 1 convert $I_{RGB}$ into $I_{L\ast a\ast b\ast }$; 2 divide $I_{L\ast a\ast b\ast }$ into separate channels; 3 leave $a\ast$ and $b\ast$ channels without any changes; 4 transform $L\ast$ channel to the [0 1] range; 5 perform certain histogram operation on $L\ast$ channel; 6 transform back $L\ast$ channel to the [0 100] range; 7 combine $I_{L\ast a\ast b{\ast }^{\prime }}$ from separate channels; 8 convert $I_{L\ast a\ast b{\ast }^{\prime }}$ into $I_{RG{B}^{\prime }}$; 9 return $I_{RG{B}^{\prime }}$—modified image in RGB space;