This works and is more Mathematica style code.
SetDirectory[NotebookDirectory[]];
img = Import["55th-All-Japan-Kendo-Champ2007-4.jpg"];
colorXform[p_] := p[[1]]*0.3 + p[[2]]*0.5 + p[[3]]*0.2;
newImg = Image[Map[colorXform, ImageData[img], {2}]];
Show[newImg]