Why is my plot pale?

I have a problem with the following ParametricPlot:

ParametricPlot[  ReIm[(1 + I) (x + I y)],  {x, -1, 1}, {y, -1, 1},  Mesh -> None,  PlotPoints -> {50, 50},  MaxRecursion -> 3,  Axes -> None,  PlotStyle -> {Texture[img4], Opacity[1]},  BoundaryStyle -> None,  Frame -> None   ] 

(This code should simply turn the chessboard-like tiling by Pi/4 and scale it.) The original texture looks as one would expect (saturated black, white). Why does the output image look so pale (despite the Opacity[1] command)?

I am probably missing something obvious but lots of trying different approaches did not solve the problem. Thanks for your help!

enter image description here