But i could solve it. I took the negative pictures from this Tutorial: http://note.sonots.com/SciSoftware/haartraining.html They are all grey so i never thought this could be the problem. When i was desperate enough i simply did nearly all i did to my positives to my negatives ( all aside from reducing resolution) Converted all the allready gray negatives into grayscale solved the problem. (in folder : for i in *.jpg; do convert $i -colorspace gray$i; done)