Whys is my iPhone 4 display showing darker areas and scanlines?

I opened my iphone to change a broken dock connector and the volume switches now they work but I have a new problem.

I'll do my best to expain... There seems to be an inconsistency in the intensity of the brightness. It seems like the dark areas are being brighter than they should.

However, whenever there is something very bright, like white or close, in the horizontal bands that contain the white areas, the intensity of the black areas enclosed look correct.

Do you think I need to replace the lcd assembly or could it be easier?

I know, it's tricky to explain so here are some pics. Unfortunately I couldn't get to photograph the scanlines.

Thanks in advance!