Printing Grayscale Image has horizontal lines

Hi, 

I'd like some advice on how to print grayscale images on the canon mf267dw laser printer. 

If I print a color image straight to the printer, it appears not too bad.

But when I print from ANY other program, for example Gimp and grayscale the image first it appears with horizontal lines through it. The horizontal lines are not missing ink - so no need to maintain the printer (it doesnt do this when I print straight from a color image).

So is there an ysetting I can change to experiment with printing from grayscale images to fix horizontal lines ? 

Thanks for reading.