Making my images black and white

Because I hand drew my illustrations they weren't pure black and white when I scanned them in. Therefore, I had to change the levels of each one. I started off using the white paint bucket to fill in each image, but fortunately realised a few of images in, that this was a very unnecessarily long way to do so. In a couple of the images it is still very slightly noticeable that areas are off-white, but in amongst the many flip book pages they hopefully go unnoticed.