iPhoto for iOS has several options for turning photos black and white-some are obvious, while others are a little less so.
Easiest way: use the Effects tool
The most straightforward way to get the black and white effect is to use iPhoto’s Effects tool. The Effects icon offers a series of tools that can make great enhancements to your photos. Tap the icon (the last in a series of editiing icons), and then select Black & White from the available reels.
Let’s start with sepia. Hit the cream-colored button to bathe your photo in a sepia tint. If you look at the mini photo-reel at the bottom of the screen, you’ll see six smaller versions of your photo and a blue vertical line. Drag the vertical line from left to right with your finger, and the black, white, and sepia contrast will change.
The middle bubble is for adjusting black and white contrast and grain. Again, move the blue vertical bar from left to right to see the changes. Use this tool to sharpen the photo, emphasize shadows, and increase contrast.
The vignette bubble places a vignette around the image, with heavier shadows in each corner of the photo to draw focus to the subject in the center. Just like the other bubbles, you can slide the blue vertical bar to see the border corners adjust.
Now, exit out of Brushes and tap the color pallet icon right next to it. Check out the rainbow box. This adjusts the overall color of the whole photo. Slide the silver knob all the way to the left, and watch the color fade from your photo and make it a soft black and white.
The Exposure tool (camera aperture icon) can change the look of your black and white image once its been transformed with one of the other tools. Changing the exposure will change the shadow emphasis, definition, and quality of the black and white contrast to give your image some extra pop. Use this tool last to polish the photo to your liking.
Whatever adjustment technique you decide on, experiment with each tool first to find the one best suited to make your photo shine. Each will have its own strengths and weaknesses depending on the original photo.