Technically, the Posterize adjustment in Photoshop is designed to analyze the pixel colors of a selected area of an image and reduce the number of colors—while maintaining the “look” of the original image. Creatively, you can apply this adjustment to make photos look like wood-block color artwork.
3. When selecting Posterize, you’ll see this simple dialog box. You can change the effect by typing a different number in the Levels window. Here, I’ve selected 4. The more you increase that number, the less the image looks posterized. At first, you may be thrilled with the default setting, but I encourage you to play around with the different settings. You might be pleasantly surprised at what you’ll come up with. Also, even after you’ve chosen a setting, experiment with Curves, Levels and so on to see how you can further enhance a picture.
5. Now try this: Convert a photograph you want to posterize to a black-and-white image first. Changing the color mode to grayscale (Image > Mode > Grayscale) is an easy way to go, but it’s not the best way to get black-and-white from color. If you do use the grayscale conversion, try boosting the Contrast (Image > Adjustment > Brightness/Contrast) a bit for a more dramatic image. For more control, however, use Channel Mixer (Image > Adjustment > Channel Mixer) and check the Monochrome box. With Channel Mixer, you have—that’s right—control over the tones in the different channels.