I worked many years using a copy camera to produce 12×18-inch litho negatives. I especially liked the way that high-contrast medium transformed gradual tones into hard-edged images. I like woodcuts and linoleum cuts for the same reason, especially the work of Cynthia Back, one of my former colleagues at the Washington Printmakers Gallery. Click here to see some prints from her 2019 exhibit, RELIEF.
Photoshop has a posterization filter that allows the user to quickly posterize a gray-scale image to a hard-edged image with only blacks and whites. It also allows the user to choose to give the image 3, 4, or more tones. It does not work so well with color images. Without getting into details, what I am looking for is a color image with just a few colors and hard edges — no gradations of tone. I want solids only!
An elegant method of posterization
I am pleased enough with my method of posterization to share it with you. It involves two images. One image I use to generate layer masks. The other is the final image, which has different colored layers, each with a different layer mask. Below is my original image and, below it, my posterized image. This is my second try using this method. Click either image to see it larger in a new tab. The image is sycamore roots growing over a wastewater pipe. It is highly detailed because I used a fixed 50mm lens on a high-resolution DSLR.
Below is a screenshot of the layers palette. As you see, each layer is a solid color. What you cannot see is that each layer only prints if it is darker than the layers below it. In this way the image is built up, with solid white on the bottom layer and progressively darker colors above, each layer with a mask that blocks out more and more of each color until we get to the top black layer with a mask that allows very little of that color to print. The top-most Hue/Saturation adjustment layer allows me to tweak the colors overall. If I want to change the color of any layer, that is easily done.
And here is a screenshot of the image I use to generate layer masks.
Actually, the above high-contrast black and white image looks pretty nice by itself. The bottom layer of the layers palette is a gray-scale version of the original image. At the top is Photoshop’s Posterization filter, set to “2” so that the resulting image is black and white without grays. The middle adjustment layer is a Curves filter. With it, I can adjust the image to make the mask range from light to dark.
Details of the final image
Here are two screenshots of details of the final image. Click on them to see them larger in a new tab. Note how each area of color is solid with hard edges.