If you look really closely at an image in a printed newspaper or magazine you’ll see that what appears at first to be “continuous tone” (like a photograph) is actually constructed of thousands of tiny spots. This is called a halftone. But if you make those spots bigger, you break the illusion and the spots (or dots or whatever you want to call them) become an integral part of the image itself.
But how can you make these halftone effects yourself? It turns out to be super easy in Photoshop.
To make the four-color “rosette” halftone in the middle of the image above, I simply chose Filter > Pixelate > Color Halftone. On a color image, you get multiple halftones that overlap. But on a grayscale image, you get circular dots that grow larger and larger:
Making Better Halftones
The Color Halftone filter does an okay job of making halftones, but there is another, far more powerful method. This is what I usually do:
First, here’s the image that I’m going to be working with:
I just made it by creating an “angle gradient” in Photoshop and then running the Twirl filter on it. I want a black-and-white halftone, so I’ll first convert the RGB image to Grayscale:
And then I’ll head back to the Image > Mode submenu and choose Bitmap. When I do this, Photoshop asks me what I want to do with gray tones in the image:
If I choose Threshold from the Method pop-up menu, then Photoshop simply makes all my dark gray pixels black and light gray pixels white. That’s not very interesting. Instead, I choose Halftone Screen from the Use pop-up menu and click OK. This is where the real control lies:
You can choose a Frequency, an Angle, and a Shape for the halftone. In the image at the beginning of this article, I used the Round shape, which makes circles.
But if you look really closely, these are different than the circles that the filter uses. Instead of circles that just get bigger and bigger, they’re circles that actually invert in the darker tones:
This is a more traditional halftone spot shape, reflecting how halftones really look in print.
But you don’t have to use the Round spot here. You can use Line:
…or several other screens. Notice that I’m adjusting the frequency (lower frequency numbers make larger “spots”) and angle of the grid in each of these examples.
Adjusting Image Resolution
I skipped over one important setting earlier on: the Output field in the Bitmap dialog box. This lets you control the resolution of the image after you apply the halftone effect. If you are planning on printing your image, you’re probably going to want to set this to 1000 or more (for super smooth edges on your halftones, I would recommend 1500 or 2000 ppi).
If you’re just making Web graphics, then you’ll want to set this to something smaller. While you may be tempted to use 72 or 96 ppi here for Web graphics, I would, instead, recommend that you use perhaps 300 or so. Then after you make the halftone, use the Image > Mode menu to set it back to Grayscale, then change it back to RGB, and then change the resolution of the image to 72 or 96 ppi using Image > Image Size (by resampling it). This will result in a softer, more elegant effect. Again, that’s just for on-screen images. This also lets you export as PNG or JPEG.
How to Save your Image for Print
If you are printing your high-resolution bitmapped image, you’ll leave it set to Bitmap mode in Photoshop (that just means every pixel is either black or white). Then you can save it as a PSD or TIFF file.
The nice thing about bitmapped images like this is that you can place them in InDesign and then colorize them. (First select the image inside the frame, and then choose a color from the Swatches or Color panel.)
The halftone effect lets you create a vast number of variations from your images. Experiment! Play! Make multiple versions and overprint one over the other.