Photography: Portrait conversion to pop art

The effect that we’re going to learn in this tutorial is based on halftone, so it’s essential to know a couple of things before we start. Offset printing uses halftoning in CMYK (cyan, magenta, yellow and black) colors.

Halftone is a technique where dots (but not necessarily round) are printed in rows at a certain angle (traditionally in printing, the angles are 15° for cyan, 75° for magenta, 0° for yellow, and 45° for black). The rest of the colors are obtained from these four, either by proximity or by absorption when printing dots on top of one another. This might sound complex, so let’s try something. Grab a newspaper and a magnifying glass, and look at any photo printed in that newspaper. See the dots?

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The angles mentioned before are the standard ones used in the industry. However, this is going to be a creative exercise, so you can try using different angles if you wish. The angles have much to do with how people perceive colors, so if you’re interested in this, you can look for more information.

For starters, we need to choose a picture for the halftoning—you know, that cool pop art effect seen in Warhol’s works simulating offset printing. This is the one I’m going to use, but feel free to try your own.


Getting started

Let’s see the requirements that need to be fulfilled in order to begin working on this halftoning properly. Open the picture in Photoshop when you’re ready.

Step 1

You might think that a tutorial is not necessary for this, especially when we can locate this effect in Filter → Pixelate → Color Halftone. Yes, this is the easiest way, but I only recommend it if you’re working on something very simple. In fact, if you want to apply this effect to only one color channel, you won’t have any control over it.


Step 2

If you’ve tried the method I’ve just mentioned, undo it by pressing Ctrl + Z or just close the document without saving and start again.

Now, we need the CMYK color mode. If your picture is using a different mode or you don’t know which one it’s using, go to Image → Mode. If there’s a tick next to CMYK Color, then you’re good to go. Should that not be the case, then just click on CMYK Color. The picture that I’m using for this tutorial has the RGB color mode, so I need to switch modes.


Notice that, after switching modes, some colors look duller now.

Step 3

Go to the Channels panel. If you can’t see it next to the Layers panel, open it by going to Window → Channels.


Step 4

Let’s divide the picture into different channels so that we can work with them individually. Open the Channels panel menu and select Split Channels.


You’ll see a new Photoshop document in grayscale for each of the channels composing the picture. Next, we’re going to work with the halftoning on each of these channels. Ready when you are!

Creating the halftone

Alright, let’s begin with the halftone effect. Remember that in this industry the standard angles used for offset printing are 15° for cyan, 75° for magenta, 0° for yellow, and 45° for black. Let’s get to it!

Step 1

You may begin with any channel. As for me, I’ll begin with the cyan, so select the document whose name ends in “_Cyan” and go to Image → Mode → Bitmap.


Step 2

By default, Photoshop will use the output value from the original picture, which in this case is 300 dpi. It’s best for us if the halftone effect shows big, visible and clear dots. A good way to achieve this is by increasing the output value to double or triple the input value.


Step 3

To finish with panel, change the method to Halftone Screen…


After pressing OK, a new panel will pop up.

Step 4

This is where we’re going to actually set up the halftone effect. Remember, we’re working with cyan, so the angle should be 15°, but you may try other values to see what you get. The frequency value determines the number of lines per inch. We want the dots to be big enough, so choose a low value, between 2 and 9. As for me, I’ll go with 2.


Step 5

As its name suggests, the lowermost option determines what shape the dots will have, for example, diamonds, ellipses, squares, etc. I’ll set it to round, but you can try other shapes and see the different results.


Now we’re done with the cyan channel, so just repeat this process with the remaining channels. Next up is combining the four channels into a single image again. In case you’re interested, I’m going to explain how to choose your own frequency values (if not, then just skip to the next step). I’ll also try to explain why you should choose these values.

The values are not chosen at random. In fact, a wrong choice may ruin how the picture looks. So, first and foremost, you shouldn’t use the same angle for two channels. Not just that—we also need to take into account other considerations. For example, if we assign an angle of 0° to the yellow channel, we mustn’t assign 90° to another.

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I recommend that you assign to the strongest color, which in this case is black, an angle of 45° to neutralize its weight, and then assign an angle of 0° or 90° to yellow, which has the least contrast, to make it more visible. Finally, you should assign angles close to 45° to both cyan and magenta, having in mind that there should be a difference of at least 30° between each one and black. So, for example, if black has been assigned an angle of 45°, then cyan could be at 15° (45°-30°) and magenta at 75° (45°+30°).

Don’t worry too much about it. This is a creative exercise, so it’s important that you try different values and see the results.

Step 6

To combine all channels into a single image again, they need to be in grayscale. So, once again, go to Image → Mode → Grayscale.


Step 7

In this panel, the size ratio determines how the resolution of the image will be rendered. As I previously chose an output value equal to triple the input when converting each channel to bitmap, I should set the size ratio to 3 too here.


Repeat this step with the other channels.

Step 8

Select any split channel document. Then, open the Channels panel menu and choose Merge Channels…


Step 9

You’ll see that the mode is set to Multichannel by default, but that won’t do in our case. We need the CMYK Color mode and just four channels in total.


Step 10

Make sure that Photoshop has chosen the correct split channel documents and then press OK to merge them.


The exercise is pretty much done, but one of the advantages of using this method is the ability to achieve creative results by turning off some channels. For example, here’s what happens if we hide the magenta channel.


You could even try to apply the halftone effect to only some channels, not all of them. For example, here’s what happens if you apply it to all of the channels but magenta (which is not hidden in this case), assigning an angle of 15° to both cyan and yellow, and 75° to black.


Before we wrap things up, I’m going to tell you how else you can make the most of this effect, so hang in there!

Other uses for this effect

If you’re interested in screen printing, here’s a suggestion for you: save the split channels individually and then try to come up with different uses for them. For example, you could prepare sheets for a four-color screen printing. Does T-shirt printing ring a bell now?

On the other hand, if you prefer a monochromatic approach, you could use Photoshop’s Color Halftone filter to have your image in a single color. Whether you go for monochrome or four-color, make sure the dots aren’t too small, otherwise the image won’t look right.


It’s done!

This is it! I hope that you enjoyed this tutorial. If you have any questions, I would be more than glad to answer them. Oh, and don’t forget to share your results! Thank you very much and see you next time! 🙂