Add a quick and easy poster effect to your images using Photoshop to recreate the classic look of posters printed with limited ink colors.
This tutorial will show you how to create a poster effect for images in Photoshop. The term posterize means to limit or reduce the number of colors in an image to recreate the look of a poster printed with a limited number of ink colors.
So instead of a continuous tone image with smooth color transitions, posterize creates sudden changes from one color or brightness level to another. This greatly reduces the amount of detail in the image and gives it a more drawn or spray-painted appearance.
And although the effect may seem complicated, once you know the steps, you can do it from start to finish in just a few minutes!
Step 1: Add a Posterize adjustment layer
Let's start by creating the initial poster effect. And to do that, all that's needed is to apply image adjustments Posterize. But to keep the effect separate from the image itself, we'll apply Posterize as an adjustment layer.
In the table Layersthe image appears on the Background layer.

Click the icon New Fill or Adjustment Layers at the bottom of the Layers panel.

Then choose Posterize from the list.

Photoshop adds a Posterize adjustment layer above the image.

And immediately, you will see the original poster effect. Next, we'll learn why the colors look the way they do and how to adjust them.

How the Posterize image adjustment process works
Let's quickly see what's happening with the Posterize tuning process. The controls for the adjustment appear in the table Properties. And here there's a single slider called Levels is set to the default value of 4.

Photoshop color channels
Levels controls the number of brightness levels in each of Photoshop's 3 color channels (Red, Green, and Blue). If switching from table Layers to the table Channelswe will see the Red, Green, and Blue channels all blending together to create the colors we see in the image.
With Levels is set to 4we will limit the image to 4 shades of red, 4 shades of green, and 4 shades of blue, for a total of 64 possible colors (4x4x4).

The lowest setting you can choose for Levels is 2which gives you just 2 shades each of red, green, and blue.

This results in the least amount of detail in the image and the strongest poster effect.

And if you drag the Levels slider all the way to the right to the maximum value of 255:

Essentially, we're turning off the Posterize adjustment and viewing the image in full color.

Switch from the Channels panel back to the Layers panel.

Find the value that works best
So low values create a much stronger poster effect. And for most images, a value between 4 and 10 works well.
The easiest way to find the best value for your image is to click on the current Levels value to highlight it. Then, use the up and down arrow keys on your keyboard to cycle through the values.
For this image, a Levels 5 value looks best.

And here is the result.

Step 2: Change blend mode to Luminosity (optional)
Note that we see some strange colors in the image, especially in skin tones. That's because we give Photoshop too few colors to work with. Depending on your image, these colors may be the effect you want as they give a more realistic poster look.
But if you want to restore the original color of the image, simply change the blend mode of the Posterize adjustment layer from Normal wall Luminosity.

Blend mode Luminosity limits the effect to luminance values only, leaving the original color unchanged. This is really a personal preference, but with this image, the original color looks better.
If you prefer a more realistic poster effect, change the blend mode back to Normal.

Step 3: Add a Levels adjustment layer
To control the effect a little better, add a Levels adjustment layer between the image and the Posterize layer.
In the Layers panel, click the layer Background to select that layer.

Then click the icon New Fill or Adjustment Layers at the bottom:

And this time select Levels.

Photoshop adds a Levels adjustment layer above the image and below the Posterize adjustment layer.

Step 4: Drag the Midtone slider
In the Properties panel, find the Midtone slider below the middle of the histogram.

Then drag the slider left or right. Dragging to the left will push the effect more into lighter tones.

And dragging the slider to the right brings out more dark tones. You don't want to pull too far in any direction. The default Midtone value is 1. This example would lower it to 0.96 just to add a little more contrast.

Click the Levels adjustment layer visibility icon to toggle and compare the effect with and without the Midtone adjustment.

Step 5: Group the two adjustment layers
At this point, if you are satisfied with the poster effect applied to the entire image, you can stop here and be done. But if you want to limit the effect to just your subject, here's how to do it.
First, you need to place your two adjustment layers into a layer group. So, in the Layers panel, click on one of the adjustment layers to select it. Then, hold down the key Shift on your keyboard and click the remaining adjustment layer to select both.

With both layers selected, click the Layers panel's menu icon:

And choose New Group from Layers.

Name the group as Posterize and click OK.

Back in the Layers panel, the adjustment layers appear inside the new Posterize group. You can rotate the group to open or close by clicking the arrow next to the folder icon.

Step 6: Turn off the group and select the image layer
Turn off the effect for a moment, just so you can see your original image, by clicking the group's display icon.

Then, click on the image layer to activate.

Step 7: Select Select Subject
We need to choose our main subject. And the fastest way is to use Photoshop's Select Subject command.
Go to menu Select in the menu bar and select Subject.

Photoshop analyzes the image and after a few minutes, a selection border will appear. Often, people want to refine selections, especially around hair, using Photoshop's Select and Mask workspace. But we don't need a perfect choice for our poster effect. Just a good enough choice is enough. And so far, Select Subject does a great job.
The article will quickly show you how to clean up any problem areas after turning the selection into a layer mask, which we'll do next.

Step 8: Select and enable the Posterize group
With the selection border in place, click the Posterize group in the Layers panel to select it. Then click that group's display icon to turn the effect back on.

Step 9: Add layer mask to group
Click the Add Layer Mask icon at the bottom of the Layers panel.

And Photoshop instantly converts the selection border into a layer mask, limiting the poster effect to the subject only.

Step 10: Clean up the layer mask if necessary
In the Layers panel, the layer mask thumbnail has been added to the group. The white area on the mask is the selected area and where the effect appears. The black area is everything outside the selection and where the effect is hidden.
If you hold down the key Alt on PC or key Options on your Mac and click the layer mask thumbnail:

You will see the mask layer itself in the document. And pay attention to how well Select Subject does, especially with a woman's hair. Hold Alt (Win) / Option (Mac) and click the layer mask thumbnail again to hide the mask and return to the image.

Paint on the layer mask to add or remove areas
But if there is any part of the subject that the Select Subject command misses, or if there is any part of the background that needs to be removed from the effect, just select the Brush Tool from the toolbar.
Then, fill the layer mask with white to add an area to the effect, or fill it with black to remove an area from the effect. Use the left and right bracket keys ( [ và ] ) on the keyboard to adjust the brush size as needed.
