Step 1
Open your image in Adobe Photoshop and make sure it is on a separate layer. You can easily achieve this by duplicating layer. Right-click on your image in Layers window and press Duplicate Layer.
Step 2
From the menu select: Image > Adjustments > Posterize
Step 3
Adjust Level of posterize effect somewhere between 2-5, in this tutorial I chose 4.
Step 4
Next we are going to adjust threshold. From the menu follow this patch: Image > Adjustments > Threshold
Step 5
Pick a Threshold level which preserves most detail.
Step 6
If needed use Eraser tool to get rid of the noise in the background.
Step 7
Now you need to save your image as JPEG file. File > Save as. From Format selection choose JPEG, and press Save.
Done! You are ready to print your stencil.