
Simply...
- Open photoshop, create 256x256 image with transparent background.
- Cut out/ add your image / text.
- Hold control, and click all layers selecting them all.
- right click -> merge layers.
- Hold control and click on the mini image of the giant layer in layer box, making a dotted selection line around your spray.
- Click on 'channels' icon next to new layer button
- Create a new channel