3b - How to Separating Colors into the Spot Channels in Adobe Photoshop?
Step 1: Make sure the Art Layer is active and no selections have been made.
Step 2: Select Color Range from the Select drop down menu.
Step 3: Adjust the Fuzziness Slider to desired amount. All other setting should appear as it does below. Since every file is different and colors vary through gamma ranges there is no set amount to adjust this to and there is no way to test this out prior to print other than on your monitor. Please verify separations are correct on your end or recreate the art in a Vector Format for easier color separations. Then click OK.
Step 4: Switch back to the Channel Pallet and fill with white or 0% of black. The outcome should appear something like this.
Step 5: Deselect and Repeat steps 1 - 4 for each Alpha Channel that was created.