Keying Green Backdrops

Written by Denny Tang






 

Identify the Green Backdrop

Before we add layer mask, we need to identify the green areas and create an black and white layer to represent the transparency of the image.

  1. Open a photo you would like to edit. Or, you may use the photo used in this tutorial (from iStockPhoto).
    Make sure that the image is in RGB color mode. To switch to RGB color mode, click on RGB Color under the Image> Mode menu.

    Image from iStockPhoto.com
    Image from iStockPhoto.com

  2. Add a Channel Mixer adjustment layer (Layer> New Adjustment Layer> Channel Mixer). In the Channel Mixer window, check the Monochrome checkbox and set the Red to 200% and the Green to -200%. Don't close the Channel Mixer window yet!
    The Channel Mixer Tool
    The Channel Mixer Tool

  3. Now drag the Constant slider towards the right until the object is a 100% white; not gray. Don't go overboard with the constant setting. If the constant is set too high, the images' edge detail will be loss.
    Editing the Constant in the Channel Mixer
    Editing the Constant in the Channel Mixer

  4. You'll notice that after apply the Channel Mixer adjustment layer, the green areas are not completely black. If we leave this alone, the greens will only be 50% transparent instead of 100% transparent. To fix this, select the Background layer and open the Hue/Saturation tool (Image> Adjustments> Hue/Saturation or Ctrl+U). In the Hue/Saturation tool, select Green from the Edit drop down menu and increase the saturation until the green areas turn black.
    Adjusting the Green Backdrop
    Adjusting the Green Backdrop


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