Chroma Keying and Working with Green Screens > Refining Your Key > Adjusting the Luminance of the Key >

# Using the Luminance Curves

When you create a matte for the front clip, the Keyer automatically creates a matte for the back clip to specify which part of the back clip is used for the composite. By default, the back matte is the inverse of the front matte.

You can adjust the luminance of the front matte and back matte separately in the Blending menu in the Result node in the schematic. For example, increase the luminance of the back matte so that more of the back clip shows through at the edges of the key. This creates a better blend at the edges of the key.

To adjust the luminance curve:

1. Double-click the Result node in the schematic.

   The Luminance curve appears.

   (a) Front matte curve(b) Back matte curve(c) Front/Back box

2. Use the Viewing box to select the image you want to view as you adjust the curves.

   Select: | To view:
   --- | ---
   Result | The composite clip.
   Matte | The front matte. You cannot see changes made to the back matte when this view is selected.
   Bmatte | The back matte. You cannot see changes made to the front matte when this view is selected.
   Comp | The composite with a coloured background. The default colour is black. To select a different colour, click the colour pot to the right of the Comp button. The colour picker appears.

3. To adjust the luminance curve for the front matte, select Front from the Front/Back box. To adjust the back matte curve, select Back. Alternatively, click a curve to select it.

   The selected curve changes to white.

   (a) 255 (White)(b) Output (remapping of luminance values)(c) 0 (Black)(d) 0 (Black)(e) Input (current luminance values)(f) 255 (White)

4. Click a point to display its tangent handle and drag the handle to adjust the curve. Use other modes in the Tools box to further adjust the curve, adding or deleting points or breaking tangent handles, as needed.

#### Related Information

- Adjusting the Luminance of the Key
- Chroma Keying and Working with Green Screens