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This chapter is from the book

This chapter is from the book

Color Matching Using Channel Isolation

Very often, you will have two images from the same location that are not color matched. By looking at the individual color channels in the Viewer, you can easily color match these types of shots. Once again, I've done most of the setup work for you with the color2.shk script.

  1. Choose File > Open Script and click No when prompted to save the current script.
  2. Select the color2.shk script from the Lesson03/scripts folder.

    You'll see a composite of a lifeguard tower in the center of a beach with a definite mismatch in color. Take a look at the elements.

  3. View the beach_ws and beach_cu clips.

    These are two shots of the beach with different framing and color correction. Now, take a look at the components of the composite.

  4. View each node of the tree starting with RotoShape1 and ending with Over1.

    The beach_cu clip has a RotoShape to cut it out and a Move2D to match the size and position to the beach_ws clip. The modified beach_cu is then placed on top of beach_ws with an Over. To fix this color mismatch, you can use a Mult function.

  5. Insert a Mult node between Move2D1 and Over1.
  6. Expand the Color channels by first clicking on the + next to the Color parameter and then the + next to the R button.
  7. In the Viewer, look only at the red channel. By isolating individual color channels, it is easier to match the colors.
  8. Adjust the red slider until the lifeguard cutout matches the background.

    You may find it difficult to match the two images exactly using the slider. You can adjust the red parameter with more accuracy by using the virtual sliders, which change the value interactively and give you finer control—left-drag lowers the value, right-drag raises the value. The virtual sliders are activated when you Ctrl-drag in the red parameter box.

  9. Adjust the red virtual slider.
  10. In the Viewer, look only at the green channel.
  11. Adjust the green parameter by using the virtual sliders.
  12. In the Viewer, look only at the blue channel.
  13. Adjust the blue parameter until the lifeguard cutout matches the background.
  14. Now look at the RGB channels in the Viewer at the same time.

    The lifeguard tower is now perfectly matched (depending on your standards) to the background. Another way to color match the two shots would be with the ColorMatch node, explained in the following section.

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