FCP 7: Color Correcting Using Limit Effect

[Updated July 24, 2004, with new images and effects.]

Sometimes, you need to color correct part of an image — like change the color of a car or, um, sculpture — without changing anything else in the scene.

Final Cut makes this possible using the Limit Check feature of the Color Corrector. This article explains how.

1. Put the image you want to change on the Timeline.

 

2. Select it and apply the Color Corrector 3-way filter

 

 

3. Double-click the clip to load it into the Viewer, then click the Color Corrector 3-way tab at the top of the Viewer.

What we are going to do is to select just the color we want to change, using the Limit Effect feature, while still retaining the texture of the original image. In this case, we want to take the red of the sculpture and change it; first to make the background black and white, then, second, to change the sculpture to purple.

Here’s how:

 

4. Twirl down the small triangle at the lower left corner of the color corrector window.

 

 

5. Take the eyedropper from the lower right corner (“Select Color”) …

 

 

6. … and click near the middle of the sculpture.

 

 

7. Click just ONCE on the red key icon, just below the eyedropper tool, (“View Final/Matte/Source”). The key icon turns black and white. What we’ve done is switch the Canvas display from showing the final effect to showing the actual matte we are applying to the color selection.

 

 

Notice that the photo has been replaced by a blotchy white block against a solid black background. We have the beginnings of a key, but we still need to do more work.

 

 

8. The best way to work with any chroma-keyer is to adjust one parameter until it looks as a good as it can, then move on to the next setting. In this case, we will adjust the color slider immediately underneath the words “Limit Effect” until we get the key as solid as possible.

 

 

9. Next, turn off and on the Sat (short for “Saturation”) setting, notice the difference in the key, and select which looks the best. The two dots at the top of the Sat bar control the range of saturation being selected. The two dots at the bottom of the bar determine the amount of feathering for that saturation. Generally, I tweak the top two dots first, then tweak those on the bottom.

 

And this points out a good practice. Don’t tweak everything at once. Work with one setting until it looks as good as possible, then move on to the next setting.

 

10. Next, turn off and on the Luma (short for “Luminance”) setting and, again, pick the setting that looks the best. In this case, for this image, leaving the Luma setting off makes the best key.

 

 

11. By now you should have a reasonably good looking key. This dialog box above shows the settings I used…

 

 

…to create this key.

 

12. Next, Edge Thin should be used sparingly. In this case, Edge thinning “eats” into an edge to try to eliminate a color halo effect. In this case, adding a little edge thinning helped solidify the matte to compensate for the low resolution of the image.

 

 

13. Softening blurs the image so that the edge isn’t hard and sharp. This should be used EXTREMELY lightly — click once, maybe twice, on the right pointing arrow.The slider will barely move on the line, but that’s OK, you don’t want a lot.

 

14. You now have a key that specifically selects the red color, and ignores everything else in the picture. You have “limited” the overall effect to just one color in the shot.

 

 

To test this, drag the Saturation slider in the top half of the window all the way to the left. Notice how the sculpture has lost all it’s color?

 

 

15. Now, let’s reverse things. Click the icon farthest below the color selection magnifying glass. This inverts the selection so that everything EXCEPT the sculpture is selected.

 

 

16. With the saturation slider all the way to the left… you have an instant “Pleasantville” effect.

 

 

17. Reset the saturation slider back to the middle of the bar, grab the slider dot in the mid-gray color wheel and drag it near the blue edge of the color circle.

 

 

With the Invert button still clicked, notice how the background has taken on a decidely blue hue?

 

 

18. Now, uncheck the Invert button and notice how the sculture has taken on a more modern, happening, purple color, yet the background remains unchanged.

You can use this effect to change, or enhance the colors of anything — provided whatever you are changing is the only object in the shot that uses that specific color.

Keep in mind that DV footage has a very limited color range due to its extreme compression (see the article: Color Compression, Chroma-key and DV). If you want to improve the quality of your results, work with SD or HD footage, create your effect, then convert it into the DV format you need.

Have fun playing!