# Working with Composite Modes

This chapter introduces advanced composting techniques. You'll create and animate a sophisticated logo for the production company that produced "The Midnight Sun," Grace Films. You will also create two more composites for use within the movie. A discussion of composite modes begins this chapter.

Composite modes allow you to choose different ways you can combine images. Used in layered effects, they change how two or more images are combined into one image. Changing a composite mode changes how the pixel values are to be mixed between two or more images using different combinations of pixel values above and below each other in the Timeline's video tracks. Each composite mode uses a different mathematical formula that defines how pixel values in the affected layer are combined with the layer or layers beneath it. The resulting pixels are the composite you see.

To select a Composite mode other than the default mode, which is Normal, Ctrl-click in the Timeline the clip you want to affect, and choose the new mode from the resulting pop-up menu, as shown in Figure 13.1. Alternatively, you can select a clip, select Modify, Composite Mode, and then choose from the resulting submenu. You have 13 different choices.

• Normal A linear mix of layers. This is the default mode. To mix layers, you must lower the opacity of the upper layer to see a mix of it with the layers beneath it. This looks the same as a dissolve and can be keyframed to act much like one.

• Add Composites the color values of the affected clip with the ones in the layer or layers below it. The resulting image is brighter, but no pixels exceed absolute white. Selecting this mode adds a pixel's value in the affected layer to those directly beneath it.

• Subtract Almost the opposite of Add. Composites the color values of the affected clip with the values in each pixel below it. You can darken the composite using this mode, but you can't go below absolute black.

• Difference Similar to Subtract, but the resulting value of the each pixel is made positive and is an absolute value of this subtraction.

• Multiply Calculates each pixel change in the resulting composite by multiplying each color channel's value by the corresponding one beneath it and then dividing this result by 255. Using this mode always darkens the image if it is light. This can be used to remove white areas of an image, leaving the dark areas to superimpose.

• Screen Black or dark pixels are not added to the overlay. This composite mode inverts the brightness values of the colors in the layers and then multiplies the results. It's sort of like the opposite of Multiply: It loses the dark areas instead of the light areas.

• Overlay Analyzes the values of the pixels' colors and applies Screen only to values greater than 128. If the value is less than 128, the Multiply composite mode is applied.

• Hard Light Combines parts of Screen and Multiply with the approach of Soft Light. Like Soft Light, the action changes depending on the value of the underlying pixel. If the underlying pixel is brighter than 50% gray, the overlay pixel value is processed as if the two layers were combined using Screen mode. If the underlying pixel value is below 50% gray, the two layers are processed together as if the layers were combined with Multiply mode. The darker pixels darken. The result is usually quite dramatic. Hard Light simulates shining a harsh light (whose color is the light color or filtered output) on the source image. The source image and the light or filtered output contribute roughly equal amounts of detail to the final output.

• Soft Light Similar to Hard Light, but the lighting effect is more diffused light, as if a "soft light" is hitting the image. Soft Light either darkens or lightens depending on the underlying color. If the underlying color is lighter than 50% gray, the value of the overlay pixel is added to the underlying pixel. If the underlying color is darker than 50% gray, the overlay pixel is subtracted from the underlying pixel. Some parts of the image lighten and some parts darken for a generally pleasing result that simulates shining a diffuse light (whose color is the light color or filtered output) on the source image. Most of the detail in the final output comes from the source image.

• Darken Compares the values of the upper pixel with the lower one and selects the darker of the two to show in the resulting composite. The resulting image is always darker.

• Lighten Similar to Darken, but the opposite happensthe lighter value is displayed. The resulting image is always lighter.

##### Figure 13.1. Changing a composite mode by Ctrl-clicking a clip in the Timeline.

Two types of travel mattes also are available. A matte is a solid background color that is to be removed later and replaced with an image beneath it. It's as if a matte is a "hole cutter " in your image that defines an area that becomes transparent and thus reveals the image below it.

Mattes can also have semitransparent effects, depending on the brightness values of a given portion of them. Travel mattes usually (but not always) involve three tracks of video. The composite's foreground is the upper track, and the composite's background is the lower of the three tracks. The clip used as the matte is the middle track.

You change the composite mode to one of the two travel mattes to the uppermost track. The resulting composite uses the center track as the matting information to calculate the combination of images.

The two types of travel mattes are as follows :

• Travel Matte Alpha Adds a matte to the selected clip. In the case of Travel Matte Alpha, RGB values are ignored, and the selected clip's alpha channel is used to create the matte (you must have an alpha channel in the clip).

• Travel Matte Luma This matte is determined by averaging the RGB values contained in the clip. It changes the image to shades of gray and then uses this resulting image to define the matte. The different shades of gray determine the amount of transparency used in the resulting composite.

Figure 13.2 shows a two-layer Travel Matte Luma effect. The default "fill" is black because there is no bottom layer of video. Only the fire in the logo is shown. The white areas of the matte on V1 determine what part of the upper track is seen. The shades of gray in the matte shape file effectively soften the edges around the "hole" it cuts in the video. "FireGlowMatte.tga" was moved up, revealing an alpha track that was ignored. The V2 picture track has a Travel Matte Luma applied to it.

##### Figure 13.2. A Travel Matte Luma revealing just the fire in the original picture.

Jerry Hofmann on Final Cut Pro 4
ISBN: 735712816
EAN: N/A
Year: 2005
Pages: 189