3D Compositing with Action > Action: Textures > Projecting Textures >
Blending Projections

Use projection blend modes to modify how you want to blend the projected image in the scene. Select a mode from the Projection Blend Mode box.

Add
  Compensates for the soft or anti-aliased edge on an object in a front and matte clip media.
Blend
  Punches the matte through the front. This blends the edge of the front clip and adds additional softness to the media. This is the default setting. Use Blend mode when you do not want any shading cast on the geometries that are receiving the projection.
Max
  Compares the RGB channels of each pixel of the front clip and the back clip individually and returns the larger of the two values.
Min
  Compares the RGB channels of each pixel of the front clip and the back clip individually and returns the smaller of the two values.
Multiply
  Multiplies the RGB channel values of corresponding pixels of the front clip and the matte clip, and normalizes the result by dividing by 256 in 8-bit mode, or 4096 in 12-bit mode. The resulting RGB channel values are assigned to the corresponding pixels in the generated clip.

Hardware limitations may prevent transparency from working properly with Multiply.

Negate
  Creates a negative-like result. Try Negate with a soft white matte with a white front clip. This mode does not use the matte or transparency in its blend.
Screen
  Multiplies the inverse of the matte clip's colours with the colours of the front clip. The resulting colour is always lighter. Screen does not work with transparency.

When using a matte, set the diffuse r, g, b channels to 0, 0, 0 in the Channel Editor for the image surface you are blending.

Simple Add
  Punches the matte through the front using more softness than Blend mode. Simple Add mode is similar to Add but includes transparency.
Spotlight
  Creates a slide projector effect. This mode does not use the matte or transparency and decreases system performance.
Spotlight Blend
  Creates an effect where black areas of the front disappear. This mode does not use the matte or transparency; it works well with a clip on which an object is surrounded by black.
Subtract
  Subtracts the RGB channel values of the pixels in the matte clip from the RGB channel values of the pixels in the front clip and assigns the result to the RGB channel values of the pixel in the result.

If an RGB channel value from the matte clip is larger than the corresponding channel value in the front clip, yielding a negative result, that result is clamped at 0 (black).