### Overlay

Category

Rendering

Function

Overlays one image with another.

Syntax

    combined = Overlay(overlay, base, blend);

Inputs

Name | Type | Default | Description
--- | --- | --- | ---
`overlay` | image | none | overlay image
`base` | image | none | base image
`blend` | scalar, vector, field, or string | .5 | 0: for base image only 1: for overlay image only

Outputs

Name | Type | Description
--- | --- | ---
`combined` | image | combined image

Functional Details

`overlay` | is the overlay image.
`base` | is the base image under `overlay`.

`blend`

determines how the module combines the two images and what the output image will be. If the parameter is:

- a scalar value: the resulting image (`combined`) is equal to

      ((1 - blend) × base) + (blend × overlay)

- a vector or string: this value will be interpreted as an RGB color. The `combined` image is the base image except for the pixels where the base image is equal to `blend`. These pixels will be taken from the overlay image. This specification allows you to perform chromakeying.

  Two pixels are considered to have the same color if the corresponding component colors (i.e., red, green, blue) of one are each within 0.1% of the other.

  The `blend` can also be specified (in a string) as one of the standard X Window System** colors (see Color).

- a field of position-dependent data: each data value in the field is used as a blending value to overlay the two pixels (one from each image) corresponding to that position. That is, the blending is pixel by pixel. The "blending" field must have a grid that is compatible with both the overlay and the base image.

  The `blend` values in the field must be scalar values between 0.0 and 1.0.

Notes:

1. The images `base` and `overlay` must be the same size and have the same grid positions. The "colors" component must be dependent on "positions." The `base` and `overlay` images must both have the same partitioning (or none).

2. To add two images together, or subtract one from the other, use the Compute module. First mark the "colors" component in each image (with the Mark module), then, use Compute to perform the desired operation on each. Finally, use Unmark to return the modified data to the "colors" component.

Components

Modifies the "colors" component. All other input components are propagated to the output.

Example Visual Program

    UsingOverlay.net

See Also

Arrange, Color, Compute, Display, Render

[ OpenDX Home at IBM | OpenDX.org ]