image_alpha: Add Alpha Layer to an RGB Image

In pliman: Tools for Plant Image Analysis

Add Alpha Layer to an RGB Image

Description

This function adds an alpha (transparency) layer to an RGB image using the EBImage package. The alpha layer can be specified as a single numeric value for uniform transparency or as a matrix/array matching the dimensions of the image for varying transparency.

Usage

image_alpha(img, mask)

Arguments

img	An RGB image of class Image from the EBImage package. The image must be in RGB format (color mode 2).
mask	A numeric value or matrix/array specifying the alpha layer: * If mask is a single numeric value, it sets a uniform transparency level (0 for fully transparent, 1 for fully opaque). * If mask is a matrix or array, it must have the same dimensions as the image channels, allowing for varying transparency.

Value

An Image object with an added alpha layer, maintaining the RGBA format.

Examples

if (interactive() && requireNamespace("EBImage")) {
# Load the EBImage package
library(pliman)

# Load a sample RGB image
img <- image_pliman("soybean_touch.jpg")

# 50% transparency
image_alpha(img, 0.5) |> plot()

# transparent background
mask <- image_binary(img, "NB")[[1]]
img_tb <- image_alpha(img, mask)
plot(img_tb)

}

pliman documentation built on Aug. 21, 2025, 5:46 p.m.