img_contrast returns the RMS contrast of an image img. A higher value indicates higher contrast.

img_contrast(img)

## Arguments

img An image in form of a matrix or array of numeric values. Use e.g. img_read() to read an image file into R.

## Value

a numeric value (RMS contrast)

## Details

The function returns the RMS contrast of an image img. The RMS contrast is defined as the standard deviation of the normalized pixel intensity values. A higher value indicates higher contrast. The image is automatically normalized if necessary (i.e., normalization into range [0, 1]).

For color images, the weighted average between each color channel's values is computed.

## References

Peli, E. (1990). Contrast in complex images. Journal of the Optical Society of America A, 7, 2032--2040. doi:10.1364/JOSAA.7.002032

img_read, img_complexity, img_self_similarity, img_simplicity, img_symmetry, img_typicality,

## Examples

# Example image with relatively high contrast: berries
berries <- img_read(system.file("example_images", "berries.jpg", package = "imagefluency"))
#
# display image
grid::grid.raster(berries)
#
# get contrast
img_contrast(berries)

# Example image with relatively low contrast: bike
bike <- img_read(system.file("example_images", "bike.jpg", package = "imagefluency"))
#
# display image
grid::grid.raster(bike)
#
# get contrast
img_contrast(bike)