hann (version 1.2)

binarize: Helper Function to Prepare Data From Images

Description

Take one or more images coded as numeric values (pixels) and return them coded as -1 or +1 depending on a threshold value.

Usage

binarize(x, threshold = median(x))

Value

an object with integers (-1/1) with the same attributes (dim, names, etc.) than the input object x.

Arguments

x

a vector or a matrix of numeric values.

threshold

a numeric value: values in x below (or equal) to this threshold are coded -1, values above are coded +1.

Details

It is recommended to check that the default of the argument threshold is appropriate or not. For instance, if an image has many pixels dark and a few light, this default might not be a good choice.

If the default is a good choice (e.g., good balance between the dark and light pixels), it can be applied globally or separately for each image. Suppose the images (patterns) are arranged along the rows of a matrix X, the binarization can be done either with:

xi <- t(apply(X, 1, binarize))

where the threshold might be different for each image, or with xi <- binarize(X) in which case the threshold will be the same for all images.

See Also

hann

Examples

## a plus (+) sign on a 3x3 grid:
x <- matrix(runif(9, 150, 255), 3, 3)
## make the corners lighter to draw the "+":
x[c(1, 3, 7, 9)] <- runif(4, 0, 20)
x <- round(x)
xi <- binarize(x)
## compare:
xi; x
layout(matrix(1:2, 1))
image(x, asp = 1, main = "Original image")
image(xi, asp = 1, main = "Binarized image")
layout(1)