Comparing images by subtracting pixels

subtract_distance.R

library("EBImage")

resize_to_smallest <- function(x, y) {
    dx <- dim(x)
    dy <- dim(y)
    w <- min(dx[1], dy[1])
    h <- min(dx[2], dy[2])
    list(x = EBImage::resize(x, w, h),
         y = EBImage::resize(y, w, h))
}

subtract_distance <- function(x, y)
    UseMethod("subtract_distance")

subtract_distance.Image <- function(x, y) {
    if (is.character(y) && file.exists(y))
        y <- readImage(y)
    stopifnot(inherits(y, "Image"))
    if (!identical(dim(x), dim(y)))
        xy <- resize_to_smallest(x, y)
    else xy <- list(x, y)
    sum(EBImage::imageData(xy[[1]] - xy[[2]]) != 0) / prod(dim(xy[[1]]))
}

subtract_distance.character <- function(x, y) {
    stopifnot(file.exists(x))
    if (!inherits(y, "Image")) {
        stopifnot(inherits(y, "character"))
        stopifnot(file.exists(y))
    }
    x <- readImage(x)
    y <- readImage(y)
    subtract_distance.Image(x, y)
}

isSimilar2 <- function(x, y, threshold = 0.001, exact = FALSE) {
    if (exact) threshold <- 0
    if (threshold > 1) threshold <- 1
    if (threshold < 0) threshold <- 0
    subtract_distance(x, y) <= threshold
}