Locate needle image matrix position in a haystack_image matrix. Helper function for locate_image().

Searches the value that the needle and the haystack have in common and that appears fewest times in the haystack, and uses one of its positions as an anchor. Every candidate position of the needle is then a difference between a position of the value in the haystack and the anchor, so only those candidates have to be compared.

Usage

locate_ndl_in_hay(ndl_mt, hay_mt, exact = TRUE, timeout = 5, tol = 0)

Arguments

ndl_mt, hay_mt: A matrix
exact: A logical. Check matching exactly or not. FALSE compares sampled pixels only.
timeout: A numeric for timeout seconds.
tol: A numeric for the tolerance of the comparison, in steps of 255 grayscale levels. 0 needs an exact match. Use a positive value for an image that has been through a lossy format such as JPEG.

Value

    A numeric pair of xy location for needle image.

Examples

haystack_image <- imager::load.example("parrots")
w <- 100
h <- 50
needle_image <- crop_image(haystack_image, 129, 257, w, h)
hay_mt <- image2gray_matrix(haystack_image)
ndl_mt <- image2gray_matrix(needle_image)
(pos <- locate_ndl_in_hay(ndl_mt, hay_mt))
#> [1] 129 257

found <- crop_image(haystack_image, pos[1], pos[2], w, h)
layout(c(1:3))
plot(haystack_image)
plot(needle_image)
plot(found)