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# This file is part of scattermore.
#
# Copyright (C) 2022-2023 Mirek Kratochvil <exa.exa@gmail.com>
# 2022-2023 Tereza Kulichova <kulichova.t@gmail.com>
#
# scattermore is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# scattermore is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with scattermore. If not, see <https://www.gnu.org/licenses/>.
#' default_kernel
#'
#' Create a nice defaulted kernel for `apply_kernel_*` functions.
#' Parameters are documented in the exported functions.
default_kernel <- function(filter, radius, sigma) {
if (!is.numeric(radius) || !is.numeric(sigma) || length(radius) != 1 || length(sigma) != 1) {
stop("parameters radius and sigma must be numbers")
}
if (radius <= 0) stop("radius must be positive")
kernel_pixels <- ceiling(radius)
size <- kernel_pixels * 2 + 1 # odd size
if (filter == "circle") {
kernel <- matrix(
pmin(1, pmax(0, -sqrt(rowSums(expand.grid(-kernel_pixels:kernel_pixels, -kernel_pixels:kernel_pixels)^2)) + radius)),
size, size
)
} else if (filter == "square") {
kernel <- matrix(1, size, size)
} else if (filter == "gauss") {
kernel <- matrix(
exp(
-rowSums(expand.grid(-kernel_pixels:kernel_pixels, -kernel_pixels:kernel_pixels)^2)
/ (sigma^2)
),
size, size
)
} else {
stop("unsupported kernel shape")
}
}
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