read_images: Read images into an array
In phenofun: Automated Processing of Webcam Images for Phenological Classification

This function reads in a set of images and returns all images as an array.

read_images(colormode = "Color", dim_images = NULL, folder, file_names,
  which_images, x = seq_len(dim_images[1]), y = seq_len(dim_images[2]),
  col_out = seq_len(dim_images[3]), col_in, sum1 = FALSE, norm_it = FALSE,
  norm_type = "sum1", colorspace = "rgb", relative = FALSE)

`colormode`	the output colormode: either "Color" (default) or "Grayscale"
`dim_images`	the dimension of the output array
`folder`	the path of the folder which contains the images
`file_names`	a vector giving the names of the input files
`which_images`	indices of the images to read, relative to `file_names`
`x`	Vector of x-coordinates to read in. Default `NULL` results in a grid of all possible values.
`y`	Vector of y-coordinates to read in. Default `NULL` results in a grid of all possible values.
`col_out`	which color-channels shall be read in?
`col_in`	which color-channels has the input image?
`sum1`	`TRUE`: Pixel intensities are normed to sum=1, i.e. relative intensities are computed, default is `FALSE`
`norm_it`	`TRUE`: Images are normed so that column, row and colour channel intensities have sum=1 or mean=0, default is `FALSE`
`norm_type`	Type of normalization, either sum of each image = 1, i.e., `"sum1"`, or mean of each image = 0, i.e., `"mean0"`, default `"sum1"`
`colorspace`	either `"rgb"` or `"hsv"`, default is `"rgb"`
`relative`	`TRUE`: If only one colour channel shall be extracted from a colour image, then this channel is returned relatively to the other two channels, default is `FALSE`.