# Warp Affine using R

#### Lampros Mouselimis

#### 2023-07-08

The getAffineTransform() and warpAffine() functions of the OpenImageR package is an RcppArmadillo re-implementation of existing Python Code and this vignette shows how these functions can be used from within R based on the author’s .ipynb file

    require(OpenImageR)

    path = system.file('tmp_images', 'landscape.jpg', package = "OpenImageR")

    img = readImage(path)
    print(dim(img))

    ## [1] 600 600   3

Input Image

    r = ncol(img)
    c = nrow(img)
    offset = 50

    original_points = matrix(data = c(0, 0, r, 0, 0, c),
                             nrow = 3,
                             ncol = 2,
                             byrow = TRUE)

    transformed_points = matrix(data = c(offset, 0, r, offset, 0, c-offset),
                                nrow = 3,
                                ncol = 2,
                                byrow = TRUE)

    M_aff = getAffineTransform(original_points = original_points,
                               transformed_points = transformed_points)

The following is the Affine transformation matrix,

    print(M_aff)

    ##            [,1]        [,2] [,3]
    ## [1,] 0.91666667 -0.08333333   50
    ## [2,] 0.08333333  0.91666667    0

The Affine transformation matrix can be used as input in the warpAffine() function,

    res_3d = warpAffine(img = img,
                        M = M_aff,
                        R = r,
                        C = c,
                        verbose = TRUE)

    ## time to complete : 0.0644 secs

    str(res_3d)

    ##  num [1:600, 1:600, 1:3] 0 0 0 0 0 0 0 0 0 0 ...

The next image shows the output based on the input data and parameters,

    imageShow(res_3d, clear_viewer = FALSE)

Output of Warp Affine function