scripts/builtin/img_crop.dml

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# The img_crop-function is an image data augmentation function. It cuts out a subregion of an image.
#
# INPUT:
# ----------------------------------------------------------------------------------------
# img_in    Input matrix/image
# w         The width of the subregion required
# h         The height of the subregion required
# x_offset  The horizontal coordinate in the image to begin the crop operation
# y_offset  The vertical coordinate in the image to begin the crop operation
# ----------------------------------------------------------------------------------------
#
# OUTPUT:
# --------------------------------------------------------------------------------------------------
# img_out  Cropped matrix/image
# --------------------------------------------------------------------------------------------------

m_img_crop = function(Matrix[Double] img_in, Integer w, Integer h, Integer x_offset, Integer y_offset) return (Matrix[Double] img_out) {
  # crop - cut out a subregion of an image. Adapted from image_utils.dml
  orig_w = ncol(img_in)
  orig_h = nrow(img_in)

  start_h = (ceil((orig_h - h) / 2)) + y_offset
  end_h = (start_h + h - 1) 
  start_w = (ceil((orig_w - w) / 2)) + x_offset
  end_w = (start_w + w - 1) 

  if((start_h < 0) | (end_h > orig_h) | (start_w < 0) | (end_w > orig_w)) {
    print("Offset out of bounds! Returning input.")
    img_out = img_in
  }
  else {
    mask = matrix(0, rows=orig_h, cols=orig_w)
    temp_mask = matrix(1, rows=h , cols=w )
    mask[start_h:end_h, start_w:end_w] = temp_mask
    mask = matrix(mask, rows=1, cols=orig_w * orig_h)
    img_out = matrix(removeEmpty(target=(matrix(img_in+1, 1, orig_w * orig_h)), margin="cols", select=mask) - 1, h, w)
  }
}