Code to render facial image using R graphics device and magick library

shiny-vision-facial-image.R

# We first create an image pointer with image_read(/path/to/image)
photo = magick::image_read(values$file_path)
# obtain photo dimensions
photo_info = magick::image_info(photo)
height = photo_info$height
max_height <- 400  # this variable is used for height parameter within renderImage()
rescale_lwd <- 2/max_height * height  # rescale our line widths when drawing

# draw original image without analysis features
magick::image_draw(photo)

########################
#### FACE DETECTION ####
########################
facial_features_found <- !is.null(values$img_res$fdBoundingPoly$vertices)
if (facial_features_found) {
  # loop through each face found with mapply
  mapply(bboxes = values$img_res$fdBoundingPoly$vertices,  # bounding boxes
         lbl_id = c(1:length(values$img_res$fdBoundingPoly$vertices)),  # label by number
         facial_pts = values$img_res$landmarks,  # landmark points
         function(bboxes, lbl_id, facial_pts) {
          # Draw bounding box polygons for each face found
           polygon(x = bboxes[[1]], y = bboxes[[2]], border = 'red', 
                   lwd = rescale_lwd)  # rescaled line width
           # Draw label id's on top of each bounding box
           text(x = bboxes[[1]][[3]], y = bboxes[[2]][[3]], 
                labels = as.character(lbl_id),  # label each image with an id
                offset = 1,
                cex = 3,  # text magnified by this factor relative to default
                col = "white")
           # Draw facial landmark points
           points(x = facial_pts$position$x,  # plot the x coordinates of facial landmarks
                  y = facial_pts$position$y,  # plot the y coordinates of facial landmarks
                  col = "green", 
                  lwd = rescale_lwd, 
                  pch = 3)
         })
} else {  # else, no features were detected
  text(x = width/2, y = height/2, labels = "No features detected", col = "red",
       offset = 1, cex = 5)
}
# save image with graphics output drawings to image pointer
photo = magick::image_capture()
dev.off()
# store it into a temporary file for imageOutput UI
tmpFile <- image_write(photo, tempfile(fileext='jpg'), format = 'jpg')