Image output

10.20.050.450.85

The renderImage() and imageOutput() functions can be used to display any image files on the client. This is in contrast to the renderPlot() and plotOutput() functions, which are used for images created by R's usual plot rendering device.

In the upper image, image1, a new image file is created each time the slider changes, and the deleteFile=TRUE argument tells the server to delete the temporary iamge file after it's sent to the client.

This technique can be also used for pre-rendered images. The lower image, image2 sends pre-rendered images to the client. In this case the deleteFile=FALSE argument is used so that the image files aren't deleted after being sent to the client.

show with app 
library(png) # For writePNG function

# Return a matrix with 2d guassian distribution
gauss2d <- function(x, y, r = 0.15) {
  exp(
    -((x - 0.5)^2 + (y - 0.5)^2) /
    (2 * r^2)
  )
}

function(input, output, session) {

  # image1 creates a new PNG file each time Radius changes
  output$image1 <- renderImage({
    # Get width and height of image1
    width  <- session$clientData$output_image1_width
    height <- session$clientData$output_image1_height

    # A temp file to save the output.
    # This file will be automatically removed later by
    # renderImage, because of the deleteFile=TRUE argument.
    outfile <- tempfile(fileext = ".png")

    # Generate the image and write it to file
    x <- matrix(rep((0:(width-1))/(width-1), height), height,
                byrow = TRUE)
    y <- matrix(rep((0:(height-1))/(height-1), width), height)
    pic <- gauss2d(x, y, input$r)
    writePNG(pic, target = outfile)

    # Return a list containing information about the image
    list(src = outfile,
         contentType = "image/png",
         width = width,
         height = height,
         alt = "This is alternate text")

  }, deleteFile = TRUE)


  # image2 sends pre-rendered images
  output$image2 <- renderImage({
    if (is.null(input$picture))
      return(NULL)

    if (input$picture == "face") {
      return(list(
        src = "images/face.png",
        contentType = "image/png",
        alt = "Face"
      ))
    } else if (input$picture == "chainring") {
      return(list(
        src = "images/chainring.jpg",
        filetype = "image/jpeg",
        alt = "This is a chainring"
      ))
    }

  }, deleteFile = FALSE)
}