Plotting user selected images in Shiny - r

Question

This is my first attempt at creating a Shiny app so I wanted to do something very simple: use fileInput so the user can select an image on their computer and then renderImage to plot the image.
library(shiny)
# Define UI for application that draws a histogram
ui <- fluidPage(
# Application title
titlePanel("plot image"),
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
fileInput("image",
"Select your image:", placeholder = "No file selected")
),
# Show a plot of the generated distribution
mainPanel(
plotOutput("photo")
)
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
output$photo <- renderImage({
img <- load.image(input$image)
plot(img)
})
}
# Run the application
shinyApp(ui = ui, server = server)
However, when I try to load an image with this I get an error: invalid filename argument.
Ultimately I would like to integrate selectInput the choices option would have a few default images as well as those the user uploaded with fileInput but I feel that I'm already getting ahead of myself on that.
UPDATE 1:
library(shiny)
library(ggplot2)
library(imager)
# Define UI for application that draws a histogram
ui <- fluidPage(
# Application title
titlePanel("plot images"),
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
fileInput("image",
"Select your image:", placeholder = "No file selected")
),
# Show a plot of the generated distribution
mainPanel(
plotOutput("photo")
)
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
output$photo <- renderPlot({
# Ensure the values for 'image' are available
# If not, the operation is stopped by raising a "silent" exception
req(input$image)
# Get edges of image with imager::cannyEdges
img <- cannyEdges(input$image)
# img is now a logical array with 4 dimensions but we only want 2 - discard two of the dimensions
img <- img[, , 1, 1]
# Convert the matrix into a list of coordinates
coords <- which(img, arr.ind = T)
# Turn the coordinates into a dataframe
df <- data.frame(x = coords[, 1], y = coords[, 2])
# Plot the coordinates
ggplot(df, aes(x, -y)) +
geom_point()
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 1

See ?fileInput. If "image" is the id, then the path to the uploaded file is input$image$datapath, not input$image.
So you can do something like:
output$photo <- renderImage({
req(input$image)
list(src = input$image$datapath, alt="alternative text")
})
and in ui,
imageOutput("photo")

Answer 2

I encountered the same issue and solved. the image can't be loaded is because the input$image doesn't just give the filename you want, but also give more information. That make it a named list rather than a single value. Maybe you can try as following in your first case.
server <- function(input, output) {
output$photo <- renderImage({
img <- load.image(input$image[[4]])
plot(img)
})
}
Hope it works.