Shiny ImageMagick - single file

global.R

library(shiny)
library(shinyIncubator)
library(shinyAce)
options(shiny.maxRequestSize = -1)
platform <- sessionInfo()$R.version$platform
linux <- stringr::str_detect(platform, "linux")

logo <- function(img,link, height="200px") tags$a(href=link, tags$img(src=img, height=height))

sourcecode <- function(link){
    tags$a(href=link, 
           style="float:right; padding-right:10px;padding-top:10px; color:yellow; background-color:red; font-family:arial; font-size:20px",
           ">>source code<<")
}

ProgressBar <- function(session, max, message="in progress...", detail=""){
  withProgress(session, min=1, max=max, expr={
    for(i in 1:max) {
      setProgress(message = message,
                  detail = detail,
                  value=i)
      print(i)
      Sys.sleep(0.1)
    }
  })
}

server.R

shinyServer(function(input, output, session) {
  
  DONE <- reactiveValues()
  
  ## uploading ##
  output$upload <- renderUI({
    if(!is.null(input$files)){
      if(is.null(DONE[["image0"]])) return(NULL)
       actionButton("info",">>image info (see/hide)<<") 
    }else fileInput("files", "Upload a JPEG file:", multiple = FALSE)
  })
  Upload <- reactive({
     if(is.null(input$files)) return(NULL)
     input$files
  })
  output$filesInfo <- renderTable({
    Upload()
  })
  
  ## image info ##
  
  output$imageinfo <- renderUI({
    if(is.null(input$files) | is.null(input$info)) return(NULL) 
    if(input$info%%2==0) return(NULL)
    ProgressBar(session,max=30)
    files <- filesNames() 
    comm <- paste("identify -verbose", files$infile)
    info <- if(linux) system(comm, intern=TRUE) else shell(comm, intern=TRUE)   
    aceEditor("aceinfo",
              value=paste(info, collapse="\n"), 
              mode="plain_text", theme="monokai", height="200px", fontSize=14, readOnly=TRUE)
  })
  
  ## zoom ##
  output$scaleUI <- renderUI({
    if(is.null(Upload())) return(NULL)
    sliderInput("scale", "Zoom", min=10, max=200, value=100, step=2)
  })
  
  ## get file names ##
  filesNames <- reactive({
    if(is.null(input$files)) return(NULL)
    files <- Upload()
    infile <- files$datapath
    infile.path <- dirname(infile)
    infile.name <- files$name
    outfile.name <- paste0("compressed_",infile.name)
    outfile <- paste0(infile.path,"/",outfile.name)
    list(path=infile.path, infile=infile, outfile=outfile, infile.name=infile.name, outfile.name=outfile.name)
  })
  
  ## rendering original image ##
  output$image0 <- renderImage({
    if(is.null(input$files)) return(NULL)
    files <- filesNames()
    # calculate progress bar time proportional to file size
    maxprogress <- floor(file.info(files$infile)$size / 30000) + 1
    ProgressBar(session, max=maxprogress, 
      message = 'Rendering in progress',
      detail = 'This may take a while...')
    DONE[["image0"]] <- "ok"
    outfile <- files$infile
    list(src = outfile,
         alt = "This is alternate text",
         contentType="image/jpeg")
  }, deleteFile = FALSE)
  output$image <- renderUI({
    if(is.null(input$scale)) return(NULL)
    scale <- as.numeric(input$scale)
    imageOutput("image0", width=paste0(input$scale,"%"))
  })
  
  ## compression settings ##
  getCommand <- reactive({
    paste0("convert -strip -interlace Plane -gaussian-blur ", input$blur, " -quality ", input$quality, "%")
  })
  observe({ # image magick command
    updateAceEditor(session, "magick", 
                    value=getCommand(),
                    mode="r", theme="cobalt")
  })
  observe({ #  stop the app if user acts after download
    input$go
    input$blur
    input$compression
    input$tab
    deleted <- isolate(DONE[["deleted"]])
    if(is.null(deleted)) return(NULL)
    stopApp()
  })
  Compress <- reactive({ # run compression 
    input$go # makes reactivity to the go button
    files <- filesNames()
    comm0 <- isolate(getCommand())
    comm <- paste(comm0, files$infile, files$outfile)
    if(stringr::str_detect(platform, "linux")) system(comm) else shell(comm)    
  })
  
  ##  compress and render image ##
  output$cimage <- renderImage({
    files <- filesNames()
    # calculate progress bar time proportional to file size
    maxprogress <- floor(file.info(files$outfile)$size / 40000) + 1
    ProgressBar(session, max=maxprogress)
    DONE[["cimage"]] <- "ok"
    files <- filesNames()
    list(src = files$outfile,
         alt = "This is alternate text")
  }, delete=FALSE)
  output$cimageUI0 <- renderUI({
    scale <- as.numeric(input$scale)
    imageOutput("cimage", width=paste0(scale,"%"))
  })
  output$cimageUI <- renderUI({
    maxprogress <- 30 
    if(is.null(input$files)) return(NULL)
    deleted <- !is.null(isolate(DONE[["deleted"]])) 
    if(input$go==0 | deleted) return(h2("Preview will appear here"))
    ProgressBar(session,max=maxprogress)
    Compress()
    DONE[["magick"]] <- TRUE
    uiOutput("cimageUI0") # reactivity to input$scale only 
  })
  
  ## compressed image info ##
  output$cimageTableInfo <- renderTable({ 
    if(is.null(DONE[["magick"]])) return(NULL)
    input$go
    files <- filesNames()
    if(!is.null(DONE[["deleted"]])){
      tabl <- data.frame("size (Mo)"=rep("0 (deleted)",2), check.names=TRUE)
      rownames(tabl) <- c(files$infile.name, files$outfile.name)
      return(tabl)
    }
    if(!(files$outfile.name %in% list.files(files$path))) return(NULL)
    tabl <- subset(file.info(files$infile, files$outfile), select=size)
    tabl$size <- round(tabl$size/1000000,1)
    colnames(tabl) <- "size (Mo)"
    rownames(tabl) <- c(files$infile.name, files$outfile.name)
    tabl
  })
  output$cimageinfobutton <- renderUI({
    if(is.null(DONE[["cimage"]])) return(NULL)
    actionButton("cimageinfo", ">>>Image info (see/hide)<<<")
  })
  output$cimageinfo <- renderUI({
    if(is.null(input$files) | is.null(input$cimageinfo)) return(NULL) 
    if(input$cimageinfo%%2==0) return(NULL)
    ProgressBar(session,max=10)
    files <- filesNames() 
    comm <- paste("identify -verbose", files$outfile)
    info <- if(linux) system(comm, intern=TRUE) else shell(comm, intern=TRUE)   
    aceEditor("aceinfocimage",
              value=paste(info, collapse="\n"), 
              mode="plain_text", theme="monokai", height="200px", fontSize=14, readOnly=TRUE)
  })
  
  
  ## tab: Compressed Image ##
  output$tab2 <- renderUI({
    if(is.null(input$files)) return(h2("Preview will appear here"))
    input$go
    uiOutput("cimageUI")
  })
  
  ## download compressed image ##
  output$download <-  downloadHandler(
    filename = filesNames()$outfile.name, 
    content = function(file){
      file.copy(filesNames()$outfile, file)
      # delete all files after download
      file.remove(unlist(filesNames()[c("infile","outfile")]))
      DONE[["deleted"]] <- TRUE
    }
  )  
  output$downloadUI <- renderUI({
    if(is.null(DONE[["cimage"]])) return(NULL)
    downloadButton("download", label="Download")    
  })

})

ui.R

shinyUI(pageWithSidebar(
  
  headerPanel("ImageMagick compression - single JPEG file",
              tags$head(
                logo(img="http://www.imagemagick.org/image/logo.jpg", link="http://www.imagemagick.org/script/index.php"),
                sourcecode(link="https://gist.github.com/stla/7186022")
              )
  ),
  
  sidebarPanel(
    
    conditionalPanel(
      condition='input.tab=="Original image"',
      uiOutput("upload"),
      br()
    ),
    
    conditionalPanel(
      condition='input.tab=="Compressed image"',
      numericInput("quality", "compression (%)", value=80, step=2),
      numericInput("blur", "gaussian blur", value=0.05, step=0.01)
    ),
    uiOutput("scaleUI"),
    conditionalPanel(
      condition='input.tab=="Compressed image"',
      uiOutput("cimageinfobutton"),
      tableOutput("cimageTableInfo")
    )
    
  ),
  
  mainPanel(
    
    progressInit(),
    
    tabsetPanel(
      
      tabPanel("Original image", 
        tableOutput("filesInfo"),
        uiOutput("imageinfo"), 
        uiOutput("image")
      ),
      
      tabPanel("Compressed image", 
               h4("This ImageMagick command is ready to be executed:"),
               aceEditor("magick",
                         value="", 
                         mode="r", theme="cobalt", height="10px", fontSize=14, readOnly=TRUE),  
               div(class='row-fluid',
                   div(class='span6', 
                       actionButton("go", "Run this ImageMagick command")
                   ),
                   div(class='span6', 
                       uiOutput("downloadUI")
                   )
               ),
               helpText(HTML("<p> >>><a href = \"http://stackoverflow.com/questions/7261855/recommendation-for-compress-jpg-files-with-image-magick\">recommendations for JPEG recompressing</a><<<")), 
               uiOutput("cimageinfo"), 
               uiOutput("tab2")
      ),
      
      id="tab"
    )
              
  )
))