R语言中更改图的大小比例

基础知识：
像素数：图片上的最小成像单位的数目。评价一个设备的像素值，一般使用宽高像素的乘积表示，如1000px * 1500 px
尺寸：指图像打印后的物理尺寸，一般用厘米/米或者（英）寸表示,1英寸（inche）=2.54厘米
分辨率：单位尺寸下像素点的数目，越高图像越细腻。计算方式为 分辨率=像素数/尺寸，是真正衡量设备清晰度的指标，单位一般为像素/英寸或者像素/厘米。
容量：图像文件的存贮空间，也就是文件的大小，一般以Kb和Mb来表示。

ps:平时所说的1200万像素的手机，是指该手机的像素数。

在R绘图中也需要调整最后图片的上述参数。一般我们使用一下函数对图片进行导出:

png()  #支持调整px或inche等
tiff() #支持调整px或inche等
pdf() #仅支持调整inche等
ggsave() #支持ggplot对象的输出，支持调整 px/inche/dpi
graph2pdf() #export系列，这里同pdf()

这里也写了一个shiny程序用于手动导出png或pdf

message(.libPaths())
.libPaths("/home/whq/my_R_package")
library(shinydashboard)
library(shiny)
library(ggplot2)
library(dplyr)
library(pheatmap)
library(grid)
library(export)
library(ggplotify)
library(bs4Dash)
plot_dir<-list.files("plot.file/",pattern = "rds|RDS")


ui<-dashboardPage(
  header = dashboardHeader(title = "Plot Output"),
  sidebar = dashboardSidebar(
    sidebarMenu(
      menuItem("Plot png",tabName = "plot_png"),
      menuItem("Plot pdf",tabName = "plot_pdf")
    )
  ),
  body = dashboardBody(
  tabItems(
    tabItem(tabName = "plot_png",
            fluidRow(
              wellPanel(
                uiOutput("filename_png"),
                numericInput("plot_width",label = "Width OF Plot(px)",min = 400,max = 2500,step = 100,value = 1000),
                numericInput("plot_height",label = "Height OF Plot(px)",min = 400,max = 2500,step = 100,value = 1000),
                numericInput("plot_resolution",label = "Resolution OF Plot(dpi)",min = 100,max = 1000,step = 100,value = 100),
                textInput("download_png_name",label = "Name of Downloaded File",value = "download png"),
                downloadButton("download_png")
              )%>%column(3,.),
              uiOutput("plot_output_ui")%>%box(collapsible = T,width = 12,maximizable = T)%>%column(9,.)
            )
    ),
    tabItem(tabName = "plot_pdf",
            fluidRow(
              wellPanel(
                uiOutput("filename_pdf"),
                numericInput("plot_width_pdf",label = "Width OF Plot(px)",min = 400,max = 2500,step = 100,value = 1000),
                numericInput("plot_height_pdf",label = "Height OF Plot(px)",min = 400,max = 2500,step = 100,value = 1000),
                numericInput("plot_resolution_pdf",label = "Resolution OF Plot(dpi)",min = 100,max = 1000,step = 100,value = 100),
                textInput("download_pdf_name",label = "Name of Downloaded File",value = "download pdf"),
                downloadButton("download_pdf")
              )%>%column(3,.),
              uiOutput("plot_output_ui_pdf")%>%box(collapsible = T,width = 12,maximizable = T)%>%column(9,.)
            )
    )
  )
  )
)

server<-function(input,output){
  
#png
  if(T){
    output$filename_png<-renderUI(
      {
        selectInput("filename_input_png","Select a plot",choices = structure(paste("plot.file/",plot_dir,sep = ""),names=plot_dir))
      }
    )
    plot_input_png=reactive({
      a=readRDS(input$filename_input_png)
      if(class(a)=="pheatmap"){
        a=as.ggplot(a)
      }
      return(a)
    })
    
    output$plot_output_ui<-renderUI(
      {
        plotOutput("plot_output",width = input$plot_width,height = input$plot_height)
      }
    )
    
    #细节操作，在renderplot中正常情况下无法使用reactive的值，因此想办法构建一个reactive将renderplot再包住
    observeEvent(input$plot_resolution,{
      output$plot_output<-renderPlot(
        {
          plot_input_png()
          
        },res =input$plot_resolution
      )
      
    })
   
    output$download_png<-downloadHandler(
      filename = paste(input$download_png_name,".png",sep = ""),
      content = function(file){
        ggsave(file,plot_input_png(),width = input$plot_width,height = input$plot_height,units = "px",device = "png",dpi = 100)
      }
    )
  }
#pdf
  if(T){
    output$filename_pdf<-renderUI(
      {
        selectInput("filename_input_pdf","Select a plot",choices = structure(paste("plot.file/",plot_dir,sep = ""),names=plot_dir))
      }
    )
    plot_input_pdf=reactive({readRDS(input$filename_input_pdf)})
    
    
    output$plot_output_ui_pdf<-renderUI(
      {
        plotOutput("plot_output_pdf",width = input$plot_width_pdf,height = input$plot_height_pdf)
      }
    )
    
    #细节操作，在renderplot中正常情况下无法使用reactive的值，因此想办法构建一个reactive将renderplot再包住
    observeEvent(input$plot_resolution_pdf,{
      output$plot_output_pdf<-renderPlot(
        {
          plot_input_pdf()
          
        },res =input$plot_resolution_pdf
      )
      
    })
    #以300dpi换算，分辨率=像素/尺寸
    output$download_pdf<-downloadHandler(
      filename = function(){
        paste(input$download_pdf_name,"-",round(input$plot_width_pdf,digits = 2),"X",round(input$plot_height_pdf,digits = 2),"_px",".pdf",sep = "")
      },
      content = function(file){
        ggsave(file,plot_input_pdf(),width =input$plot_width_pdf,height = input$plot_height_pdf,device = "pdf",units = "px",dpi = 100 )
      }
    )
  }
  
}

shinyApp(ui,server)

image.png