打印多个光栅图像时填充空白

因为 asp=1 图像保持了图像的原始纵横比 512:768 在你的例子中。相反,默认打印设备的纵横比似乎接近 1:1 . 这不匹配,导致空白空间。

1. asp=NA 通过扭曲图像,让图像使用设备的整个空间。

2. width 和 height dev.new() . 例如:

   library(EBImage)
   library(png)
   png <- readPNG(system.file("images", "sample-color.png", package="EBImage"))
   dev.new(width=4.5, height=8)
   par(mfrow=c(2,2), mar=c(0, 0, 1, 0))
   for(i in seq_len(4)){
       plot.new()
       plot.window(xlim=c(0, 1), ylim=c(0, 1), asp=1)
       rasterImage(png, 0, 0, 1, 1)
       title(paste0("Image ", i))
   }
   

png 包不是必需的,下面是另一个利用 EBImage . 除非有意变换图像,否则EBImage将保持纵横比。

此解决方案需要更多的工作来放置打印标签 text() 但增加的成本可能会被更大的灵活性所抵消。

# Starting from EBImage
  library(EBImage)
  fn <- system.file("images", "sample-color.png", package="EBImage")

# Single EBImage object with same four pictures
  pngs <- readImage(rep(fn, 4))

# Select spacing and margin for EBImage display/plot function
  spacing <- 50 # pixels between images
  margin <- 50 # pixels around edge
  nx <- 2 # number of rows for composite
  ny <- 2 # number of columns for composite
  dm <- dim(pngs)
  nframes <- dm[length(dm)]
  yadj <- -0.2 # offset for labels in y direction

# Indices, coordinates, and labels for text
  index <- seq_len(nframes)
  ix <- (index - 1)%%nx
  iy <- (index - 1)%/%nx
  xx <- ix*(dm[1] + spacing) + dm[1]/2
  yy <- iy*(dm[2] + spacing)
  labs <- sprintf("%s. Image %d", letters[index], index)

# Plot composite and add "titles" with text() function
  plot(pngs, all = TRUE, nx = nx, margin = margin, spacing = spacing)
  text(xx, yy, labs, adj = c(0.5, yadj))

# To eliminate ANY space in the composite make the following
# changes and re-run the code from "# Indices, coordinates..."
  spacing <- 0
  margin <- 0
  yadj <- 1.2
  dev.new(width = nx*dm[1]/200, height = ny*dm[2]/200) # 200 dpi image