Author: Richard Cotton
Date: 2024-04-09

# Scaling and Clipping Images

#### Richard Cotton

#### 2024-04-09

## Scaling Images

By default, images (such as JPEG, PNG, BMP, SVG) that are placed in panels are not scaled. This section demonstrates the four different scaling options available.

Here’s a multi-panel figure with four panels, to contain the images. In each case, we’ll use the copy of the R logo contained in the multipanelfigure package. This is a PNG file, 800 pixels wide and 700 pixels high, with a resolution of 300 dots per inch (DPI). That gives it a native size of 2.67” by 2.33”.

    library(multipanelfigure)
    figure <- multi_panel_figure(
      width = c(1, 5),
      height = c(1, 1, 4),
      unit = "inches")
    r_logo <- system.file("extdata/Rlogo.png", package = "multipanelfigure")

By default, the image is not rescaled, which means that only the central part of the image is displayed.

    (figure %<>% fill_panel(r_logo))

    ## Setting row to 1

    ## Setting column to 1

By setting `scaling = "stretch"`, all the image is displayed, fitting the panel exactly, but the height-to-width ratio had been altered, distorting the image.

    (figure %<>% fill_panel(r_logo, scaling = "stretch"))

    ## Setting row to 1

    ## Setting column to 2

Setting `scaling = "fit"` means that the image is shrunked or grown so that it just fits inside the panel without the height-to-width ratio being distorted.

    (figure %<>% fill_panel(r_logo, scaling = "fit"))

    ## Setting row to 2

    ## Setting column to 1

Setting `scaling = "shrink"`, works the same way as `scaling = "fit"` when the image is larger than the panel.

    (figure %<>% fill_panel(r_logo, scaling = "shrink", row = 3, column = 1))

If the image is smaller than the panel, `scaling = "shrink"` works like `scaling = "none"`.

    (figure %<>% fill_panel(r_logo, scaling = "shrink", row = 2:3, column = 2))

## Clipping Plots and Images

By default, plots and images are clipped so that they don’t overrun the panel that they were put in. (See, for example, Panel A in the previous plot.) To demonstrate the effect of clipping, let’s use a 3 by 3 multi-panel figure, and fill all but the centre panel.

    library(grid)
    figure2 <- multi_panel_figure(
      width = rep.int(1.25, 3),
      height = rep.int(1.25, 3),
      unit = "inches")
    rhino <- system.file("extdata/rhino.jpg", package = "multipanelfigure")
    for(position in list(c(1, 1), c(1, 2), c(1, 3), c(2, 1), c(2, 3), c(3, 1), c(3, 2), c(3, 3)))
    {
      figure2 %<>%
        fill_panel(
          rectGrob(gp = gpar(fill = "#91A45E")),
          row = position[1],
          column = position[2])
    }
    figure2

When we try to display the rhino, only the central part of the image is shown, since there is no rescaling, and the panel isn’t big enough.

    (figure2 %>% fill_panel(rhino))

    ## Setting row to 2

    ## Setting column to 2

To turn off clipping, set `panel_clip = "off"`. This time the complete image of the rhino is displayed, overrunning the other panel regions.

    (figure2 %>% fill_panel(rhino, panel_clip = "off"))

    ## Setting row to 2

    ## Setting column to 2