slideView

Two images are overlaid and a slider is provided to interactively compare the two images in a before-after like fashion. img1 and img2 can either be two RasterLayers, two RasterBricks/Stacks or two character strings. In the latter case it is assumed that these point to .png images on the disk.

NOTE: In case you want to include multiple slideviews in one page in a Rmd or flexdashboard we highly recommend using package widgetframe. Also, make sure to use different image names and/or labels for each of the RasterLayers/Bricks/Stacks. Otherwise things will likely not work properly.

This is a modified implementation of http://bl.ocks.org/rfriberg/8327361

Usage

# S4 method for RasterStackBrick,RasterStackBrick
slideView(
  img1,
  img2,
  label1 = deparse(substitute(img1, env = parent.frame())),
  label2 = deparse(substitute(img2, env = parent.frame())),
  r = 3,
  g = 2,
  b = 1,
  na.color = "#BEBEBE",
  maxpixels = 1e+07,
  ...
)

# S4 method for RasterLayer,RasterLayer
slideView(
  img1,
  img2,
  label1 = deparse(substitute(img1, env = parent.frame())),
  label2 = deparse(substitute(img2, env = parent.frame())),
  legend = TRUE,
  col.regions = viridisLite::inferno(256),
  na.color = "#BEBEBE",
  maxpixels = 1e+07
)

# S4 method for RasterStackBrick,RasterLayer
slideView(
  img1,
  img2,
  label1 = deparse(substitute(img1, env = parent.frame())),
  label2 = deparse(substitute(img2, env = parent.frame())),
  legend = TRUE,
  r = 3,
  g = 2,
  b = 1,
  col.regions = viridisLite::inferno(256),
  na.color = "#BEBEBE",
  maxpixels = 1e+07,
  ...
)

# S4 method for RasterLayer,RasterStackBrick
slideView(
  img1,
  img2,
  label1 = deparse(substitute(img1, env = parent.frame())),
  label2 = deparse(substitute(img2, env = parent.frame())),
  legend = TRUE,
  r = 3,
  g = 2,
  b = 1,
  col.regions = viridisLite::inferno(256),
  na.color = "#BEBEBE",
  maxpixels = 1e+07,
  ...
)

# S4 method for character,character
slideView(
  img1,
  img2,
  label1 = deparse(substitute(img1, env = parent.frame())),
  label2 = deparse(substitute(img2, env = parent.frame()))
)

# S4 method for ANY
slideview(...)

Arguments

img1

a RasterStack/Brick, RasterLayer or path to a .png file

img2

a RasterStack/Brick, RasterLayer or path to a .png file

label1

slider label for img1 (defaults to object name)

label2

slider label for img2 (defaults to object name)

r

integer. Index of the Red channel, between 1 and nlayers(x)

g

integer. Index of the Green channel, between 1 and nlayers(x)

b

integer. Index of the Blue channel, between 1 and nlayers(x)

na.color

the color to be used for NA pixels

maxpixels

integer > 0. Maximum number of cells to use for the plot. If maxpixels < ncell(x), sampleRegular is used before plotting.

...

additional arguments passed on to repective functions.

legend

whether to plot legends for the two images (ignored for RatserStacks/*Bricks).

col.regions

color (palette).See levelplot for details.

color

the color palette to be used for visualising RasterLayers

Details

Compare two images trough interactive swiping overlay

For slideView there are a few keyboard shortcuts defined:

• space - toggle antialiasing

• esc - zoom to layer extent

• enter - set zoom to 1

• ctrl - increase panning speed by 10

Methods (by class)

• img1 = RasterLayer,img2 = RasterLayer: for RasterLayers

• img1 = RasterStackBrick,img2 = RasterLayer: for RasterStackBrick, RasterLayer

• img1 = RasterLayer,img2 = RasterStackBrick: for RasterLayer, RasterStackBrick

• img1 = character,img2 = character: for png files

• ANY: alias for ease of typing

Author

Tim Appelhans

Stephan Woellauer

Examples

if (interactive()) {
### example taken from
### http://www.news.com.au/technology/environment/nasa-images-reveal-
### aral-sea-is-shrinking-before-our-eyes/story-e6frflp0-1227074133835

library(jpeg)
library(raster)

web_img2000 <- "http://cdn.newsapi.com.au/image/v1/68565a36c0fccb1bc43c09d96e8fb029"

jpg2000 <- readJPEG(readBin(web_img2000, "raw", 1e6))

# Convert imagedata to raster
rst_blue2000 <- raster(jpg2000[, , 1])
rst_green2000 <- raster(jpg2000[, , 2])
rst_red2000 <- raster(jpg2000[, , 3])

img2000 <- brick(rst_red2000, rst_green2000, rst_blue2000)

web_img2013 <- "http://cdn.newsapi.com.au/image/v1/5707499d769db4b8ec76e8df61933f2a"

jpg2013 <- readJPEG(readBin(web_img2013, "raw", 1e6))

# Convert imagedata to raster
rst_blue2013 <- raster(jpg2013[, , 1])
rst_green2013 <- raster(jpg2013[, , 2])
rst_red2013 <- raster(jpg2013[, , 3])

img2013 <- brick(rst_red2013, rst_green2013, rst_blue2013)

slideView(img2000, img2013, label1 = "before", label2 = "after")
}