Display Image Data in R
How to display image data with R.
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This tutorial shows how to display and explore image data. If you would like instead a logo or static image, use layout.Image
as explained here.
Display RGB Image Data with Image Trace
Note that Image
trace only accepts multichannel images. For single images, use Heatmap
. Image
trace is different from the layout.Image
class, which can be used for adding background images or logos to figures.
library(plotly)
library(EBImage)
img_rgb = list(list(c(255, 0, 0),c(0, 255, 0),c(0, 0, 255)),
list(c(0,255, 0),c(0, 0, 255),c(255, 0, 0)))
fig <- plot_ly(type="image", z=img_rgb)
fig
Read image arrays from image files
In order to create a numerical array to be passed to Image
trace, you can use a third-party library like EBImage to open an image from a URL.
library(plotly)
library(EBImage)
img = readImage('https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Crab_Nebula.jpg/240px-Crab_Nebula.jpg')
fig <- plot_ly(type="image", z=img*255)
fig
Define the data range covered by the color range with zmin and zmax
The data range and color range are mapped together using the parameters zmin
and zmax
, which correspond respectively to the data values mapped to black [0, 0, 0]
and white [255, 255, 255]
.
The default value of zmin
and zmax depends on the colormodal
value. In this example colormodel is "rgb"
(by default), so the default value of zmin is [0, 0, 0]
and zmax is [250, 250, 250]
.
library(plotly)
library(EBImage)
img = readImage('https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Crab_Nebula.jpg/240px-Crab_Nebula.jpg')
# Stretch the contrast of the red channel only, resulting in a more red image
fig <- plot_ly(type="image", z=img*250,
zmin=c(10, 0, 0), zmax=c(200, 250, 250))
fig