How to do in R: load an image file, print text on image, save modified image

Question

... Ideally, with a PNG image file, if not JPEG. I can load a flie with

library(png)
img = readPNG("chart.png")

but am stuck there. The goal is to type "Hello world" on the image and save it.

Thank you.

This blog post might be of interest http://www.r-bloggers.com/adding-watermarks-to-plots/ — jdharrison, May 22 '14 at 12:45
use `image` or other tool to plot the image; use `text` or other tool to write stuff onto the plot; save the plot. — Carl Witthoft, May 22 '14 at 13:35
http://stackoverflow.com/questions/12918367/in-r-how-to-plot-with-a-png-as-background — Dimitri Shvorob, May 22 '14 at 14:19

score 20 · Answer 1 · answered May 22 '14 at 20:25

I think this should work just fine

library(png)

#read file
img<-readPNG("33.png")

#get size
h<-dim(img)[1]
w<-dim(img)[2]

#open new file for output
png("out.png", width=w, height=h)
par(mar=c(0,0,0,0), xpd=NA, mgp=c(0,0,0), oma=c(0,0,0,0), ann=F)
plot.new()
plot.window(0:1, 0:1)

#fill plot with image
usr<-par("usr")    
rasterImage(img, usr[1], usr[3], usr[2], usr[4])

#add text
text(.5,.5, "hello", cex=5, col=rgb(.2,.2,.2,.7))

#close image
dev.off()

How to do in R: load an image file, print text on image, save modified image

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