Add text on images using R

A short description of the post.

Miriam Lerma true
2024-05-02

Intro

This post is to edit images in R.

Using R assures that your image would not be compress as happens when you open it with some other programs.

The blog consist of two parts:
1. Add letter to a picture and export
2. Merge two pictures into one and export

1. Add letter to a picture and export

Packages

Use the package magick to process images in R.

For more information: https://docs.ropensci.org/magick/articles/intro.html#read-and-write

To install the package

install.packages("magick")

To call the package

library(magick)

Data

Select your directory. In the example, as My_directory.

library(here)
My_directory<-here()

Check if you gave the correct path by using the function list.files.
It should show the images you want to use.

list.files(My_directory)

Read images using the function image_read.

Fig1_original<- image_read(paste0(My_directory,"\\MABO.JPG"))

The function image_draw will show the picture in the Viewer.
Moreover, it gives information on the width and height of the picture.

Fig1_draw<-image_draw(Fig1_original)
Fig1_draw

Add text

To add text use the function image_annotate

To add the text in the right bottom use the information from the dimensions above to define the xaxis and yaxis.

Fig1_text<-image_annotate(Fig1_draw, "(a)",  location = "+1199+999", font = 'Arial', size = 100, color='white')

To add the text in the left top part you can use define the xaxis and yaxis as 100.

Fig1_text<-image_annotate(Fig1_draw, "(a)",  location = "+50+50", font = 'Arial', size = 100, color='white')

Export

Use the function image_write to export.

image_write(Fig1_text, path = paste0(My_directory,"/Fig1_tl.png"), format = "png")

2. Merge two pictures into one and export

Follow the same steps as above, but with a second picture.

Fig2_original<- image_read(paste0(My_directory,"\\RFBO.JPG"))
Fig2_draw<-image_draw(Fig2_original)
Fig2_text<-image_annotate(Fig2_draw, "(b)",  location = "+50+50", font = 'Arial', size = 100, color='white')
image_write(Fig2_text, path = paste0(My_directory,"/Fig2_lt.png"), format = "png")

Add border

Use the function image_border to add some space between the pictures.

Fig1_border<-image_border(image_background(Fig1_text, "transparent"), "white", "40x10")
Fig1_border

Fig2_border<-image_border(image_background(Fig2_text, "transparent"), "white", "40x10")
Fig2_border

Combine

Use the function image_append to have both pictures side by side.

image_append(c(Fig1_border,Fig2_border))

Export

Use the function image_write to export the picture.

image_write(image_append(c(Fig1_border,Fig2_border)), path = paste0(My_directory,"/Fig1_append.png"), format = "png")

End of document