How to get pixel data from an image using R

Question

Can anyone help me on how to get the RGB pixel data from an image in R?

I need this information to compare differences in bird plumage to aid in the understanding of

Answer 1

Take this tiny sample 3x3 pixel png image:

Then:

library('png')
download.file('http://i.stack.imgur.com/hakvE.png', 'sample.png')
img <- readPNG('sample.png')
pix.top.left <- img[1,1,]     # row 1, column 1
pix.bottom.left <- img[3,1,]  # row 3, column 1
pix.top.right <- img[1,3,]    # row 1, column 3

If you're reading a PNG image with alpha channel (as the sample image above), then each of the pix. variables is a vector with four entries, each entry corresponding to Red ,Green, Blue and Alpha values of the pixel.

> pix.top.left
[1] 1 0 0 1