Applying a coloured overlay to an image in either PIL or Imagemagik

Question

I am a complete novice to image processing, and I am guessing this is quite easy to do, but I just don\'t know the terminology.

Basically, I have a black and white im

Answer 1

I ended up finding an answer to this using PIL, basically creating a new image with a block colour, and then compositing the original image, with this new image, using a mask that defines a transparent alpha layer. Code below (adapted to convert every image in a folder called data, outputting into a folder called output):

from PIL import Image
import os

dataFiles = os.listdir('data/')

for filename in dataFiles:

    #strip off the file extension
    name = os.path.splitext(filename)[0]

    bw = Image.open('data/%s' %(filename,))

    #create the coloured overlays
    red = Image.new('RGB',bw.size,(255,0,0))
    green = Image.new('RGB',bw.size,(0,255,0))
    blue = Image.new('RGB',bw.size,(0,0,255))
    yellow = Image.new('RGB',bw.size,(255,255,0))

    #create a mask using RGBA to define an alpha channel to make the overlay transparent
    mask = Image.new('RGBA',bw.size,(0,0,0,123))

    Image.composite(bw,red,mask).convert('RGB').save('output/%sr.bmp' % (name,))
    Image.composite(bw,green,mask).convert('RGB').save('output/%sg.bmp' % (name,))
    Image.composite(bw,blue,mask).convert('RGB').save('output/%sb.bmp' % (name,))
    Image.composite(bw,yellow,mask).convert('RGB').save('output/%sy.bmp' % (name,))

Can't post the output images unfortunately due to lack of rep.