zfactor_imgdata

from PIL import Image
from numpy import array

im = Image.open('spectrum.png') # your image here
width = im.width
height = im.height
colorchannels = 3

rgb_im = im.convert('RGB')

# data is 1-d list of [r,g,b] value sets
data = list(rgb_im.getdata())

# reshape data into height x width x colorchannels
samples = array(data).reshape(height,width,colorchannels)

# samples[0] is the first row, left to right
# samples[height-1] is the last row
# samples[0][0] is the first pixel [r,g,b] upper left corner
# samples[height-1][width-1] is the last pixel lower right corner

#leftbound = width/2
#topbound = height/2
#boundwidth = 100
#boundheight = 100
# to take [r,g,b] measurements from an area
# of known height, width, left, and top boundaries;
# set the variables and iterate
#   from
#     samples[topbound][leftbound]
#   to
#     samples[topbound+boundheight][samples[leftbound+boundwidth]
# using something like this:

#for y in range(boundheight):
#    for x in range(boundwidth):
#        # do something with
#        #   samples[topbound+y][leftbound+x]
#        # to go left-right top-bottom in the boundary