Using python PIL to turn a RGB image into a pure black and white image

Question

I m using the Python Imaging Library for some very simple image manipulation  however I m having trouble converting a greyscale image to a monochrome  black and white  image  If I save after changing the image to greyscale  convert  L    then the image renders as you would expect  However  if I convert the image to a monochrome  single-band image it just gives me noise as you can see in the images below  Is there a simple way to take a colour png image to a pure black and white image using PIL   python  from PIL import Image  import ImageEnhance import ImageFilter from scipy misc import imsave image file   Image open  quot convert image png quot     open colour image image file  image file convert  L     convert image to monochrome - this works image file  image file convert  1     convert image to black and white imsave  result col png   image file

User · Answer

A simple way to do it using python     Python import numpy as np import imageio  image   imageio imread r  image-path    as gray True     getting the threshold value thresholdValue   np mean image     getting the dimensions of the image xDim  yDim   image shape    turn the image into a black and white image for i in range xDim       for j in range yDim           if  image i  j   gt  thresholdValue               image i  j    255         else              image i  j    0

User · Answer

A PIL only solution for creating a bi-level  black and white  image with a custom threshold   from PIL import Image img   Image open  mB96s png   thresh   200 fn   lambda x   255 if x  gt  thresh else 0 r   img convert  L   point fn  mode  1   r save  foo png     With just  r   img convert  1   r save  foo png     you get a dithered image   From left to right the input image  the black and white conversion result and the dithered result       You can click on the images to view the unscaled versions

User · Answer

As Martin Thoma has said  you need to normally apply thresholding  But you can do this using simple vectorization which will run much faster than the for loop that is used in that answer   The code below converts the pixels of an image into 0  black  and 1  white     from PIL import Image import numpy as np import matplotlib pyplot as plt   Pixels higher than this will be 1  Otherwise 0  THRESHOLD VALUE   200   Load image and convert to greyscale img   Image open  photo png   img   img convert  L    imgData   np asarray img  thresholdedData    imgData  gt  THRESHOLD VALUE    1 0  plt imshow thresholdedData  plt show

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Another option  which is useful e g  for scientific purposes when you need to work with segmentation masks  is simply apply a threshold      usr bin env python   - - coding  utf-8 - -     Binarize  make it black and white  an image with Python      from PIL import Image from scipy misc import imsave import numpy   def binarize image img path  target path  threshold          Binarize an image         image file   Image open img path      image   image file convert  L      convert image to monochrome     image   numpy array image      image   binarize array image  threshold      imsave target path  image    def binarize array numpy array  threshold 200          Binarize a numpy array         for i in range len numpy array            for j in range len numpy array 0                 if numpy array i  j   gt  threshold                  numpy array i  j    255             else                  numpy array i  j    0     return numpy array   def get parser           Get parser object for script xy py         from argparse import ArgumentParser  ArgumentDefaultsHelpFormatter     parser   ArgumentParser description   doc                                formatter class ArgumentDefaultsHelpFormatter      parser add argument  -i    --input                           dest  input                           help  read this file                           metavar  FILE                           required True      parser add argument  -o    --output                           dest  output                           help  write binarized file hre                           metavar  FILE                           required True      parser add argument  --threshold                           dest  threshold                           default 200                          type int                          help  Threshold when to show white       return parser   if   name         main         args   get parser   parse args       binarize image args input  args output  args threshold    It looks like this for   binarize py -i convert image png -o result bin png --threshold 200

User · Answer

from PIL import Image  image file   Image open  convert image png     open colour image image file   image file convert  1     convert image to black and white image file save  result png     yields

[python] Using python PIL to turn a RGB image into a pure black and white image

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