How to Convert an Rgb Image into Grayscale in Python

How can I convert an RGB image into grayscale in Python?

How about doing it with Pillow:

from PIL import Image
img = Image.open('image.png').convert('L')
img.save('greyscale.png')

---

If an alpha (transparency) channel is present in the input image and should be preserved, use mode LA:

img = Image.open('image.png').convert('LA')

---

Using matplotlib and the formula

Y' = 0.2989 R + 0.5870 G + 0.1140 B 

you could do:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.image as mpimg

def rgb2gray(rgb):
    return np.dot(rgb[...,:3], [0.2989, 0.5870, 0.1140])

img = mpimg.imread('image.png')     
gray = rgb2gray(img)    
plt.imshow(gray, cmap=plt.get_cmap('gray'), vmin=0, vmax=1)
plt.show()

Converting RGB to grayscale python

I think it is because of skimage. why dont you use just opencv.

import numpy
import glob
import cv2
import csv
import math
import os
import string
from skimage.color import rgb2gray
from PIL import Image

mylist = [f for f in glob.glob("*.jpg")]

for imagefile in mylist:
    img_color = cv2.imread(imagefile)
    image = cv2.resize(img_color,(100,100),interpolation = cv2.INTER_AREA)
    img_gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    #img_gray = rgb2gray(image)
    img_gray.flatten()
    cv2.imwrite("gray"+imagefile,img_gray)

Convert Color Image to Grayscale in Python without OpenCV

You could write it, based on the conversion formula "Standard" RGB to Grayscale Conversion:

import numpy as np

def rgb2gray(rgb):

    r, g, b = rgb[:,:,0], rgb[:,:,1], rgb[:,:,2]
    gray = 0.2989 * r + 0.5870 * g + 0.1140 * b

    return gray

How to convert RGB images to grayscale, expand dimensions of that grayscale image to use in InceptionV3?

In ImageDataGenerator, you can pass a preprocessing function. Use the functions tf.image.rgb_to_grayscale and tf.image.grayscale_to_rgb to do the transformation:

def to_grayscale_then_rgb(image):
    image = tf.image.rgb_to_grayscale(image)
    image = tf.image.grayscale_to_rgb(image)
    return image

tf.keras.preprocessing.image.ImageDataGenerator(
    rescale=1/255,
    preprocessing_function=to_grayscale_then_rgb
)

RGb to gray conversion in CV2

The default option for cmap in plt.imshow is viridis. Use plt.imshow(gray, cmap='gray') for grayscale images. If you save the image using cv2.imwrite you can see the image has been converted to grayscale.

how to convert rgb image To grayscale in python

First of all, it seems like you are working with an array of 267 of 100x100 RGB images here. I am assuming you are using a NumPy array. In order to convert the images to grayscale you can use the method proposed in this answer:

def rgb2gray(rgb):
    return np.dot(rgb[...,:3], [0.2989, 0.5870, 0.1140])

x_train_gray = rgb2gray(x_train)

Note that this works for all images in one pass and the resulting shape should be (267, 100, 100). However, np.imshow only works for one image at a time so to plot an image in grayscale you can do the following:

plt.imshow(x_train_gray[0], cmap=plt.get_cmap('gray'), vmin=0, vmax=1)
plt.show()

---

Related Topics