Converting RGB to grayscale python

Question

I have been converting rgb images to grayscale images, below is the code

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 = rgb2gray(image)
    img_gray.flatten()

Im not getting the new image saved into my current folder. Can anyone help me regarding this.

You should write the image using `cv2.imwrite("new_img.jpg", img_gray)` — Sociopath, Feb 04 '20 at 05:02
Yeah the images are present in mylist, I read all the images in the current directory and printed the list out. — Vamsi Shankar, Feb 04 '20 at 05:10
You don't appear to be writing the image to disk, so how were you hoping it would work? Also, if you want a greyscale image, you can just open it in greyscale in the first place by changing the second parameter to `cv2.imread()`. — Mark Setchell, Feb 04 '20 at 08:01

score 2 · Accepted Answer · answered Feb 04 '20 at 05:55

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)

score 1 · Answer 2 · edited Aug 12 '23 at 16:24

1

You could also do this in one step if you want by adding an additional parameter to imread like this:

import cv2
imagefile = "path/to/file/filename.jpg"
gray = cv2.imread(imagefile, cv2.IMREAD_GRAYSCALE)
cv2.imshow('gray', gray)
cv2.waitKey()

edited Aug 12 '23 at 16:24

Nav

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answered Feb 04 '20 at 10:05

kalzso

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This is the best answer – Nav Aug 12 '23 at 16:24

Atinderpal Singh · Answer 3 · 2020-02-04T16:06:21.177

Basically you need to add code for saving image file:

import numpy
import glob
import cv2
import csv
import math
import os
import string
from skimage.color import rgb2gray
from skimage.io import imsave    # skimage method for saving image
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 = rgb2gray(image)
    img_gray.flatten()
    imsave("gray"+imagefile, img_gray)  # save the image

Or using opencv

img_gray = img_gray*255
cv2.imwrite("gray"+imagefile, img_gray.astype("uint8"))

But if you want to implement this entirely in skimage

import glob
from skimage.io import imread, imsave
from skimage.color import rgb2gray
from skimage.transform import resize

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

for imagefile in mylist:
    img_color = imread(imagefile)
    image = resize(img_color, (100, 100))
    img_gray = rgb2gray(image)
    img_gray.flatten()
    imsave("gray" + imagefile, img_gray)

I get this error when I implement entirely in skimage NameError: name 'im_path' is not defined — Vamsi Shankar, Feb 04 '20 at 12:52

Converting RGB to grayscale python

3 Answers3