How can I convert a color image to grayscale in MATLAB?

Question

I am trying to implement an algorithm in computer vision and I want to try it on a set of pictures. The pictures are all in color, but I don't want to deal with that. I want to convert them to grayscale which is enough for testing the algorithm.

How can I convert a color image to grayscale?

I'm reading it with:

x = imread('bla.jpg');

Is there any argument I can add to imread to read it as grayscale? Is there any way I change x to grayscale after reading it?

score 25 · Accepted Answer · edited Nov 28 '16 at 10:00

25

Use rgb2gray to strip hue and saturation (ie, convert to grayscale). Documentation

edited Nov 28 '16 at 10:00

Seanny123

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answered Nov 22 '09 at 19:17

Donnie

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They really need to stop moving the documentation. :) – Donnie Apr 21 '13 at 02:12

score 8 · Answer 2 · edited Dec 27 '09 at 13:03

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x = imread('bla.jpg');
k = rgb2gray(x);
figure(1),imshow(k);

edited Dec 27 '09 at 13:03

Nathan Fellman

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answered Dec 27 '09 at 12:05

s.lakshmi

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>> k = rgb2gray(im); Undefined function 'rgb2gray' for input arguments of type 'uint8'. – ntg Dec 11 '13 at 19:08

score 2 · Answer 3 · answered Nov 11 '12 at 19:54

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you can using this code:

im=imread('your image');
k=rgb2gray(im);
imshow(k);

using to matlab

answered Nov 11 '12 at 19:54

Dian Permata

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score 2 · Answer 4 · edited Jun 29 '11 at 08:41

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I found this link: http://blogs.mathworks.com/steve/2007/07/20/imoverlay-and-imagesc/ it works.

it says:

im=imread('your image');
m=mat2gray(im);
in=gray2ind(m,256);
rgb=ind2rgb(in,hot(256));
imshow(rgb);

edited Jun 29 '11 at 08:41

Nathan Fellman

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answered Jun 29 '11 at 07:21

Ema

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score 1 · Answer 5 · edited Oct 14 '15 at 12:58

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I=imread('yourimage.jpg');
p=rgb2gray(I)

edited Oct 14 '15 at 12:58

Wai Ha Lee

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answered Oct 14 '15 at 12:45

SPIRO TECH GURU

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I know that the answer is simple, but code-only answers are discouraged here. Please add a little context, explain what `rgb2gray` does and maybe link to the documentation. – horchler Oct 14 '15 at 17:56

Alimpk · Answer 6 · 2017-06-14T21:41:22.123

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Use the imread() and rgb2gray() functions to get a gray scale image.

Example:

I = imread('input.jpg');
J = rgb2gray(I);
figure, imshow(I), figure, imshow(J);

If you have a color-map image, you must do like below:

[X,map] = imread('input.tif');
gm = rgb2gray(map);
imshow(X,gm);

The rgb2gray algorithm for your own implementation is :

f(R,G,B) = (0.2989 * R) + (0.5870 * G) + (0.1140 * B)

edited Jun 14 '17 at 21:41

answered Jun 14 '17 at 14:34

Alimpk

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Syed Ali Shahzil · Answer 7 · 2021-04-12T17:01:46.060

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Color Image

Gray Scale image

  bg = imread('C:\Users\Ali Sahzil\Desktop\Media.png');  // Add your image 
  redChannel = bg(:, :, 1);
  greenChannel = bg(:, :, 2);
  blueChannel = bg(:, :, 3);
  grayImage = .299*double(redChannel) + .587*double(greenChannel) 
  +.114*double(blueChannel);
  imshow(grayImage);

edited Apr 12 '21 at 17:01

answered Apr 12 '21 at 16:44

Syed Ali Shahzil

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Is this a better solution than using the built-in `rgb2gray`? – Nathan Fellman Apr 25 '21 at 12:01
Yeah, it is completely fine to use the build-in function but doing thing manual gives you a better understanding of how a grayscale image is generated. – Syed Ali Shahzil Apr 26 '21 at 13:32

How can I convert a color image to grayscale in MATLAB?

7 Answers7

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