RGB Image to Grayscale Image without using rgb2gray function

A gray-scale image is composed of different shades of grey color.
A true color image can be converted to a gray scale image by preserving the luminance(brightness) of the image.

Here the RGB image is a combination of RED, BLUE AND GREEN colors.
The RGB image is 3 dimensional. In an image ,

at a particular position say  ( i,j)
Image(i,j,1) gives the value of RED pixel.
Image(i,j,2) gives the value of BLUE pixel.
Image(i,j,3) gives the value of GREEN pixel.
The combination of these primary colors are normalized with R+G+B=1;
This gives the neutral white color.

The grayscale image is obtained from the RGB image by combining 30% of RED , 60% of GREEN and 11% of BLUE.
This gives the brightness information of the image. The resulting image will be two dimensional. The value 0 represents black and the value 255 represents white. The range will be between black and white values.


MATLAB CODE:

Im=imread('peppers.png');

figure,imshow(Im);
title('Original Image');

%0.2989 * R + 0.5870 * G + 0.1140 * B
GIm=uint8(zeros(size(Im,1),size(Im,2)));
for i=1:size(Im,1)
      for j=1:size(Im,2)
          GIm(i,j)=0.2989*Im(i,j,1)+0.5870*Im(i,j,2)+0.1140*Im(i,j,3);
      end
end

%Without using for loop:

%GIm=0.2989*Im(:,:,1)+0.5870*Im(:,:,2)+0.1140*Im(:,:,3);

figure,imshow(GIm);
title('Grayscale Image');

Check out : Partially colored gray scale image - MATLAB CODE