intensity value of the pixel located

I have this question :

1-Read an image.

2-Show that image.

3-Write the image to the disk by new name.

4-Show additional info about image.

5-How to get the size of that image.

6-What is the intensity value of the pixel located at position(4,7)?

*I solved the previous five questions, but how can I solve the sixth question

figure

image=imread('Picture2.jpg')

imshow(image)

gray = rgb2gray(image)

imwrite(image,'House.jpg');

information = imfinfo('House.jpg')

information = information.FileSize

Answer 1

[Aditya Verma]

Your image is stored as a matrix in MATLAB. So, for getting the pixel intensity value you need to read the image:

image_mat = rgb2gray(imread('image.jpg'));  % image_mat is simply a matrix
disp(image_mat(4, 7));                      % Intensity at (4,7)

[Nour George]

I Wrote this :

figure

image=imread('Picture3.jpg')

imshow(image)

gray = rgb2gray(image)

imwrite(image,'House.jpg');

information = imfinfo('House.jpg')

information = information.FileSize

image_mat = rgb2gray(imread('Picture3.jpg')); % image_mat is simply a matrix

disp(im(4, 7));

But I get Error in the Last line " disp(im(4, 7)); "

Undefined function or variable 'im'.

How to solve it ?

[Aditya Verma]

Hi, it was a mistake in my code. I have corrected it. It should be:

disp(image_mat(4, 7));

[Aditya Verma]

By the way, if you're new to MATLAB or programming I would recommend you to take the free MATLAB Onramp course.

[Nour George]

The picture is colored, should I use rgb2gray()?

Answer 2

[Image Analyst]

Do not use image as the name of your variable. It is the name of a built-in function that you will destroy (temporarily).

The assignment did not say anything about converting to gray scale so why did you use rgb2gray()?

To get the value of a pixel, you can use impixel() or simply index it. A color image will have 3 intensities, one for each color channel.

[Image Analyst]

Well I'm sure you saw the code in the help for impixel:

RGB = imread('peppers.png');
% Determine the column c and row r indices of the pixels to extract.
c = [1 12 146 410];
r = [1 104 156 129];
% Return the data at the selected pixel locations.
pixels = impixel(RGB,c,r)

So I'm not sure what you're asking. Do need help in modifying that code like this?

theColor = impixel(image_mat, 7, 4);

Remember it's columns that come first, not rows. But that was so easy that I'm certain you would have been able to do that simple change of putting in 7 and 4 for the column and row and changing the name of the image variable, so I'm not really sure what you're asking.