MATLAB Answers

## RGB TO GRAY ERROR

Asked by TULIKA

### TULIKA (view profile)

on 22 Aug 2014
Latest activity Commented on by Youssef Khmou

### Youssef Khmou (view profile)

on 25 Aug 2014
Accepted Answer by Youssef Khmou

### Youssef Khmou (view profile)

```x= 1:150;y=1:150;
[p,q]=freqspace(150);
[X,Y]=meshgrid(p,q);
R=(X.^2 + Y.^2);
Lambda=633*10^-9;
dis=10*10^-3;
F = (exp(i.*pi.*R))./(Lambda.*dis);
mesh(imag(F));
there is an ouput which i have to convert into gray image.
HOW to convert into gray image...i have an error
Map myst be m*3 matrix?
how will i do this?
```

TULIKA

### TULIKA (view profile)

on 23 Aug 2014

i didn't code before mesh(imag(F)).i did after this line..that is

```F1=rgb2gray(F)
so there is an error .....
Map must be m*3 matrix?
how to apply before mesh(imag(F))
i'm new to matlab.i didn't konw so much coding...
```
Image Analyst

### Image Analyst (view profile)

on 23 Aug 2014

F is not a grayscale image! Is this not solved yet? Did you see my solution?

TULIKA

### TULIKA (view profile)

on 23 Aug 2014

yeah I did..if i send u the complete program will u check the whole program??plzzz...

## 2 Answers

### Youssef Khmou (view profile)

Answer by Youssef Khmou

### Youssef Khmou (view profile)

on 23 Aug 2014
Accepted answer

This is numeric problem, no need for images processing tools, in fact you are computing a type of two dimensional exponential function, you have many ways to visualize your function :

`    figure; surface(abs(F))`

TULIKA

### TULIKA (view profile)

on 23 Aug 2014

the output of the program is an coloured output.....when i convert this output to grey colour with rgb2gray there is an error.... i want to convert the output into grey scale..... plzz help

Youssef Khmou

### Youssef Khmou (view profile)

on 25 Aug 2014

try the following command :

` colormap gray`

### Image Analyst (view profile)

Answer by Image Analyst

### Image Analyst (view profile)

on 23 Aug 2014
Edited by Image Analyst

### Image Analyst (view profile)

on 23 Aug 2014

TULIKA, I know you already accepted an answer, so maybe you don't need my answer anymore, but I had this already to post and then I got to watching a movie and didn't post it until now. Well, for whatever it's worth, here it is. If it helps in any way, maybe you can vote for it:

```clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 13;
```
```x= 1:150;y=1:150;
[p,q]=freqspace(150);
[X,Y]=meshgrid(p,q);
R=(X.^2 + Y.^2);
Lambda=633*10^-9;
dis=10*10^-3;
F = (exp(i.*pi.*R))./(Lambda.*dis);
```
```% Convert into a gray scale image and display it as a mesh.
subplot(1, 3, 1);
grayImage = imag(F); % Gray scale image = imaginary part.
mesh(grayImage);
axis square
title('Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
```
```% Display grayscale image.
subplot(1, 3, 2);
imshow(grayImage, []);
title('Grayscale Image', 'FontSize', fontSize);
colormap(gray(256));
colorbar;
```
```% Convert into a color image, just for fun
rgbImage = ind2rgb(uint8(255*mat2gray(grayImage)), jet(256));
subplot(1, 3, 3);
imshow(rgbImage, []);
title('RGB Image', 'FontSize', fontSize);
```

TULIKA

### TULIKA (view profile)

on 23 Aug 2014

this is the image

Image Analyst

### Image Analyst (view profile)

on 23 Aug 2014

You're basically convolving that image with itself, which is an autocorrelation, so you should see a spike at the middle, followed by a rapid fall off. Of course the second half of your code has nothing to do with the first half of your code. What are you attempting to achieve? Perhaps you should start a new discussion if we're going to be talking about new topics of convolution or autocorrelation or spatial filtering, as you've already marked this one as Accepted and many people may not bother to look anymore.

TULIKA

### TULIKA (view profile)

on 23 Aug 2014

Sir,i'm new to matlab,even i don't know so much coding and didn't understand what you have said.I have to code the convolution of the two images i.e the output of the program and the image (i have sent)one in space domain and another frequency domain,yeah i have unintentionally clicked that option and it accepted the answer... there is no error in the program but output figure is unexpected and the two outputs in space domain convolution and in frequency domain convolution are to be same...

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