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# how to convert gray scale image into rgb image?

Asked by ug on 1 Apr 2013

my project is on iridiology...and it requires to convert the gray scale image to an rgb image to find the basic color of the iris. am in need of the code to convert the gray scale image to rgb image.

## Products

Answer by Image Analyst on 2 Apr 2013

You ask: "i hav an image of the iris with all extra features like eye lashes n all..i hav to extract only the iris frm tis image. first i select the two circles of the iris..the resultant image is that the coloured part of the iris is converted to gray scale n the rest is blacked out... but i want to get the original colour....is there ne other method to get the colour of the iris?"

Here's how to do it.

```% Make a mask from your circle using poly2mask
% xCircle, yCircle are the coordinates of your circle perimeter.
% Now mask the image so that only the original RGB part
% inside the circle remains, and outside the circle is set to black.
```

Answer by Ahmed A. Selman on 1 Apr 2013

Use colormap types, since you are interested with a colored region of interest, I think any colormap format suffices. Example:

```   close all
clear
clc % just to clear things up
R=rgb2gray(I); % It is gray now
y=colormap(hot(110));
imwrite(R,y,'rgb.jpg','jpg'); % Re-change it to colored one
imshow('rgb.jpg');```

Image Analyst on 2 Apr 2013

Please explain why you think it is even possible to recover "the basic color of the iris". Did you snap the original iris image with a color camera or a monochrome camera?

ug on 2 Apr 2013

here is the procedure, i hav an image of the iris with all extra features like eye lashes n all..i hav to extract only the iris frm tis image. first i select the two circles of the iris..the resultant image is that the coloured part of the iris is converted to gray scale n the rest is blacked out... but i want to get the original colour....is there ne other method to get the colour of the iris?

Image Analyst on 2 Apr 2013

Of course. Wish you'd explained that initially. See my new answer.

Answer by Mahdi on 1 Apr 2013

Gabriel made a script for that. You can find it here.

## 1 Comment

ug on 2 Apr 2013

this did nt work too

Answer by Image Analyst on 1 Apr 2013

ug, if your starting image is monochrome, then you cannot determine the original color. You cannot. Not if all you have is the grayscale image. Period.

You can convert a grayscale image into an RGB image using cat():

```rgbImage = cat(3, grayImage, grayImage, grayImage);
```

of course it will look all grayscale even though it is a "true color" RGB image - it's just that all the "colors" are gray. You can apply a pseudocolor lookup table to the gray values, where each gray value gets mapped into some color, to get a multi-colored image, like this:

```rgbImage = ind2rgb(grayImage, jet(256));
```

however the colors are NOT the original colors of the iris as if you had snapped it with a color camera.

ug on 2 Apr 2013

am getting an error in the ind2rgb function... sayin the dimensions don match

Image Analyst on 2 Apr 2013

Like I said before see my new answer ( http://www.mathworks.com/matlabcentral/answers/69368#answer_80694). ind2rgb() doesn't apply anymore. You will not be using ind2rgb. Again, see my new answer above.

Answer by ug on 1 Apr 2013
``` @Ahmed A. Selman
Am getting the following errors:
??? Error: File: C:\MATLAB7\toolbox\images\images\private\checkinput.m Line: 38 Column: 1
Incomplete or misformed expression or statement.```

Error in ==> images\private\checkstrs at 26 checkinput(in, 'char', 'row', function_name, variable_name, argument_position);

Error in ==> imlincomb>ParseInputs at 95 output_class = checkstrs(varargin{end}, valid_strings, mfilename, ...

Error in ==> imlincomb at 83 [images, scalars, output_class] = ParseInputs(varargin{:});

Error in ==> rgb2gray at 58 I = imlincomb(coef(1),X(:,1),coef(2),X(:,2),coef(3),X(:,3), ...

Error in ==> trial at 5 R=rgb2gray(I); % It is gray now

Ahmed A. Selman on 2 Apr 2013

True, Analyst, I do agree with the idea that when color is lost it cannot be retained correctly. Thus any color map can do the job mentioned in the question with the same quality, give or take; they all will NOT be correct, but ANY could specifically isolate iris from the rest, at least better than a grayscale image. In fact I do wonder what does (determine the basic color of the iris from gray images) means, I keep reading amazing stuff here. Correctly colored iris image from gray image is, without doubt, not possible unless a true image was used to specify the colormap .. and if true images do exist then why convert them to gray and ask how to retain the color?..

Anyway, industrially colored images do look like garbage, even when using highly sophisticated image software (truth has only one face..) but does it matter if it was using hot or jet or any other map? If there is a difference please specify what kind is better -- new info are useful and appreciated, always. If not, however, then old or new colormaps will be all as crappy as the same, right? :)

Image Analyst on 2 Apr 2013

We're in agreement here. If all you want to do is to colorize it, you can pick whatever colormap you feel looks best or suits your needs - it's totally subjective.

Ahmed A. Selman on 2 Apr 2013

My exact point. Thank you.

Answer by G.Liz on 31 Jul 2013

Does anyone know how to segment the sclera of the eye ?

## 1 Comment

Walter Roberson on 31 Jul 2013

Please start a new Question for that.