display .mat file as an image ?

Hi All Matlab users,

I have an image in .mat file ... I have a problem with display it.

clear all;
I=load ('Data.mat');  % struct double 512x512
I=I.s.I;
I=double(I);
figure(1);
imshow(I);

Could someone help me please ?

I would appreciate for any help.

[Jan]

Beside the useless "clear all" (see http://www.mathworks.com/matlabcentral/answers/16484-good-programming-practice#answer_22301), what is the problem? Do you get an error message - if so, which one?

[Image Analyst]

Help with what? It's possible that could work if you had a variable called s, that was a structure and that had a member called I which was an array. Did you get an error or something? What does your save() function call look like - what you used when you saved "s" into Data.mat?

Answer 1

[Image Analyst]

Why don't you just do something like

% Load entire mat file contents into a structure.
% The structure has a member "I" that is a double 512x512 array.
storedStructure = load('Data.mat');

% Extract out the image from the structure into its own variable.
% Don't use I as the variable name - bad for several reasons.
imageArray = storedStructure.s.I;  % Or storedStructure.I depending on what members your structure has.

% Display the image in a brand new figure window.
figure(1);
% Display double image, scaled appropriately.
% No need to cast to uint8 - could even be bad
% if your double numbers don't span the 0-255 range nicely.
imshow(imageArray, []);

[SHRUTHI k]

can you plz explain the above code once again for me? what is I and s in it? so that i can use the code in my work.

[Image Analyst]

S is the structure that the original user saved when he called save() to create the mat file. And s has a field (member) called I. Those are not good descriptive names, as I pointed out to him, and as you now demonstrate, but those were his choices, not mine. I hate single letter variable names, except for loop indexes, because they lead to an alphabet soup of code that is hard to follow, understand, and maintain.

[Md. Mostafizur Rahman]

When I trying this code for display a mat file it shows

" Reference to non-existent field 's'. imageArray = storedStructure.s.I; "

What is the problem with my code?

[Image Analyst]

Your mat file does not have a variable in it called s. Look at storedStructure in the variable editor to see what fields it has. Or do one of these lines:

storedStructure = load(filename)  % Don't use a semicolon!!!

or

fieldnames(storedStructure)  % Don't use a semicolon!!!

[Sharmin Afrose]

Hello, I get this error:

Dot indexing is not supported for variables of this type.

Can you please help?

[Image Analyst]

Sure. First read this link:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

Then, in your new question (separate thread), attach your code and .mat file.

Answer 2

[agatte]

It is not good . I received en error : ??? Error using ==> uint8 Conversion to uint8 from struct is not possible.

I = load('Data.mat'); figure(1); imshow(uint8(I));

????

[Image Analyst]

Chandra's version did not accept the output of load() into a variable, like you did. In your code I would be a structure. Do what he did and leave off the I= so that "s" gets loaded into the function's workspace, then get the "I" member of "s" like you originally tried to do. But you never said what *your* code's error was, as Jan and I asked.

Answer 3

[Dark]

How do I display 512x512x5 .mat file as an image in Matlab ?

[Image Analyst]

You load the file, then you can extract the image from the structure and call imshow:

storedStructure = load(matFileName);
rgbImage = storedStructure.rgbImage;
imshow(rgbImage);

By the way Agata , have I answered your original question? If so please officially mark my answer as "Accepted".

[Dark]

My matFileName is volume_image.mat. I tried your steps but the 2nd line gives me an error - Reference to non-existent field 'rgbImage'.

[Image Analyst]

Dark, you're supposed to know the name of the variable you used, and replace rgbImage with the actual name. If you don't remember just put storedStructure on its own line and it will report its fields to the command window:

storedStructure  % Report fields to command window.

You will see one of the fields look like an image. Use the name of that one to replace rgbImage in my code.

[Dark]

Thanks for your quick reply. I followed your code and get an image. However the image that I get using imshow() is just black and white. I even tried using imshow(rgbImage, []). I basically have 5 dicom slices of a bone which I converted into .mat file. Then I followed your code. How do I view the 5 dicom images in Matlab ?

[Tain Neupane]

Hey Dark,

You can use imtool (X (:,:,n)) to display info slice by slice but I am not sure how to display whole image at once! I have an Image of size 512x512x125. I am having difficulties to display all at once and looking for help here. Thank you.

-Tain

[Image Analyst]

@Tain Neupane you can use imshow and impixelinfo

If you have any more questions, then start your own completely new thread, and attach your data and code to read it in with the paperclip icon after you read this:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

Answer 4

[Annie micheal]

How to convert 100 face images to .mat file of the form 20*20*100 where 20*20 is the face template and 100 is the number of images.

[Image Analyst]

Resize each image with imresize(). Then save into a cell array or a 3 or 4D matrix and call save() to save into a mat file on disk.

[Annie micheal]

I'm new to matlab. Pls send me a sample code for the above conversion

[Image Analyst]

Code samples are in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

Try this in the loop

resizedImage(:,:,k) = imresize(rgbImage, [20, 20]);

[Annie micheal]

Thanks a lot.. Its working.. But its not working for RGB image. My code is clc;clear all;close all; % Specify the folder where the files live. myFolder = 'C:/Users/DELL/Documents/MATLAB/face detection/NPD/NPDFaceDetector_Train/data/face'; % Check to make sure that folder actually exists. Warn user if it doesn't. if ~isdir(myFolder) errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder); uiwait(warndlg(errorMessage)); return; end % Get a list of all files in the folder with the desired file name pattern. filePattern = fullfile(myFolder, '*.jpg'); % Change to whatever pattern you need. theFiles = dir(filePattern); for k = 1 : length(theFiles) baseFileName = theFiles(k).name; fullFileName = fullfile(myFolder, baseFileName); fprintf(1, 'Now reading %s\n', fullFileName); imageArray = imread(fullFileName); for n = 1 : length(theFiles) FaceDB(:,:,n) = imresize(imageArray, [20 20]); end savefile='FaceDB.mat'; save(savefile,'FaceDB'); end

i get this error Now reading C:\Users\DELL\Documents\MATLAB\face detection\NPD\NPDFaceDetector_Train\data\face\1.jpg Subscripted assignment dimension mismatch.

Error in mat (line 19) FaceDB(:,:,n) = imresize(imageArray, [20 20]);

 how to fix this error?

[Image Analyst]

Did you define FaceDB in advance of your loop?

FaceDB = zeros(20, 20, nMax, 'uint8');

[Annie micheal]

No

[Image Analyst]

Well, give it a try.

[Annie micheal]

Its working.. thank u..

Answer 5

[manasa p]

how to display 83*86*220 data set image in mat tool

[Tain Neupane]

Same question, I want to display an image of size 512x512x150. How do I do so using imtool or imshow or other ways? I am looking for help as soon as possible. Thank you!

[Image Analyst]

You can use the volume viewer app, or you can extract a single plane and use either imtool (pops up in a new window) or imshow (uses existing axes if there is one, else makes a new one).