Hi, i have a .mat file and i have images in that file. i need to view the each image.

I have received one file with .mat format and i need to view the images in it. could anyone please help me?

[live to l e a r n MATLAB]

In .mat files having any variables name means its easy to use imshow function

[Mohan Prasath Thirumalaisamy]

Hi Kesavan,

>> load('data.mat')
>> open('data.mat')

ans = 

      testdata: [1x67 struct]

this is what i am getting and i want to view the images.

The variable name is testdata as far as i understood and even if i give, it shows me error.

Answer 1

[Jan]

The reply "testdata = 1x67 struct array" reveals, that a struct array is replied. So please try:

storedStructure = load(fullMatFileName)
for ii = 1:numel(storedStructure)
  figure;  % Open a new figure
  image(storedStructure(ii).image);
end

[Tejashree Gore]

I'm getting this error when i run this code..

Reference to non-existent field 'image'.

[Image Analyst]

Well you may not have fields in your .mat file that were called that. You have to replace "image" with the actual name of your variable. Type

> fieldnames(storedStructure)

on the command line, or else look in the workspace variable inspector to discover what variables you stored in your .mat file. Those variables will be "fields" of the structure returned by load().

[Isha Kamleshbhai Maun]

What if the images are gray images? I get the error : color data must be numeric or logical values for "image".

[Image Analyst]

It does not matter. If there is no field of the structure "storedStructure" called "image" then the reference to storedStructure(ii).image will fail.

I suspect you have different code, a different mat file, a different question, and should have asked this in your own discussion thread.

[Walter Roberson]

image() works under the following circumstances:

• data is uint8, uint16, uint32, uint64
• data is int8, int16, int32, int64
• data is single, double
• data is logical
• data is 2D array
• data is 3D array with length of third dimension is 3

image() does not work under the following circumstances

• data is char, string, cell array, struct, graphics object
• data has complex components, even if the components are all 0

image() does not normally work for objects (in the object-oriented sense), but it is not out of the question that the designers of the object might have created an image() method

Answer 2

[Image Analyst]

storedStructure = load(fullMatFileName);

image1 = storedStructure.image1; % or whatever it's called.
image2 = storedStructure.image2; % or whatever it's called.
image3 = storedStructure.image3; % or whatever it's called.
imshow(image1, []);
imshow(image2, []);
imshow(image3, []);

[Mohan Prasath Thirumalaisamy]

Hi, thanks for the answer, but i need to give the name of each image to view it. How to do that? I mean, how to know the name in each image.

[Image Analyst]

Just type the name into the command window, or else if they're different all the time, use fieldnames to figure out the names of the arrays that are stored in the mat file, but then you'd have to use dynamic structure field names to use them.

names = fieldnames(storedStructure);

[Mohan Prasath Thirumalaisamy]

Hi load('data.mat')

testdata

testdata =

1x67 struct array with fields: image names = fieldnames(testdata)

names =

    'image'

when i type again image in command window, i am getting an image. How to get all the images

[Image Analyst]

image is a built in function name. When you type image into the command window, you are running that function. You need to pass it an image name and I don't know what you passed it. Have you looked up image and imshow in the help? Try doing

whos testdata.image
fieldnames(testdata.image)

to see if there are any members of the image member of your structure.

[Image Analyst]

Mohan, is it working now?

[Mohan Prasath Thirumalaisamy]

Hi, I am really sorry. As, I didnt see this answer. I wasnt given the exact .mat file name. That was the problem. I solved this issue on that day when i asked the question. sorry for not replying. Thanks a lot for your help.

[Shaveta Arora]

Mr. Mohan

Can u pls help me in this, my .mat file contains only one image. how to read that?

[Image Analyst]

Use the load() function. But you saw my answer so I'm not sure why it's not working for you. What went wrong?

Answer 3

[Ricky Moua]

I"m getting this error:

>>image1 = storedStructure.image1;

Reference to non-existing field 'image1'

why?

[Walter Roberson]

Whatever created storedStructure does not have a field named "image1"

I suspect that you have

storedStructure = load('SomeFileName.mat');

and then are accessing storedStructure.image1 . If so, then SomeFileName.mat just does not happen to contain a variable with that name; use fieldnames(storedStructure) to find out what it does have.

[Ricky Moua]

fieldnames(storedStructure)

ans =

1x1 cell array

{'a'}

I captured 6 frames that are saved in this filename "june14asidelights.mat". I want to loop thru them and access the 6 frames (images). Each frame is one image.

[Image Analyst]

Your mat file contains a structure and that structure has one field ONLY. And that field is called "a". We do not know what the (badly-named) "a" is (what class of variable) nor do we know what "a" contains. "a" could be a 4 or 3-D array with 6 frames in it. It could be a cell array containing one frame per cell, or it could just be some number or matrix and not at all what you expected. What does this show:

whos storedStructure.a

[Ricky Moua]

I entered the command and returns empty.

Here's the session log for my image aqusition. I set the frames per trigger to 1 and then infinite trigger. It is set to hardware trigger. As each item comes but, the camera will take an image when triggered. I'm not sure if there is a way to save those iindividual images to my local hard drive as JPEG or TIFF images.

session log:

vid = videoinput('gige',1,'BayerRG8');
src = getselectedsource(vid);
vid.FramesPerTrigger =1;
src.TriggerMode = 'On';
vid.LoggingMode = 'disk&memory';
vid.TriggerRepeat = Inf;
triggerconfig(vid,'hardware','DeviceSpecific','DeviceSpecific');
stop(vid);
a = getdata(vid);
save('/Users/.../june14asidelights.mat','a');

What would you recommend me do so that I can accomplish the goal of saving those captured images into local hard drive in either jpeg or tiff format so I can easily look at it?

[Image Analyst]

If the badly-named a is empty, then you're not getting the image and you need to debug your camera.

If you get something for a, use imwrite() instead of save(). Make sure you make up a new filename each time.

baseFileName = sprintf('Frame %d.png', frameCounter);
folder = '/Users/.../';
fullFileName = fullfile(folder, baseFileName)
imwrite(a, fullFileName);
frameCounter = frameCounter + 1;

[Ricky Moua]

Attached is the file. I ran it but getting Undefined function or variable 'frameCounter'.

Error in line 22

baseFileName = sprintf('Frame %d.png', frameCounter);

I would like to run the script and then it would capture the image based on the hardware trigger.

[Image Analyst]

You need to initialize frame counter somewhere of course. Did you do that? Do that before your loop starts. You might call getsnapshot() instead of getdata().

[Ricky Moua]

Enclosed is the complete script. I'm getting an error "A timeout occurrred during GETSNAPSHOT".

I want the script to take an image whenever the hardware is being trigged and I only want 5 images for now.