Loading images from a .MAT file

i have this function which i used to save a folder of images into a .MAT file as a database. Now i want to load the images from the data to use them but its a struct so i tried converting using struct2cell and that didn't get me anywhere. I seen about 3 different ways to get this to work but non seem to work which made me thing maybe i saved them wrong?

So i want to make a loop that loads all images from this database. all images have the same dimensions and file type .jpg

   folder = 'F:\matlab\face\data';

ListOfImageNames = {};
ImageFiles = dir([folder '/*.*']); % Get all files.
for Index = 1:length(ImageFiles)
  baseFileName = ImageFiles(Index).name;
  [folder, name, extension] = fileparts(baseFileName);
  extension = upper(extension);
  % Let's save just those we are interested in:
  switch lower(extension)
  case {'.png', '.bmp', '.jpg', '.tif', '.avi'}
    % Allow only PNG, TIF, JPG, or BMP images
    ListOfImageNames = [ListOfImageNames baseFileName];
  otherwise
  end
end

save('F:\matlab\face\testimagebase.mat','ListOfImageNames');

Answer 1

[Jacob Halbrooks]

The code shown only saves the names of the image files and not the image data itself. This is because the variable 'ListOfImageNames' is a cell array of names, and SAVE just stores it in the MAT-file as such.

If you want to save the actual image data, you should call IMREAD on each image to get its data into MATLAB, and then use SAVE for the actual data. One way to do this is to create a struct and add fields to this struct as you find and read images. Here's how that might look, based off of your code:

   function saveImages(folder)

   ListOfImageNames = {};
   ImagesToSave = struct();
   ImageFiles = dir([folder '/*.*']); % Get all files.
   for Index = 1:length(ImageFiles)
       baseFileName = ImageFiles(Index).name;
       [folder, name, extension] = fileparts(baseFileName);
       extension = upper(extension);
       % Let's save just those we are interested in:
       switch lower(extension)
           case {'.png', '.bmp', '.jpg', '.tif', '.avi'}
               % Allow only PNG, TIF, JPG, or BMP images
               ListOfImageNames = [ListOfImageNames baseFileName];
               ImagesToSave.(name) = imread(baseFileName);
           otherwise
       end
   end
   save('testimagebase.mat','-struct','ImagesToSave');

Now if you call LOAD on your MAT-file, you will be returned the same structure that you originally saved, with a field for each image containing its data:

   >> saveImages(pwd)
   >> myimages=load('testimagebase.mat')

   myimages = 

           image1: [2178x2448x3 uint8]
         myimage2: [676x1088x3 uint8]

[Tony]

when i load it shows

a1 =

    ListOfImageNames: {1x25 cell}

it does not save in an array as your read out

tried imshow(a2.ListOfImageNames(1))

does not read it as

??? Error using ==> iptcheckinput Function IMAGEDISPLAYVALIDATEPARAMS expected its first input, I, to be one of these types:

double, single, uint8, uint16, uint32, int8, int16, int32, logical

Instead its type was cell.

[Image Analyst]

ListOfImageNames is a cell array. Somehow it got attached as a field of a structure called a1, maybe a1 was the return argument of a load()???? If so, you might want to do

a1 = load(matFileName);
ListOfImageNames = a1.ListOfImageNames;
% Now read in an image
folder = pwd; % or whatever it really is.
% Prepend folder to base file name.
fullFileName = fullfile(folder, ListOfImageNames{1});
myImage = imread(fullFileName); % Read it in.
imshow(myImage); % Display it.

[Tony]

thank you but isn't this kind of going backwards i want the actual image in the .mat file which i believe Jacob's has done. I would like to be able to load it as an array to have a for loop cycle through them

[Image Analyst]

Jacob saved the "ImagesToSave" variable, which are the actual images in a cell array. Apparently you also saved the variable "ListOfImageNames" (which is a list of strings, not image arrays), and you were having trouble recalling that variable (if you check your comment just before mine), so that's what I was trying to help you with.

[poongothai rajan]

dear image analyst ..when i run your code i am getting this error..can u plese clarify it

"Reference to non-existent field 'ListOfImageNames'."

[Jyoti Arora]

Dear Image Analyst After Loading the .mat file if I am getting this output, groundTruth: {[1x1 struct] [1x1 struct] [1x1 struct] [1x1 struct] [1x1 struct] [1x1 struct] [1x1 struct]} how can I use it further in my code. Each struct represents segment of an image and I want to evaluate for my segmentation results.

Answer 2

[poongothai rajan]

can u please anyone help how to convert the .mat file into image file..thanks in advance

Answer 3

[Shaveta Arora]

i have .mat one file which is 1x1 struct. how to read the image from this.

[Image Analyst]

Call load to read the mat file into a structure:

storedStruct = load(yourFileName);

Now, if you had a structure that you stored when you called save() to create the mat file, then that structure will be a field of the storedStuct variable. You can extract it into a variable if you want:

myStruct = storedStruct.myStruct;