how to load random image from folder

Hello. I have 4 images in 1 folder and I have to load them randomly. I tried to do this.

>> a=dir(['C:\Users\Desktop\Crossroad\vehicles' '/*.png'])

and then randomly load one of 4 images

im=imread(a(randi(4)).name)

but matlab gives me an error:

Error using imread (line 349)

File "white_car.PNG" does not exist.

It. wrotes that files doesnt exist, but it actually does..Does anyone know how to write it properly? Many thanks.

Answer 1

[Image Analyst]

You need to use fullfile because a(index).name does not include the folder.

folder = 'C:\Users\Desktop\Crossroad\vehicles'
fileList = dir(fullfile(folder, '/*.png'))
randomIndex = randi(length(fileList), 1, 1) % Get random number.
fullFileName = fullfile(folder, fileList(randomIndex).name)
img = imread(fullFileName);

[Miroslav Jiránek]

Thank you, sir. It helps a lot

[Adam Bodis]

Error using randi

First input must be a positive scalar integer value IMAX, or two integer values [IMIN IMAX] with IMIN less than or equal to IMAX.

Error in sem_praca_bodis (line 13)

randomIndex = randi(length(fileList), 1, 1); % Get random number.

i have this type of error. Any help please?

[Image Analyst]

fileList is empty and so the length of it is zero. You must give a file name pattern to dir() that will load the variable with some file information.

[ANKIT MAURYA]

What if i need to present randomly different images on different trials from a set of pictures stored in a folder ?

[Image Analyst]

@ANKIT MAURYA use randperm

sortOrder = randperm(numel(fileList));

unless you want to allow repeats, then use randi.