ImageDataStore read issue -- works sometimes, sometimes not

Question

Mark Zarella 2021-1-7

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https://ww2.mathworks.cn/matlabcentral/answers/711148-imagedatastore-read-issue-works-sometimes-sometimes-not

回答： Steven Lord 2021-2-4

I'm getting the below error when trying to read from an image datastore, manipulate, and write. The strange part is that I can read the file using imread perfectly fine. I'm literally copying the filename from the error message and pasting it into an imread command and it works. Any idea how I can troubleshoot this?

Error using matlab.io.datastore.ImageDatastore/read (line 77)
Unable to read file: <redacted filename>
Error in matlab.io.datastore.FileWritable/writeSerial (line 14)
        [data, readInfo] = read(dsCopy);
Error in matlab.io.datastore.FileWritable/writeParallel (line 45)
            parfor (ii = 1 : size(files,1), M)
Error in matlab.io.datastore.FileWritable/writeall (line 272)
                writeParallel(ds, location, files, nvStruct);
Error in augment_images (line 101)
                    writeall(subds, [options.Filenames.OutputDir options.Mag],
                    'FilenameSuffix',suffix,
                    'OutputFormat',options.Filenames.OutputFormat,
                    'UseParallel',true);
Caused by:
    Error using
    matlab.io.datastore.exceptions.decorateCustomFunctionError>generateReadFcnError
    (line 103)
    Error using ReadFcn @readDatastoreImage for file:
        <redacted filename>
    Error using imread>get_full_filename (line 564)
    Cannot open file "<redacted filename>" for reading.
    You might not have read permission.
    Error in imread (line 374)
        fullname = get_full_filename(filename);
    Error in readDatastoreImage (line 12)
    data = imread(filename);

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Answer 1

Mahesh Taparia 2021-2-4

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Hi

It seems either the folder path is inappropriate or the files are not in the supported image format. Correct the folder path of the files, it will work.

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Mark Zarella 2021-2-4

编辑：Mark Zarella 2021-2-4

That's what I thought originally as well. But I've confirmed the folder path is correct and that the file formats are supported. The way I did this is by manually running the imread function on the SAME file path and it works fine. And I did this programmatically to ensure the difference wasn't due to manual entry.

Mahesh Taparia 2021-2-4

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Hi

Can you upload a sample image from your dataset?

Also let me know, if the below code is working your not.

imds = imageDatastore(fullfile(matlabroot,'toolbox','matlab'),...
'IncludeSubfolders',true,'FileExtensions','.tif','LabelSource','foldernames')

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Answer 2

Steven Lord 2021-2-4

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If you try running imread inside a parfor loop rather than at the MATLAB prompt, does it throw an error? I'm wondering if the parallel pool is running the workers on a cluster as a different user that does not have the necessary permissions to access the data files.