Storing Large Images In Power BI Datasets

Jason Thomas and Gerhard Brueckl have both blogged on the subject of storing images as text inside a Power BI dataset:

Since they wrote those posts, however, Power BI has added the ability to set the Data Category property on measures as well as columns in tables. This means it is now possible to have the output of a DAX measure displayed as an image in a Power BI report and this in turn opens up a lot of new possibilities – including the ability to work around the maximum size of a text value that can be loaded into Power BI (see my previous blog post for more details) and therefore work with larger images.

Here’s a rather lovely picture of a rose:

2014-08-18 17.02.10_20Pct

The original is about 2.1MB; I have a folder on my PC where different versions of this picture, saved at different percentages of the original size, are stored:


Using the technique that Gerhard wrote about, where the pictures can be stored as text in a single cell in a Power BI dataset and then displayed (in this case I’m using the Image by CloudScope custom visual) some truncation of the image occurs even with the smallest files because of the 32766 character limit on the length of a text value that can be loaded into Power BI. Here’s what you see when you display the version of the picture that is 20% of the original size, a file of only 113KB:


To work around this, what you need to do is to split the text representation of the image up into multiple smaller text values stored across multiple rows, each of which is less than the 32766 character limit, and then reassemble them in a DAX measure after the data has been loaded.

Splitting the text up in M is actually not that hard, but it is hard to do efficiently. Here’s an example of an M query that reads all the data from all of the files in the folder above and returns a table:

    //Get list of files in folder
    Source = Folder.Files("C:\Users\Chris\Documents\PQ Pics"),
    //Remove unnecessary columns
    RemoveOtherColumns = Table.SelectColumns(Source,{"Content", "Name"}),
    //Creates Splitter function
    SplitTextFunction = Splitter.SplitTextByRepeatedLengths(30000),
    //Converts table of files to list
    ListInput = Table.ToRows(RemoveOtherColumns),
    //Function to convert binary of photo to multiple
    //text values
    ConvertOneFile = (InputRow as list) =>
            BinaryIn = InputRow{0},
            FileName = InputRow{1},
            BinaryText = Binary.ToText(BinaryIn, BinaryEncoding.Base64),
            SplitUpText = SplitTextFunction(BinaryText),
            AddFileName = List.Transform(SplitUpText, each {FileName,_})
    //Loops over all photos and calls the above function
    ConvertAllFiles = List.Transform(ListInput, each ConvertOneFile(_)),
    //Combines lists together
    CombineLists = List.Combine(ConvertAllFiles),
    //Converts results to table
    ToTable = #table(type table[Name=text,Pic=text],CombineLists),
    //Adds index column to output table
    AddIndexColumn = Table.AddIndexColumn(ToTable, "Index", 0, 1)

In my next post I’ll show you my original version of this query, explain why it was slow, and try to explain how the version above works and why it is much faster.

Here’s what the query above returns:


The Pic column contains the split text values, each of which are less than the 32766 character limit, so when this table is loaded into Power BI no truncation occurs. The index column is necessary because without it we won’t be able to recombine all the split values in the correct order.

The only thing left to do is to create a measure that uses the DAX ConcatenateX() function to concatenate all of the pieces of text back into a single value, like so:

Display Image = 
    HASONEVALUE('PQ Pics'[Name]),
    "data:image/jpeg;base64, " & 
        'PQ Pics', 
        'PQ Pics'[Pic],
        'PQ Pics'[Index],

…set the data category of this measure to be “Image URL”:


…and then display the value of the image in a report:



Unfortunately, as I also mentioned in my previous post, most DAX functions (and that includes ConcatenateX()) have a limit of around 2.1 million characters so the original 2.1MB file still can’t be displayed, alas:


However, I do think this technique will be useful because it allows you to work with much larger pictures than before.

It can also be useful in other situations too. I recently came across a great new custom visual called PDF Viewer that can display PDF files stored in text form in a Power BI report:


The example file for this visual shows how a large PDF file can be split across two columns in a table; the technique I describe here is a more practical solution to this problem.

44 responses

  1. This looks great, perhaps I am doing something wrong but when I drop your code in as a querie while changing the folder path it doesn’t generate a table. I could potentially split up the code to make it work but wanted to check if there’s something obvious I am missing. I have it working from Gerhard’s post.

    • Ignore this!

      Advanced editor did the trick was trying to build it as a function before.

  2. Pingback: Storing Large Images in Power BI – Curated SQL

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  4. Thanks Chris! now its ok! (using the custon visual “Image by CloudScope”)

  5. Hi Chris,

    Just to check, this method is only for “Import” or it is works in “Direct Query” mode as well?


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  8. I’ve followed the steps but when I try to drag the ‘Display Image’ field to the image field in the Chiclet Slicer visual, it doesn’t take it. Does this not work with Chiclet Slicer?

    I have images loaded but, despite them being around 50kb or less, they are truncated so that the bottom section is missing from some of the images.

    • Apologies, my second sentence above meant that using a different method I can get images loaded but they do not display properly. I can’t get images to display at all with the method described in the article above.

  9. Hi Chris,
    This topic of query optimization should be much more explored. Just a comparison with DAX show how much material there is for this language, from books to blog posts, while for M there is only a few sparsed sources, as your blog and some others for example.
    At least from my experience, M is as important as DAX, but many times I found it too slow to process even a small amount of data, reading a file multiple times for example. M should be the as fast and efficient as possible, but I don’t if this a implementation or end user fault.

    After this digression, what I would like to know is if the operation on lists, as in this post, is generally faster than operations on tables, and if this approach solves the multiple file readings problem.


  10. I try it and work perfectly. But just one more question … does this work with the BI service on the cloud when it is refreshed

  11. hey Chris, is there a way to use binary image from a SQLdatabase instead of the actual image?

    • My first reaction is to say no – this feature was actually removed from the product some time ago, I think because it was a security risk. However there might be a way around it… I would need to test some things first.

      • Looked into it myself and it is possible it’s the same code just the source and the selected columns are different

  12. Hi Chris. First of all – thanks a lot for this post.
    I have a problem with using yours and Gerhard’s approaches to show images in cards. When I am using default “multi-row card” visual in power bi I see images as images when they are uploaded using public URL. However if I try to use your method and upload images from a local folder I will see a plain text instead of picture. Whereas in a “table” visual I see images as images in both cases. Any ideas what might be wrong with card visual?

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  14. Hey Chris, thanks for this post.

    I want to make the image base64 results appear on one row.

    Would it be possible to convert the PIC columns to rows so that each image has a single row with multiple columns for base64 values and then make the DAX statement concatenate each column instead of each row?

    • Why would you want to do this? The trouble with this approach would be that you would have an arbitrary number of columns to combine the data from, and that would be impossible to do in DAX; splitting the data across multiple rows is the only way to concatenate the text easily.

  15. Chris, master, you can give an example using connection to an sql database that is where I have my images to give me a more general idea of ​​how to interact.

    It will be a great help, a big hug and my usual respects.

  16. Hi Chris, Can you guide me here. I have 1000 image folders for 1000 employees stored in drive, each folder having max of 6 images each. I have created a report in Powerbi and need to show images according to respective row of employees.
    is there any ideal approach to achieve this.

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  18. Awesome post Chris,

    However, everything seems to check out and the table is populated with indexed strings but after creating the measure, enabling image url and inputting the image in CloudScope visual, nothing appears. Just an empty cell. First time working with M so maybe its a configuration thing but I added a second file and it was automatically sharded and indexed so im not sure what the issue is…

      • Pulling the arrow to decrease the height wouldn’t scale the image, but I discovered decreasing the width will scale the image down. Also facepalm because in my initial comment I was using a PNG file. Thank you so much for this tutorial!

  19. Hi Chris,
    I’m getting an error on line 12 of your M Query “Token Literal is Expected” and the ampersand sign has a red squiggle under it. Any idea why?

  20. Pingback: Chris Webb's BI Blog: Power Query Performance And Expanding Columns Chris Webb's BI Blog

  21. Pingback: Powering Up MYOB’s New Foreign Currency functionality(Part 2) – Five Ledger

  22. Brilliant Solution! I was able to get images up to 1Mb but I am facing a more advanced problem. How do we deal with multiple image files? I have 4 images in the same folder which would also need to be brought in.

  23. Thanks so much for this Chris; does the code in the measure need to be changed in order to display different images, I’m only get one image to display?

  24. Yet another fantastic post. Thanks. I have a question that is triggered by this post but is only remotely related to it. Hope you don’t mind if I ask it anyway.
    I have a custom connector that reads data from an accounting system by wrapping a URL in OData.Feed. The custom connector handles the OAuth2 token exchange and everything works well. OData.Feed accepts “Concurrent = false” as option so I never get asynchronous requests messing up the OAuth2 tokens. Everything fine so far.
    Among other data, OData.Feed returns URLs to PDFs of invoices that I would like to process with the technique in your post (as I said: remotely related). The URLs look something like and do not work if I wrap them in OData.Feed. Instead I am using Web.Contents() and process the result with your technique. It works for fetching a single PDF.
    However… There are some 30.000 PDFs, each with its own URL. I have not been able to get Web.Contents() to execute synchronously (there is no “Concurrent = false” option). As a result, things run async and the OAuth2 token dance doesn’t work anymore because there is another call before the refresh-token has been received.
    My question: Is there a way to do sychronous calls to Web.Contents() ?

    Any help or pointer is highly appreciated.

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