Auto generation of thumbnails or preview of images when posting to Azure blob storage

Question

I am posting pictures to Azure blob storage. As I am storing full resolution images, I want to maintain a separate collection(s) of thumbnails(or previews) of the images. Is it possible to write a script(or a hook) where when an image is uploaded to the blob storage, the thumbnail of the image is also automatically saved.

Please inform if there's a way to script this.

I don't want to do the resizing on the client side or on the server side. I am using SAS to enable the client to upload the images to blob storage directly. I can send the image to the Mobile Service(server) I am running where the image can be resized and uploaded to the blob storage. But I don't want to overload the server with these calls.

jakobandersen jakobandersen · Accepted Answer · 2015-05-16T07:28:24

Yes that is indeed possible, you can do this by deploying a WebJob using a BlobTrigger that takes the inputstream for the newly created blob and let you modify it to an output blob, the code would look like this using the excellent imageresizing.net library:

public static void ResizeMicroImages(
        [BlobTrigger("orig/{name}.{ext}")] Stream input,
        [Blob("90x126/{name}.png", FileAccess.Write)] Stream output
){
        ImageBuilder.Current.Build(new ImageJob(input, output, new Instructions()
        {
            AutoRotate = true,
            Width = 90,
            Height = 126,
            OutputFormat = OutputFormat.Png,
        }));
    }

However in our setup we have seen problems when we reach a lot of pictures with the webjob throwing OutOfMemoryExceptions when it do the initial check for unprocessed blobs, but that might be specific to our setup (We have a lot of pictures). We changed to manually adding a message to a storage queue and instead have a webjob process it using a QueueTrigger.

Auto generation of thumbnails or preview of images when posting to Azure blob storage

2 Answers