Images Go API Overview

Python |Java |PHP |Go

The Images Go API provides the ability to serve images directly from Blobstore, and to optionally resize or crop those images on the fly.

  1. Image formats
  2. Serving and re-sizing images from the Blobstore

Image formats

The service accepts image data in the JPEG, PNG, WEBP, GIF (including animated GIF), BMP, TIFF and ICO formats.

It can return transformed images in the JPEG, WEBP and PNG formats. If the input format and the output format are different, the service converts the input data to the output format before performing the transformation.

Serving and re-sizing images from the Blobstore

The image.ServingURL function allows you to generate a stable, dedicated URL for serving web-suitable image thumbnails. You simply store a single copy of your original image in Blobstore, and then request a high-performance per-image URL. This special URL can serve that image resized and/or cropped automatically, and serving from this URL does not incur any CPU or dynamic serving load on your application (though bandwidth is still charged as usual). Images are served with low latency from a highly optimized, cookieless infrastructure.

The URL returned by the function is always public, but not guessable; private URLs are not currently supported. If you wish to stop serving the URL, delete it using the image.DeleteServingURL function.

If you pass an image.ServingURLOptions value to the function, it returns a URL encoded with those options. If you pass nil, the function returns the default URL for the image, for example:


You can then add arguments to this URL to get the desired size and crop parameters. The available arguments are:

  • =sxx where xx is an integer from 0–1600 representing the length, in pixels, of the image's longest side. For example, adding =s32 resizes the image so its longest dimension is 32 pixels.
  • =sxx-c where xx is an integer from 0–1600 representing the cropped image size in pixels, and -c tells the system to crop the image.
// Resize the image to 32 pixels (aspect-ratio preserved)

// Crop the image to 32 pixels