Processing image from the blob GAE

Question

I managed to store a picture in the Google App engine blob (I can see it in the Blob Viewer from the dashboard, and also in my app using a serving handler).. However, now that i have this picture there..i want to resize it while serving it to the client...Problem is that i can't do that...I can't make an Image out of that blob...This is my code :

from google.appengine.api import images

from google.appengine.ext import blobstore      
from google.appengine.ext.webapp import blobstore_handlers  
....
class Image(webapp2.RequestHandler):
def get(self,id):
    product = Product.by_id(int(id))
    logging.info('pic key is' + str(product.small_pic.key()))
    img = images.Image(blob_key=str(product.small_pic.key()))
    img.im_feeling_lucky() # do a transform, otherwise GAE complains.

    img.execute_transforms(output_encoding=images.JPEG,quality=1)
    if img:
        self.response.headers['Content-Type'] = 'image/png'
        self.response.out.write(img)
    else:
        self.error(404)

The code from above is taken from this thread : GAE: How to get the blob-image height

When i run the code from above ex /img/373 i get the error :

The image "http:..../img/373" cannot be displayed because it contains errors How can i do this ?..What i want is to find out way to transform that blob in an image and then process the image...

Answer 1

You don't need to pipe that image through your application. The gae has a service for resizing images:

from google.appengine.api.images import get_serving_url
url = get_serving_url( "blobkey")

Then append one of https://developers.google.com/appengine/docs/python/images/functions#imgsize values to that url and you're done.

Answer 2

The first answer was close. This slight refinement lets you adjust the size explicitly:

from google.appengine.api.images import get_serving_url
url = get_serving_url( "blobkey",size=1024)

In the above code, size=1024 dynamically resizes the source blob image to be 1024 pixels on the longest side while maintaining the original proportion of the image.