Pilbox

An image resizing application server

View the Project on GitHub agschwender/pilbox

Pilbox

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Pilbox is an image processing application server built on Python's Tornado web framework using the Python Imaging Library (Pillow). It is not intended to be the primary source of images, but instead acts as a proxy which requests images and resizes them as desired.

Setup

Dependencies

Pilbox highly recommends installing libcurl and pycurl in order to get better HTTP request performance as well as additional features such as proxy requests and requests over TLS. Installed versions of libcurl should be a minimum of 7.21.1 and pycurl should be a minimum of 7.18.2. Furthermore, it is recommended that the libcurl installation be built with asynchronous DNS resolver (threaded or c-ares), otherwise it may encounter various problems with request timeouts (for more information, see CURLOPT_CONNECTTIMEOUT_MS and comments in curl_httpclient.py

Install

Pilbox can be installed with pip

$ pip install pilbox

Or easy_install

$ easy_install pilbox

Or from source

$ git clone https://github.com/agschwender/pilbox.git

Packaged with Pilbox is a Vagrant configuration file which installs all necessary dependencies on a virtual box using Ansible. See the Vagrant documentation and the Ansible documentation for installation instructions. Once installed, the following will start and provision a virtual machine.

$ vagrant up
$ vagrant provision

To access the virtual machine itself, simply...

$ vagrant ssh

When running via Vagrant, the application is automatically started on port 8888 on 192.168.100.100, i.e.

http://192.168.100.100:8888/

Running

To run the application, issue the following command

$ python -m pilbox.app

By default, this will run the application on port 8888 and can be accessed by visiting:

http://localhost:8888/

To see a list of all available options, run

$ python -m pilbox.app --help
Usage: pilbox/app.py [OPTIONS]

Options:

  --allowed_hosts            list of allowed hosts (default [])
  --allowed_operations       list of allowed operations (default [])
  --background               default hexadecimal bg color (RGB or ARGB)
  --client_key               client key
  --client_name              client name
  --config                   path to configuration file
  --content_type_from_image  override content type using image mime type
  --debug                    run in debug mode (default False)
  --expand                   default to expand when rotating
  --filter                   default filter to use when resizing
  --help                     show this help information
  --implicit_base_url        prepend protocol/host to url paths
  --max_operations           maximum operations to perform (default 10)
  --max_requests             max concurrent requests (default 40)
  --max_resize_height        maximum resize height (default 15000)
  --max_resize_width         maximum resize width (default 15000)
  --operation                default operation to perform
  --optimize                 default to optimize when saving
  --port                     run on the given port (default 8888)
  --position                 default cropping position
  --progressive              default to progressive when saving
  --proxy_host               proxy hostname
  --proxy_port               proxy port
  --quality                  default jpeg quality, 0-100 or keep
  --timeout                  timeout of requests in seconds (default 10)
  --validate_cert            validate certificates (default True)

Calling

To use the image processing service, include the application url as you would any other image. E.g. this image url

<img src="http://i.imgur.com/zZ8XmBA.jpg" />

Would be replaced with this image url

<img src="http://localhost:8888/?url=http%3A%2F%2Fi.imgur.com%2FzZ8XmBA.jpg&w=300&h=300&mode=crop" />

This will request the image served at the supplied url and resize it to 300x300 using the crop mode. The below is the list of parameters that can be supplied to the service.

General Parameters

Resize Parameters

Region Parameters

Rotate Parameters

Security-related Parameters

The url parameter is always required as it dictates the image that will be manipulated. op is optional and defaults to resize. It also supports a comma separated list of operations, where each operation is applied in the order that it appears in the list. Depending on the operation, additional parameters are required. All image manipulation requests accept fmt, opt and q. fmt is optional and defaults to the source image format. opt is optional and defaults to 0. q is optional and defaults to 90. To ensure security, all requests also support, client and sig. client is required only if the client_name is defined within the configuration file. Likewise, sig is required only if the client_key is defined within the configuration file. See the signing section for details on how to generate the signature.

For resizing, either the w or h parameter is required. If only one dimension is specified, the application will determine the other dimension using the aspect ratio. mode is optional and defaults to crop. filter is optional and defaults to antialias. bg is optional and defaults to fff. pos is optional and defaults to center. retain is optional and defaults to 75.

For region sub-selection, rect is required. For rotating, deg is required. expand is optional and defaults to 0 (disabled). It is recommended that this feature not be used as it typically does not produce high quality images.

Note, all built-in defaults can be overridden by setting them in the configuration file. See the configuration section for more details.

Examples

The following images show the various resizing modes in action for an original image size of 640x428 that is being resized to 500x400.

Clip

The image is resized to fit within a 500x400 box, maintaining aspect ratio and producing an image that is 500x334. Clipping is useful when no portion of the image can be lost and it is acceptable that the image not be exactly the supplied dimensions, but merely fit within the dimensions.

Clipped image

Crop

The image is resized so that one dimension fits within the 500x400 box. It is then centered and the excess is cut from the image. Cropping is useful when the position of the subject is known and the image must be exactly the supplied size.

Cropped image

Fill

Similar to clip, fill resizes the image to fit within a 500x400 box. Once clipped, the image is centered within the box and all left over space is filled with the supplied background color. Filling is useful when no portion of the image can be lost and it must be exactly the supplied size.

Filled image

Scale

The image is clipped to fit within the 500x400 box and then stretched to fill the excess space. Scaling is often not useful in production environments as it generally produces poor quality images. This mode is largely included for completeness.

Scale image

Testing

To run all tests, issue the following command

$ python -m pilbox.test.runtests

To run individual tests, simply indicate the test to be run, e.g.

$ python -m pilbox.test.runtests pilbox.test.signature_test

Signing

In order to secure requests so that unknown third parties cannot easily use the resize service, the application can require that requests provide a signature. To enable this feature, set the client_key option. The signature is a hexadecimal digest generated from the client key and the query string using the HMAC-SHA1 message authentication code (MAC) algorithm. The below python code provides an example implementation.

import hashlib
import hmac

def derive_signature(key, qs):
    m = hmac.new(key, None, hashlib.sha1)
    m.update(qs)
    return m.hexdigest()

The signature is passed to the application by appending the sig parameter to the query string; e.g. x=1&y=2&z=3&sig=c9516346abf62876b6345817dba2f9a0c797ef26. Note, the application does not include the leading question mark when verifying the supplied signature. To verify your signature implementation, see the pilbox.signature command described in the tools section.

Configuration

All options that can be supplied to the application via the command line, can also be specified in the configuration file. Configuration files are simply python files that define the options as variables. The below is an example configuration.

# General settings
port = 8888

# Set client name and key if the application requires signed requests. The
# client must sign the request using the client_key, see README for
# instructions.
client_name = "sample"
client_key = "3NdajqH8mBLokepU4I2Bh6KK84GUf1lzjnuTdskY"

# Set the allowed hosts as an alternative to signed requests. Only those
# images which are served from the following hosts will be requested.
allowed_hosts = ["localhost"]

# Request-related settings
max_requests = 50
timeout = 7.5

# Set default resizing options
background = "ccc"
filter = "bilinear"
mode = "crop"
position = "top"

# Set default rotating options
expand = False

# Set default saving options
format = None
optimize = 1
quality = 90

Tools

To verify that your client application is generating correct signatures, use the signature command.

$ python -m pilbox.signature --key=abcdef "x=1&y=2&z=3"
Query String: x=1&y=2&z=3
Signature: c9516346abf62876b6345817dba2f9a0c797ef26
Signed Query String: x=1&y=2&z=3&sig=c9516346abf62876b6345817dba2f9a0c797ef26

The application allows the use of the resize functionality via the command line.

$ python -m pilbox.image --width=300 --height=300 http://i.imgur.com/zZ8XmBA.jpg > /tmp/foo.jpg

If a new mode is added or a modification was made to the libraries that would change the current expected output for tests, run the generate test command to regenerate the expected output for the test cases.

$ python -m pilbox.test.genexpected

Deploying

The application itself does not include any caching. It is recommended that the application run behind a CDN for larger applications or behind varnish for smaller ones.

Defaults for the application have been optimized for quality rather than performance. If you wish to get higher performance out of the application, it is recommended you use a less computationally expensive filtering algorithm and a lower JPEG quality. For example, add the following to the configuration.

# Set default resizing options
filter = "bicubic"
quality = 75

Extension

While it is generally recommended to use Pilbox as a standalone server, it can also be used as a library. To extend from it and build a custom image processing server, use the following example.

#!/usr/bin/env python

import tornado.gen

from pilbox.app import PilboxApplication, ImageHandler, main


class CustomApplication(PilboxApplication):
    def get_handlers(self):
        return [(r"/(\d+)x(\d+)/(.+)", CustomImageHandler)]


class CustomImageHandler(ImageHandler):
    def prepare(self):
        self.args = self.request.arguments.copy()

    @tornado.gen.coroutine
    def get(self, w, h, url):
        self.args.update(dict(w=w, h=h, url=url))

        self.validate_request()
        resp = yield self.fetch_image()
        self.render_image(resp)

    def get_argument(self, name, default=None):
        return self.args.get(name, default)


if __name__ == "__main__":
    main(app=CustomApplication())

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