HTTP API server for image thumbnailing, editing and format conversion
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README.md

HTTP Thumbnailer

Stateless HTTP API server for image thumbnailing, editing and format conversion.

It is using ImageMagick or GraphicsMagick via RMagick gem as the image processing library.

Features

  • thumbnailing images with different aspect ratio keeping methods
  • applying image edits like rotate, crop, blur, pixelate, etc.
  • identification of image format and size
  • support of many input and output formats
  • efficient API for generating multiple thumbnails from single input image with just one request
  • completely stateless
  • many image scaling and loading performance optimizations
  • efficient memory usage
  • memory limits and disk memory offloading support
  • custom plugin support
  • based on Unicorn HTTP server with UNIX socket communication support

Changelog

1.3.0

  • added edits support
  • added performance statistics
  • added plugin support
  • switches to control optimizations
  • using downsampling by default when image gets upscaled on load

1.2.0

  • added float-x and float-y option support
  • added interlace option support
  • syslog logging
  • transaction ID tracking

1.1.0

  • added identification API for image mime type and size identification
  • stripping user meta data from input image further reducing output image size
  • providing image size headers for input image and all generated thumbnails
  • X-Input-Image-Content-Type header is now deprecated in favour of X-Input-Image-Content-Type
  • not using ImageMagick for input image mime type resolution since it is accessing disk and behaves very inefficiently

Installing

You will need the following system packages installed: imagemagick, pkg-config and make. For PNG support install libpng. You may want to consult ImageMagick installation guide for more information on supported formats and required libraries.

For Arch Linux you can use this commands:

pacman -S imagemagick
pacman -S libpng
pacman -S pkg-config
pacman -S make

Then you can install the gem as usual:

gem install httpthumbnailer

Optionally install Ruby client library and tool:

gem install httpthumbnailer-client

Usage

Getting started

# install httpthumbnailer (see above)
# install httpthumbnailer-client
gem install httpthumbnailer-client

# start thumbnailing server in foreground (to stop hit Ctlr-C)
httpthumbnailer --foreground --verbose

# in another console thumbnail to standard output
cat ~/Pictures/compute.jpg | httpthumbnailer-client -t crop,100,200,png > thumbnail.png

# generate multiple thumbnails
cat ~/Pictures/compute.jpg | httpthumbnailer-client -t crop,100,200,jpeg,quality:100 -t pad,200,200,png thumbnail1.jpg thumbnail2.png

# applay edits to the image and thumbnail - pixelate middle of the image and draw blue rectangle at the bottom of it
cat ~/Pictures/compute.jpg | httpthumbnailer-client -t 'fit,280,280,png!pixelate,0.3,0.2,0.4,0.4!rectangle,0.04,0.8,0.92,0.17,color:blue' > thumbnail.png

Ruby API client

In this example we use httpthumbnailer-client gem CLI tool that will use HTTP API of the server to generate thumbnails.

Running the server

HTTP Thumbnailer uses worker based server model thanks to Unicorn HTTP server gem.

To start the thumbnailer use httpthumbnailer command. By default it will start in background and will spawn CPU core number + 1 number of worker processes. It will be listening on localhost port 3100.

To start in foreground with verbose output use httpthumbnailer --verbose --foreground. To see available switches and options use httpthumbnailer --help.

When running in background the master server process will store it's PID in httpthumbnailer.pid file. You can change pid file location with --pid-file option. If running as root you can use --user option to specify user with whose privileges the worker processes will be running.

Logging

httpthumbnailer logs to httpthumbnailer.log file in current directory by default. You can change log file location with --log-file option and verbosity with --verbose or --debug switch.

Additionally httpthumbnailer will log requests in common NCSA format to httpthumbnailer_access.log file. Use --access-log-file option to change location of access log.

Syslog logging can be enabled with --syslog-facility option followed by name of syslog facility to use. When enabled log files are not created and both application logs and access logs are sent to syslog. Access logs will gain meta information that will include "type":"http-access" that can be used to filter access log entries out from application log entries.

With --xid-header option name of HTTP request header can be specified. Value of this header will be logged in meta information tag xid along side all request related log entries.

Using --perf-stats switch will enable logging of performance statistics. This log entries will be logged with "type":"perf-stats".

Thumbnailing methods

For method you can use one of the following value:

  • fit - fit image within given dimensions keeping aspect ratio
  • crop - cut image to fit within given dimensions keeping aspect ratio
  • pad - fit resize image and pad image with background colour to given dimensions keeping aspect ratio
  • limit - fit resize image to given dimensions if it is larger than that dimensions

Supported formats

List of supported formats can be displayed with httpthumbnailer --formats. Optionally format input can be used to use the same thumbnail format as input image.

Thumbnail width and height

Width and height values are in pixels and are interpreted depending on method used. input string can be used for width and/or height to use input image width or height.

Thumbnail options

Following options can be used with thumbnail specification:

  • quality - set output image quality; this is format specific: for JPEG 0 is maximum compression and 100 is maximum quality, for PNG first digit is zlib compression level and second one is filter level
  • background-color - color in HTML notation or textual description ('red', 'green' etc.) used for background when processing transparent images or padding; by default white background is used
  • float-x and float-y - value between 0.0 and 1.0; can be used with crop and pad methods to move cropping view or image over background left to right or top to bottom (0.0 to 1.0); both default to 0.5 centering the view or image
  • interlace - one of UndefinedInterlace, NoInterlace, LineInterlace, PlaneInterlace, PartitionInterlace, GIFInterlace, JPEGInterlace, PNGInterlace; some formats support interlaced output format; use JPEGInterlace or LineInterlace or PlaneInterlace with jpeg format to produce progressive JPEG; defaults to NoInterlace

Edits

Edits are applied on input image (after possibly being downsampled) and before the final thumbnail is generated. Relative vector values are relative to input image dimensions (width and hight), scalar values are relative to input image diagonal. This way edits will look more or less the same no matter what the input or output image resolution is. Also client does not need to know the resolution of input image.

One or more edits can be used with thumbnail specification:

  • resize_crop - cut image to fit within given dimensions keeping aspect ratio
    • arguments: width, height - dimensions to resize and crop image to in pixels
    • options:
      • float-x, float-y - value between 0.0 and 1.0; move cropping view left to right or top to bottom (0.0 to 1.0); default: 0.5 (center)
  • resize_fit - fit image within given dimensions keeping aspect ratio
    • arguments: width, height in pixels
  • resize_limit - same as resize_fit but applied only if image is larger than given dimensions
    • arguments: width, height - dimension to limit image to in pixels
  • crop
    • arguments: x, y, width, height - values between 0.0 and 1.0; region of image starting from relative position to image width from left (x) and height from top (y) with relative width and height
  • pixelate - pixelate (sample) given region of image
    • arguments: box_x, box_y, box_widthd, box_height - values between 0.0 and 1.0; region of image starting from relative position to image width from left (x) and height from top (y) with relative width and height
    • options:
      • size - size of the pixel (relative to imgae diagonal); default: 0.01
  • blur - blur region of image
    • arguments: x, y, width, height - values between 0.0 and 1.0; region of image starting from relative position to image width from left (x) and height from top (y) with relative width and height
    • options:
      • sigma - amount of blur (relative to imgae diagonal); resulting value is capped to 50 pixels
      • radius - radius of the blur (0.0 - calculated for given sigma) (relative to image diagonal); resulting value is capped to 50 pixels; default: 0.0
  • rectangle - draw rectangle over image
    • arguments: box_x, box_y, box_width, box_height - values between 0.0 and 1.0; rectangle over image starting from relative position to image width from left (x) and height from top (y) with relative width and height
    • options:
      • color - color of the rectangle; default: black
  • rotate - rotate image clockwise by given angle filling any new image surface with color
    • arguments: angle - rotation angle in degree
    • options:
      • background-color - color of the background (when not 90x rotation is used); default: thumbnail background-color option or transparent

API

Single thumbnail API

To generate single thumbnail send input image with PUT request to URI in format:

/thumbnail/<method>,<width>,<height>,<format>[,<option key>:<option value>]*[!<edit name>[,<edit arg>]*[,<edit option>:<edit option value>]*]*

Server will respond with thumbnail data with correct Content-Type header value.

For example the URI may look like this:

/thumbnail/pad,100,100,png,background-color:green

With additional edits:

/thumbnail/pad,100,100,png,background-color:green!blur,0.2,0.1,0.6,0.6,size:0.03!rectangle,0.1,0.8,0.8,0.1,color:blue

For detailed information about the API see cucumber features.

Multipart API

To generate multiple thumbnails of single image send that image with PUT request to URI in format:

/thumbnails/<method>,<width>,<height>,<format>[,<option key>:<option value>]*[!<edit name>[,<edit arg>]*[,<edit option>:<edit option value>]*]*[/<method>,<width>,<height>,<format>[,<option key>:<option value>]*]*[!<edit name>[,<edit arg>]*[,<edit option>:<edit option value>]*]*

Server will respond with multi-part content with each part containing Content-Type header and thumbnail data corresponding to format defined in the URI.

For example the URI may look like this:

/thumbnails/crop,16,16,png/crop,4,8,jpg/pad,16,32,jpeg

With additional edits:

/thumbnails/crop,16,16,png!blur,0.2,0.1,0.6,0.6,size:0.03!rectangle,0.1,0.8,0.8,0.1,color:blue/crop,4,8,jpg/pad,16,32,jpeg!rotate,90!pixelate,0.3,0.2,0.4,0.4

HTTP Thumbnailer will generate 3 thumbnails:

  1. 16x16 cropped PNG
  2. 4x8 cropped JPEG
  3. 16x32 colour padded JPEG

For detailed information about the API see cucumber features.

Identification API

You can identify image mime type, width and height with PUT request to URI in format:

/identify

Server will respond with JSON containing contentType, width and height fields:

{"mimeType":"image/jpeg","width":1239,"height":1750}

For detailed information about the API see cucumber features.

Error status codes

HTTP Thumbnailer will respond with different status codes on different situations. If all goes well 200 OK will be returned otherwise:

400

  • requested thumbnail method is not supported
  • at least one image dimension is zero in thumbnail specification
  • missing option key or value in thumbnail specification
  • missing argument in in thumbnail specification
  • bad argument value

413

  • request body is too long
  • input image is too big to fit in memory
  • memory or pixel cache limit has been exceeded

415

  • unsupported media type - see Supported formats section

500

  • unexpected error has occurred - see the log file

Error handling with multipart API

With multipart API when error relates to single thumbnail Content-Type: plain/text header will be used for that part. In addition Status header will be set for failing part with number corresponding to above status codes. The body will contain description of the error.

Statistics API

HTTP Thumbnailer comes with statistics API that shows various runtime collected statistics. It is set up under /stats URI. You can also request single stat with /stats/<stat name> request.

Example:

$ curl 127.0.0.1:3100/stats
workers: 5
total_requests: 18239789
total_errors: 903
calling: 1
writing: 0
total_images_loaded: 17633702
total_images_reloaded: 0
total_images_downscaled: 21805
total_thumbnails_created: 17633090
images_loaded: 0
max_images_loaded: 101
max_images_loaded_worker: 101
total_images_created: 50178054
total_images_destroyed: 50178054
total_images_created_from_blob: 17634825
total_images_created_initialize: 9763067
total_images_created_resize: 16261541
total_images_created_crop: 6496816
total_images_created_sample: 21805
total_write_multipart: 0
total_write: 18238885
total_write_part: 0
total_write_error: 903
total_write_error_part: 0

$ curl 127.0.0.1:3100/stats/total_thumbnails_created
17633106

Memory limits

Each worker uses ImageMagick memory usage limit feature. By default it will use up to 128MiB of RAM and up to 1GiB of disk backed virtual memory. To change this defaults use --limit-memory option for RAM limit and --limit-disk to control file backed memory mapping limit in MiB.

Plugins

Custom thumbnailing methods and edits can be programed using plugin API. By default HTTP Thumbnailer will look for plugins in /usr/share/httpthumbnailer/plugins. Options --plugins can be used to point to different directory; it can also be specified multiple times to point to more than one directory. Plugin file needs to end with .rb extension to be found anywhere within directory structure pointed by --plugins option (or in default directory).

Defining new thumbnailing methods

To define new thumbnailing method provide block like this:

thumbnailing_method('method_name') do |image, width, height, options|
	# do something with image
end

Name of the method is defined by value of thumbnailing_method method argument (string).

Server will pass following objects:

  • image - RMagick::Image object
  • width and height - integers representing required width and height of the thumbnail
  • options - key-value map, where keys and values are strings, passed to request specification

Block should return (last value or with next keyword) new image or the image passed with image argument or nil if no change was done.

Defining new edits

To define new edit provide block like this:

edit('edit_name') do |image, arg1, arg2, argN, options, thumbnail_spec|
	# do something with image
end

Name of the edit is defined by value of edit method argument (string).

Server will pass following objects:

  • image - RMagick::Image object; input image or output of previous edit
  • all arguments as passed to the API; you can capture as many as you need
  • options - key-value map, where keys and values are strings, passed to request with edit specification
  • thumbnail_spec - object representing thumbnailing specification; you can call following methods:
    • method - name of the thumbnailing method
    • width and height - integers representing required width and height of the thumbnail
    • format - requested output format (e.g. png or jpeg)
    • options - key-value map of thumbnailing options
    • edits - array representing all edits; each edit has following methods:
      • name - name of the edit
      • args - array of edit arguments
      • options - key-value map of edit options

Block should return (last value or with next keyword) new image or the image passed with image argument or nil if no change was done.

Processing images

If more than one image is created during processing it is important to call get on every newly created image (unless it is the one being returned). This method will pass the image to first block argument and will ensure that image is destroyed after use or on exception. Returning nil or same image as input will make get to return the input image without destroying it.

Example of get usage:

	image.crop(cut_x * image.columns, cut_y * image.rows, cut_w * image.columns, cut_h * image.rows, true).get do |image|
		image.resize_to_fit(width, height) if image.columns != width or image.rows != height
	end

For examples see built-in thumbnailing methods and edits defined in built_in_plugins.rb.

Helper functions

Following helper functions are available in plugin context:

  • int!(name, arg, default = nil) - returns integer from given arg string; name is used for reporting errors; if arg is an empty string returns default if not nil or fail with 400 Bad Request
  • uint!(name, arg, default = nil) - returns positive integer from given arg string; name is used for reporting errors; if arg is an empty string returns default if not nil or fail with 400 Bad Request
  • float!(name, arg, default = nil) - returns float from given arg string; name is used for reporting errors; if arg is an empty string returns default if not nil or fail with 400 Bad Request
  • ufloat!(name, arg, default = nil) - returns positive float from given arg string; name is used for reporting errors; if arg is an empty string returns default if not nil or fail with 400 Bad Request
  • offset_to_center(x, y, w, h) - returns center ([x, y]) of the given region
  • center_to_offset(center_x, center_y, w, h) - returns offset ([x, y]) of given region center (center_x, center_y) and width and height
  • normalize_region(x, y, width, height) - returns normalized relative (values between 0.0 and 1.0) region offset and dimensions ([x, y, width, height]) that fits within normal values so that width and height will never be 0.0 (Float::EPSILON instead), x + width and y + height will never be grater than 1.0 and all values will not be negative

Additional RMagick::Image object methods are provided:

  • RMagick::Image.new_8bit(width, height, background_color = 'none') - create new image of given dimensions and background color (which can be described by pallet color name like black of by hex value)
  • render_on_background(background_color, width = nil, height = nil, float_x = 0.5, float_y = 0.5) - overlay current image on top of new image (with optionally different dimensions and floating) of given color
  • float_to_offset(float_width, float_height, float_x = 0.5, float_y = 0.5) - calculated offset ([x, y]) of image with given dimensions (float_width, float_height) on top of this image given float_x and float_y values
  • pixelate_region(x, y, w, h, size) - pixelate region given with offset (x, y) and dimensions (w, h) in pixels of pixel diagonal size (size) also in pixels
  • blur_region(x, y, w, h, radius, sigma) - blur region given with offset (x, y) and dimensions (w, h) in pixels using effect radius and sigma in pixels
  • render_rectangle(x, y, w, h, color) - draw rectangle given with offset (x, y) and dimensions (w, h) in pixels
  • with_background_color(color, &block) - do RMagick image operation that uses background color in given block and restore previous background color when finished
  • rel_to_px_pos(x, y) - convert relative offset to offset represented in pixels (using Float#floor value)
  • rel_to_px_dim(width, height) - convert relative width and height to width and height in pixels (using Float#ceil value)
  • rel_to_diagonal(v) - convert relative diagonal to diagonal in pixels (using Float#ceil value)
  • width - alias for #columns
  • height - alias for #height
  • diagonal - calculate diagonal in pixels (using Float#ceil value)

Memory usage and leaks

To avoid memory leaks (leaked images) make use of get method on intermediate images. Observe value of total_images_reloaded - if it is increasing and not dropping to 0 after you used the thumbnailing API you have a leak!

$ curl 127.0.0.1:3100/stats/images_loaded
0

Also avoid keeping too many images loaded at the same time. Chain get calls rather than nest them:

	image.get do |image|
		# image is the input image
		# image processing step 1
	end.get do |image|
		# image is now result of step 1
		# image processing step 2
	end.get do |image|
		# image is now result of step 2
		# image processing final step
	end

See also

HTTP Image Store service is configurable image storage and processing HTTP API server that uses this service as thumbnailing backend.

Known Issues

  • When 413 error is reported due to memory limit exhaustion the disk offloading won't work any more and only requests that can fit in the memory can be processed without getting 413 - this is due to a bug in ImageMagick v6.8.6-8 (2013-08-06 6.8.6-8) or less; recommended version is 6.8.7-8
  • Mime type generated for images may not be the official mime type assigned for given format; please let me know of any inconsistencies or send a patch to get better output in efficient way
  • CMYK profile JPEGs may render negative

TODO

  • Save input image data for images that has failed processing to allow further investigation
  • Allow for specifying different quality values for different image types, e.g.: quality[jpeg]:97,quality[png]:85

Contributing to HTTP Thumbnailer

  • Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
  • Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
  • Fork the project
  • Start a feature/bugfix branch
  • Commit and push until you are happy with your contribution
  • Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
  • Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

Copyright

Copyright (c) 2013 - 2015 Jakub Pastuszek. See LICENSE.txt for further details.