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Couchmagick

Run ImageMagicks convert on CouchDB documents.

Couchmagick runs as an os_daemon, which means that CouchDB manages the process and you can configure it using CouchDBs configuration mechanism, which is both a huge win.

Versions and commandline arguments which are passed to convert are defined in design documents under a couchmagick section.

Couchmagicks couch-daemon stream based implementation provides low memory footprint.

Installation

The installation of Couchmagick is dead simple.

Make sure you have ImageMagick installed, eg on Debian:
apt-get install imagemagick

Install Couchmagick via npm:
npm install couchmagick -g

Commandline Client

You can run Couchmagick from the commandline:

couchmagick

The options explained above can be given as commandline parameters (prefixed with --) or environment variables (UPPERCASED).

couchmagick --username bernd --password secure --whitelist projects --concurrency 8 --timeout 1000

Daemon Configuration

Add Couchmagick to os_daemons config section (eg. in local.ini):

[os_daemons]
couchmagick = couchmagick

Now CouchDB takes care of the Couchmagick process.

[couchmagick]
; Optional username and password, used by the workers to access the database.
; Default is null.
username = bernd
password = secure
; Concurrency level (number of simultanous convert processes per stream). Default is 1.
; this should be set to the number of cores of your cpu for optimum performance, but
; it really depends on the number of databases and their usage patterns.
concurrency = 1
; Timeout for a convert process in ms. Default is 60000 (1min). This should be plenty
; for the usual image resizes, increase it if you deal with really large images and complex
; imagemagick processing.
timeout = 60000
; Only documents in the databases below are processed (separate with comma).
; Regular expressions are allowed:
;whitelist = mydb,otherdb,/^special-.*/
; Ignore the following databases (again comma separated list)
; Regular expressions are again allowed:
blacklist = /^_/
; Only attachments which match any of the mime types below are processed (separate with comma).
; Default is /^image\// Regular expressions are allowed:
;source_content_types = /^image\//,application/postscript

Imagemagick Configuration

Add a couchmagick property to a design document. Couchmagick will process all databases which have such a design document.

Minimal Example

{
  "_id": "_design/minimal-couchmagick-config",
  "_rev": "1-a653b27246b01cf9204fa9f5dee7cc64",
  "couchmagick": {
    "versions": {
      "thumbnail": {
        "args": [
          "-resize", "x100"
        ]
      }
    }
  }
}

`filter`

There are two kinds of filters which you can define: one operates on doc level and one on version level.

Document Filter

This filter is called with one argument: document.

Version Filter

This filter is called with two arguments, document and attachment name.

`content_type`

Content-Type of the resulting attachment. Default is image/jpeg.

`id`

The document id where the version is stored. Defaults to {id}/{version}.

Can have the following strformat placeholders:

id - the original doc id
parts - array of the id splitted at /
docuri - docuri parsed id object:
docuri.type - index part of docuri
docuri.id - id part of docuri
docuri.subtype - subtype part of docuri
docuri.version - version part of docuri
docuri.index - index part of docuri
version - name of the version

`name`

The attachment name of the version. Default is {basename}-{version}{extname}.

Can have placeholders:

id - the original doc id
parts - array of the id splitted at /
docuri - docuri parsed id object:
docuri.type - index part of docuri
docuri.id - id part of docuri
docuri.subtype - subtype part of docuri
docuri.version - version part of docuri
docuri.index - index part of docuri
version - name of the version
name - original attachment name, eg this/is/my-image.jpg
extname - file extenstion of the original attachment name, eg .jpg
basename - basename without extension, eg my-image
dirname - directory name, eg this/is
version - name of the version

`args`

Array of argument strings for ImageMagicks convert.

The default is ['-', 'jpg:-'], which means that ImageMagick converts the image to jpg. You can see that we use convert with pipes for in- and output.

See ImageMagick Convert Command-line Tool for a comprehensive list of options.

Advanced Example

{
  "_id": "_design/advanced-couchmagick-config",
  "_rev": "1-0b42e71d7b179c7e44a436704e4fd8e3",
  "couchmagick": {
    "filter": "function(doc) { return doc.type === 'post'; }",
    "versions": {
      "medium": {
        "id": "{id}-{version}",
        "name": "{basename}/{version}{extname}",
        "args": [
          "-resize", "800x600",
          "-quality", "75",
          "-colorspace", "sRGB",
          "-strip"
        ]
      },
      "large": {
        "filter": "function(doc, name) { return name.match(/^header/); }",
        "id": "{id}-header",
        "name": "header/large.jpg",
        "args": [
          "-quality", "75",
          "-unsharp", "0",
          "-colorspace", "sRGB",
          "-interlace", "Plane",
          "-strip",
          "-density", "72",
          "-resize", "960x320^",
          "-gravity", "center",
          "-crop", "960x320+0+0", "+repage"
        ]
      }
    }
  }
}

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