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ImageMagick Media Filters

Overview

The ImageMagick Media Filters provide consistent, high quality thumbnails for image bitstreams, PDF bitstreams and PDF video (MP4) bitstreams.

These filters require a separate software installation of the conversion utilities (ImageMagick and Ghostscript: ImageMagick, Ghostscript (to support PDF thumbnails) and/or ffmpeg (to support MP4 thumbnails).  

The media filters use the library im4java to invoke the conversion utilities.  This library constructs a conversion command launches a sub-process to perform the generation of media files.

Installation

Before ImageMagick Media Filters can be used, you must setup ImageMagick (and optionally Ghostscript) as follows:

1. Install ImageMagick

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1. on your server.  The installation process differs based on your operating system.  For example, on Debian/Ubuntu, it's similar to this:

   Code Block
   apt-get install imagemagick

   
   

2. If you wish to generate PDF thumbnails, install Ghostscript

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1. on your server. The installation process differs based on your operating system.  For example, on Debian/Ubuntu, it's similar to this:

   Code Block
   apt-get install ghostscript

   
   

2. (New in 7.6) If you wish to generate MP4 (video) thumbnails, install FFmpeg on your server. The installation process differs based on your operating system.  For example, on Debian/Ubuntu, it's similar to this:

   Code Block
   apt-get install ffmpeg

   
   

3. The ImageMagick, Ghostscript, and FFmpeg

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1. executables should be accessible from the same directory (e.g. /usr/bin)
   1. This directory MUST be defined in the org.dspace.app.mediafilter.ImageMagickThumbnailFilter.ProcessStarter configuration as describe below.

DSpace Configuration

In the filter.plugins section of your dspace.cfg (or local.cfg file) file, uncomment specify the ImageMagick media filter definitionfilters you wish to use.

# Make sure to always keep this plugin enabled if you want to support search within text documents
filter.plugin = Text Extractor

# NOTE: When "ImageMagick Image Thumbnail" is enabled, the default "JPEG Thumbnail" should NOT be enabled
filter.plugins = ImageMagick Image Thumbnail

# NOTE: When "ImageMagick PDF Thumbnail" is enabled, the default "PDFBox JPEG Thumbnail" should NOT be enabled
# Requires Ghostscript to also be installed
filter.plugins = ImageMagick PDF Thumbnail

# New in 7.6, \ this will generate thumbnails from video files.
# Requires ffmpeg to also be installed
filter.plugins = ImageMagick Video Thumbnail   

This will activate the following settings which are already present in dspace.cfg :(these do NOT need to be added, as they already exist)

   plugin.named.org.dspace.app.mediafilter.FormatFilter = org.dspace.app.mediafilter.ImageMagickImageThumbnailFilter = ImageMagick Image Thumbnail, \
   
plugin.named.org.dspace.app.mediafilter.FormatFilter = org.dspace.app.mediafilter.ImageMagickPdfThumbnailFilter = ImageMagick PDF Thumbnail
plugin.named.org.dspace.app.mediafilter.FormatFilter = org.dspace.app.mediafilter.ImageMagickPdfThumbnailFilterImageMagickVideoThumbnailFilter = ImageMagick PDFVideo Thumbnail

These media filters contain the several properties which can be configured.

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The following property provides a path to the ImageMagick and GhostScript (convert), GhostScript (ghostscript), and ffmpeg utilities.

org.dspace.app.mediafilter.ImageMagickThumbnailFilter.ProcessStarter = /usr/bin

Supported file formats

Each of these ImageMagick filters has its own list of configurable file formats.  The defaults are usually best, but may be updated if you have custom bitstream formats.  These settings already exist in your dspace.cfg.

filter.org.dspace.app.mediafilter.ImageMagickImageThumbnailFilter.inputFormats = BMP, GIF, PNG, JPG, TIFF, JPEG, JPEG 2000
filter.org.dspace.app.mediafilter.ImageMagickPdfThumbnailFilter.inputFormats = Adobe PDF
filter.org.dspace.app.mediafilter.ImageMagickVideoThumbnailFilter.inputFormats = Video MP4

Overwriting Existing Thumbnails

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PDFs optimized for physical printing often use the CMYK color space. On the web, however, the de facto color system is sRGB. By default, DSpace's ImageMagick-based thumbnailing system will create thumbnails that use the same color space as the source PDF. Most web browsers are not able to correctly display images that use the CMYK color space, which leads to images with visibly inaccurate colors. Furthermore, the JSPUI currently does not support the display of thumbnails that use the CMYK color space (see DS-2834). 

If you are using Ghostscript version 9 or above, it is possible for DSpace to correctly convert images from CMYK to sRGB by providing it with appropriate ICC color profiles to use during thumbnail creation. Default ones are provided by most Ghostscript installations (version 9 or above). The following configuration options tell DSpace where those ICC profiles are located.

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Providing ICC profiles to ImageMagick is optional. If these configuration properties are unset, no profiles will be supplied to ImageMagick, and thumbnails produced from PDFs using the CMYK color space will also use CMYK. The transformation from CMYK to RGB is optional, but keep in mind that thumbnails using CMYK will cause problems if you use JSPUI and display thumbnails on browse and search pages (see DS-2834).

Override ImageMagick Default Density

It is possible to override ImageMagick's default density of 72 DPI when creating PDF thumbnails. This increases the quality of resulting thumbnails at the expense of slightly longer execution times and higher memory usage. Any integer over 72 will help, but recommend 144 for a "2x" supersample. See the following configuration option in dspace.cfg :

# org.dspace.app.mediafilter.ImageMagickThumbnailFilter.density = 144

The effect is most notable on PDFs with a lot of text, gradients, or curved lines. See the pull request implementing this feature for more information and comparisons.

Additional Customization

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Note: The PDF thumbnail generator is hard-coded to generate a thumbnail from the first page of the PDF.

Possible Errors / Issues

"convert.im6: not authorized" errors

On Ubuntu (possibly other OSes), you may see errors like these when attempting to generate PDF thumbnails:

ERROR filtering, skipping bitstream:
        Item Handle: 1234/5678
        Bundle Name: ORIGINAL
        File Size: 30406135
        Checksum: c1df4b3a4755e9bed956383b61fc5042 (MD5)
        Asset Store: 0
org.im4java.core.CommandException: org.im4java.core.CommandException: convert.im6: not authorized `/tmp/impdfthumb6294641076817830415.pdf' @ error/constitute.c/ReadImage/454.

OR
 
org.im4java.core.CommandException: convert-im6.q16: attempt to perform an operation not allowed by the security policy 'PDF' @ error/constitute.c/IsCoderAuthorized/421

These may be caused by a change in your ImageMagick policy configuration on your server. 

In Ubuntu, the default "policy.xml" was recently updated to exclude all Ghostscript formats (including PDF, PS, etc).  See this ticket: https://bugs.launchpad.net/ubuntu/+source/imagemagick/+bug/1796563

• This exclusion was implemented to workaround a security vulnerability in Ghostscript reported here: https://www.kb.cert.org/vuls/id/332928
• According to that vulnerability report, this was patched in Ghostscript v9.24 (or above)

The newly added lines in the /etc/ImageMagick/policy.xml are these ones:

<!-- disable ghostscript format types -->
<policy domain="coder" rights="none" pattern="PS" />
<policy domain="coder" rights="none" pattern="EPS" />
<policy domain="coder" rights="none" pattern="PDF" />
<policy domain="coder" rights="none" pattern="XPS" />

To fix the error above requires you to re-enable ImageMagick to process Ghostscript format types. That can be done by simply commenting out those new "policy" lines in the configuration file (surround them with <!-- and --> to comment out)

Be aware that you MUST ensure you are running Ghostscript v9.24 or later to ensure that you are not at risk for the above security vulnerability in older versions of Ghostscript.

"convert-im6.q16: cache resources exhausted" errors

On Debian, and possibly other OSes, you may see errors like these when attempting to generate video thumbnails (especially if video files are big):

File: video.mp4.jpg
ERROR filtering, skipping bitstream:
        Item Handle: 1234/5678
        Bundle Name: ORIGINAL
        File Size: 146761357
        Checksum: 735ceb1b6b249afc84a5bb1b87ae0c02 (MD5)
        Asset Store: 0
org.im4java.core.CommandException: convert-im6.q16: cache resources exhausted `/tmp/magick-64dziU-1nQJjQHZYu4_R1fFP4l9en5iL.pam' @ error/cache.c/OpenPixelCache/4095.

These may be caused by too conservative resource policies in your policy.xml file. As an example, default values are located at /etc/ImageMagick-6/policiy.xml in Debian 11 (Bullseye), and are:

<policymap>
  <!-- <policy domain="resource" name="temporary-path" value="/tmp"/> -->
  <policy domain="resource" name="memory" value="256MiB"/>
  <policy domain="resource" name="map" value="512MiB"/>
  <policy domain="resource" name="width" value="16KP"/>
  <policy domain="resource" name="height" value="16KP"/>
  <!-- <policy domain="resource" name="list-length" value="128"/> -->
  <policy domain="resource" name="area" value="128MP"/>
  <policy domain="resource" name="disk" value="1GiB"/>

To avoid the cache resources exhausted error, try increasing the resource limits policies. You may want to start by increasing the memory and disk policies (disk cache is used when the memory limit is reached). The actual values have to be adjusted depending on the size of your video bitstreams and the actual resources available in your installation. For example:

<policymap>
  <!-- <policy domain="resource" name="temporary-path" value="/tmp"/> -->
  <policy domain="resource" name="memory" value="4GiB"/> <!-- memory limit increased from 256MiB to 4GiB -->
  <policy domain="resource" name="map" value="512MiB"/>
  <policy domain="resource" name="width" value="16KP"/>
  <policy domain="resource" name="height" value="16KP"/>
  <!-- <policy domain="resource" name="list-length" value="128"/> -->
  <policy domain="resource" name="area" value="128MP"/>
  <policy domain="resource" name="disk" value="4GiB"/> <!-- disk limit increased from 1GiB to 4GiB -->

For a detailed description of the ImageMagick limits, see https://imagemagick.org/script/command-line-options.php#limit.

Once the limits are properly set, a successful execution of the filter should show a message similar to:

File: video.mp4.jpg
FILTERED: bitstream 12345678-abcd-efgh-ijkl-1234567890ab (item: 1234/5678) and created 'video.mp4.jpg'