Principal maintainer of GraphicsMagick. Author of Magick++ (C++ API to ImageMagick and GraphicsMagick). Author of module loader facility, automatic file identification (magic) support, Unix/Cygwin/MinGW configure/make facility, Windows setup.exe style installer, WMF renderer, C API documentation formatter, and the C, C++, and Perl test suites used by ImageMagick and GraphicsMagick.

Authored the ART, CUT, HRZ, JNX, MAC, MATLAB, TOPOL, and WPG coder modules. Improved the FITS and TXT coder modules. VisualMagick 'configure' improvements and build testing/fixes for many versions of Microsoft Visual Studio.

Authored the HEIF and JPEG XL coder modules.

Contributed significantly to the utilities, including writing the 'gm' utility wrapper. Authored support for JNG, MNG, and PNG formats. Provided significant support for the BMP format. Significant improvements to the documentation, including creating a documentation authoring environment based on the <imdoc> format. Maintained the SourceForge mailing lists. GraphicsMagick would not be what it is today without Glenn and he will always be remembered.

Contributed significant improvements to the SVG parsing and rendering code.

Contributed a several significant patches to fix image rotation bugs and improve image rotation performance, as well as an improved bi-linear interpolation implementation.

Contributed the implementation of 'gm batch', a simple batch mode for GraphicsMagick.

Contributed a number of Wand API functions as well as fixes for several composition operators.

Contributed a large number of new Photoshop composition operators and alpha-channel fixes for existing ones.

Contributed improvements to the VisualMagick configure program to support configuring more build options via the GUI dialogs and to deal with similarly named files.

Contributed WebP coder improvements.

Created and maintains the Borland C++ Builder 6.0 build environment for GraphicsMagick.

Provided many security patches and fixes from the Debian project.

Author of the VisualMagick project configure facility for Visual C++. Author of FlashPix module. Author of the ImageMagickObject COM object for Windows. Author of the EMF, XTRN, and META coders. Significant contributions to the MSL, JPEG, TIFF, SVG, and URL coders. Authored "process" module support. Wrote the micro-timer facility used by 'identify'. Ported module loader support to Windows. Significantly improved polygon rendering performance.

Authored the 'conjure' utility and associated MSL execution environment. Provided MacOS support. Authored the CLIPBOARD, XCF, and PSD coders. Postscript and PDF expertise. Significant drawing enhancements including support for dash patterns, linecap stroking, clipping masks and a mask image.

Contributed the -clippath functionality, added -define support, improved color profile support, and re-wrote the PS3 coder.

Principal author of TclMagick.

Co-author of TclMagick, particularly in the Unix environment.

Contributed a new design for the web pages, including the formatting scripts, and converted many pages to the new format.

Contributed code for converting between native floating point types, and short (16/24) bit float types.

Contributed Hald CLUT and ASC-CDL implementations.

Re-wrote the HP PCL writer to work much better, including support for compression. Implemented support for CALS type 1 format. Re-wrote the DICOM reader.

Contributed the adaptive threshold implementation (-lat), which executes in linear rather than quadratic time.

Contributed support for the Braille image format.

Creator, principal author, and principal maintainer of ImageMagick, from which GraphicsMagick is originally derived (from ImageMagick 5.5.2). Also the author of the Wand API to ImageMagick which is incorporated as a stand-alone library by GraphicsMagick.

Authored the initial Cineon coder (which has since been replaced).

Authored the PALM coder.

Ported the WMF coder to the libwmf 0.2 API.

Contributed code to support filling drawn objects using a pattern image.

Original author of the JP2 coder.

Original author of PerlMagick. Original author of the LOCALE coder.

Original author of Base64 encode/decode sources.

Contributed (with Leonard Rosenthol) dash pattern, linecap stroking algorithm, and minor rendering improvements.

Authored the source RPM spec file for GraphicsMagick.

Contributed support for Wireless BitMap, used in WAP - Wireless Access Protocol.

Contributed the median filter algorithm.