Goblin Converter

A simple document converter GUI for GTK using magick

Initial use case was to convert 300ppi (PDF) documents (grayscale or colored) to monochrome (PDF) documents to reduce the size significantly for digital document storage.

E.g. a PDF document with 300ppi and about 3-4MB in grayscale can be reduced to about 40-75KB(!) in monochrome.

- Warning: This app is in early development and may not work as expected or at all due some refactorings.

Setup

This app is distributed as a Flatpak package or can be installed locally.

Flatpak

# Not available yet, follow the Local installation guide
flatpak install flathub de.magynhard.GoblinConverter

Local

Ensure, Crystal is installed.

Beside, you need to have build tools and other dependencies to be installed.

Ubuntu

sudo apt install build-essential libcairo2-dev libgirepository1.0-dev libgdk-pixbuf2.0-dev libgtk-4-common libgtk-4-dev libadwaita-1-0 libadwaita-1-dev imagemagick crystal

Manjaro/Arch

sudo pacman -S base-devel crystal gtk4 libadwaita imagemagick

Install

git clone https://github.com/magynhard/goblin-converter.cr.git
cd goblin-converter.cr
shards install
make install

Uninstall

cd goblin-converter.cr
make uninstall

Development

Target platforms are Linux (primary) and Windows. macOS is not planned.

Requirements (development)

• Crystal 1.21+
• GTK4
• ImageMagick 7
• Ghostscript 10

Windows (verified 2026-10-02, MSVC route)

Build must run on a Windows machine (no cross-compile from Linux):

1. Install: Crystal for Windows (MSVC, portable zip) + VS2022 Build Tools ("Desktop development with C++", MSVC v143 x64) + Windows 10 SDK. Enable Developer Mode in Windows Settings.
2. Unzip a wingtk/gvsbuild GTK4_Gvsbuild_<ver>_x64.zip to C:\gtk (provides GTK4/Adwaita, GObject-Introspection, pkg-config, msgfmt).
3. Per PowerShell session, load the env (adjust paths if needed):

   . .\scripts\goblin-env.ps1 [-GtkDir C:\gtk] [-CrystalDir ...] [-ImageMagickDir ...] [-GhostscriptDir ...]
   

4. Then as usual (no make needed):

   shards install
   .\bin\gi-crystal.exe
   crystal build src/goblin-converter.cr -o bin/goblin-converter.exe
   crystal spec
   

   make install is Unix-only. Runtime needs ImageMagick 7 (magick.exe, portable zip works) and Ghostscript 10 (gs installer, run elevated — there is no portable zip) plus C:\gtk\bin on PATH (for the GTK DLLs). Tip: if monochrome Fax/PDF output looks broken and your user name contains non-ASCII chars, set MAGICK_TEMPORARY_PATH to an ASCII-only directory.

Install local for development

make install

Build

make build

Run

make run

Create locales

make locales

Clean

make clean

Create new version

Update version in shard.yml

version: 0.X.X

Create tag

git tag 0.X.X
git push origin 0.X.X