Label Auto-Resizer & Printer (DHL/Amazon Return Labels)

This Python tool enables automatic detection, cropping, resizing, and printing of shipping labels (currently DHL/Amazon) directly from documents received via a virtual printer (IPPServer). It is optimized for German DHL and amazon return labels with consistent layouts.

This version uses line detection instead of fixed values. Furthermore it allows you to print documents with multiple pages.

Features

• Automatic detection of DHL/Amazon labels using line detection and simple geometric features
• Dual printer support – one for labels, one for additional documents (e.g., A4 filing)
• Temporary file handling No residual files on disk
• CUPS integration for printer management, therefore not directly usable on windows systems
• Ghostscript-based conversion from PostScript to PNG

Configuration (config.ini)

[General] Section

Parameter	Default	Description
print_documents	False	Whether to print additional document info

Printer Sections

-->Name convention: Section has to start with the keyword "Printer", the rest of the name doesn't mater, because the program only uses it's types

Section	Parameter	Example	Description
[Printer_Label]	name	_PM_241	CUPS Name of my label printer
	print_format	Custom.4x6in	Print format for label printer
	type	label	Must be label for labels
[Printer_A4]	name	Samsung_ML_2160	Name of my document printer
	print_format	A4	Print format for document printer
	type	document	Must be document for documents

How It Works

1. PostScript Input:
   The IPPServer receives a print job as a PostScript file from any application.

2. Conversion:
   The script converts the PostScript file to PNG images (one per page) using Ghostscript, storing them as temporary files.

3. Label Type Detection:
   Each page image is analyzed to determine if it is a DHL or Amazon label, based on simple geometric features (e.g., a horizontal cut line for DHL).

4. Cropping and Extraction:
   The script extracts the label and (if present) the additional document section from each page, using logic defined in the code and parameters from the config. Currently document info is only extracted for DHL labels. AMZ labels are kind of tricky, because some offer additional info, others don't.

5. Printing:

   • The label section is always sent to a printer defined as label type.
   • If print_documents = True in [General] and a document section was extracted, it is sent to a printer of type document.

6. Cleanup:
   All intermediate files are handled as temporary files and deleted after use.

Requirements

• Python 3.7+
• IPPServer (for virtual print jobs)
• Ghostscript (for PS to PNG conversion)
• OpenCV (pip install opencv-python)
• pycups (pip install pycups)
• configparser (part of Python standard library)
• CUPS (Common UNIX Printing System) (pre-installed on macOS and most Linux distributions)

Installation

1. Clone IPPServer and place your Python script in the main folder.
2. Install dependencies pip install -r requirements.txt

How to run the program

Start the IPPServer and configure it to use the Python script as the print backend: python -m ippserver --port 1234 run ./LabelPrinter.py