1. Introduction
2. Technology
2.1. Security, integrity and authenticity 2.2. Retrieval process
3. How to retrieve data from this film?
3.1. Read the Representation Information 3.2. Build the decoding software 3.3. Capture frame images 3.4. Decode frames 3.5. File format specifications / file readers
At the end of the 20th century, users of digital storage technologies faced a difficult challenge due to the exponential growth of data produced, the vulnerability of the storage mediums and the ever-changing application software. This challenge forced users to implement strategies for data preservation based on complicated software and hardware migrations. These strategies proved to be expensive and risky, but there were the only available options at the time. Piql answered to this challenge creating a holistic data preservation solution where data integrity and authenticity was preserved using a solid medium with a well-documented lifetime and implementing features which allow users in the future to recreate the reading technology using the information written on the medium.
The solution foundation was a technology based on storing digital data on a photosensitive polyester film creating an ultra-secure, migration-free, long-term preservation solution for digital data. This digital preservation medium is designed to last over 500 years and allows to interpret the data despite software obsolescence. Piql combined the longevity of the polymers and silver halides with the ability to store the instructions on how to decode the information stored on the film in human readable format. This document describes briefly the data preservation technology, the steps taken to ensure the authenticity of the data, and dives into the process to retrieve the content from the film.
Piql’s technology uses an optical recording medium for digital storage. This medium is a 35mm width polyester film coated on one side with a gelatine emulsion containing microscopically small light-sensitive silver halide crystals. The silver halides are darkening when exposed to light, and Piql used this characteristic to expose binary data in frames along the film. Both components of the film, polyester, and silver are extremely stable, and they are proved to last over 500 years when stored properly (film environmental storage recommendations are 21 Celsius and 50% Relative Humidity).
The software technology used to decode the data is open source, freely available and was tested using several operating systems. The hardware technology to capture data from the film is widely available, and the only requirement is an image capturing device able to sample images as a 2D array of color intensity values.
There are three hardware components at the core of the solution. The piqlWriter, a machine using photons to transfer data onto the film medium. The piqlProcessor, a machine where the written information on the film is chemically fixed. The latent silver halide particles exposed to light are converted into metallic silver and fixed to ensure image permanence. The piqlReader, a machine reading frames from the film and converting them into sampled images which are decoded back to digital data.
For retrieving the data from a film, the only component needed is the piqlReader. However, the piqlWriter has been playing a bit part in the preservation process providing integrity and authenticity to the data.
They are several technology elements in the piqlWriter. The core technology element that provides data reliability on film is the imaging technology. The imaging is based on a Texas Instruments1 Digital Lightning Processing (DLP) imaging sensor with 4K resolution (4096 x 2160 pixels), consisting on more than 8’800,000 micro-mirrors able to write pixels of 6μm size. The piqlWriter uses a monochromatic green LED light which is modulated by the DLP. The DLP micromirrors tilt either toward the light source (ON) or away from it (OFF) creating a light or dark pixel on the projected film surface.
For Piql’s digital application, every pixel represented a binary data container. This exposing technology allows writing pixels with excellent contrast allowing to achieve high data density per frame. In this was, it is possible to reproduce the binary stream of the client digital content. After exposing the film, the pixels’ value cannot be changed, providing a true WORM (Write Once Read Many) storage medium. The Imaging technology, combined with the software and the production processes makes the data content in this film secured, integral and reliable.
Piql makes sure clients’ valuable digital data is safe and accessible, irrespective of future financial capabilities and technological developments. Piql Preservation Services uses an OAIS2 compliant turnkey solution to provide clients with a secure, accessible and migration-free solution for digital preservation. The OAIS reference model provides the guidelines for creating a Piql digital repository. This repository must fulfill the criteria for which clients entrust their data to Piql technology. These criteria are data security, integrity, authenticity, and reliability. Data security was ensured during the entire preservation process, from ingestion to physical storage. When transferring data, mechanisms for secure data transfer are applied. There are secure online data transfer protocols and secure physical transport services. The online transfer protocols used are HTTP over SSL, SSH FTP, and secure VPN tunnels. The advantage of these protocols is the ability to leverage a secure connection to transfer files. The Piql system was configured to work in a closed network environment. The receiving data server in Piql was in the Demilitarized Zone (DMZ) protected by firewalls with restricted access ports.
Only one trusted person had access to client files and is responsible to ingesting the files into the Piql system. The physical transfer service was provided on a ruggedized and shockproof hard drive with 256-bit encryption support with USB interface. The client entrusted one person to unencrypt the hard drive when arriving at Piql
Independent of the transfer method, the client had the option to encrypt the data content. The content could be preserved on film encrypted or unencrypted. The client always has control over the data.