Storage medium description
This article goes in depth of describing the piqlFilm
1. Introduction
The piqlFilm storage medium is a polyester film coated with a gelatine layer of light-sensitive silver halides. The storage medium’s physical properties are the same as used in 35mm picture film and it follows all SMPTE motion picture standards. The film is exposed with light to store a latent image with digital data, the film is then developed and the latent image is permanent. The film has been used in analogue cinematography where analogue images are represented in every frame. The film’s excellent image permanence and polyester and silver stability has made it the preservation standard for analogue image preservation in the microfilm industry. Piql has seen the advantages of this medium and developed a technology where binary data is exposed on the film, taking advantage of the mechanical and longevity characteristics of the film, and extending it to the digital realm. In addition, the image permanence characteristic makes the film a true WORM (Write One Read Many) digital storage medium, meaning the digital information can safely remain unchanged.
The film now becomes a digital storage medium with same technical storage properties as current digital storage solution such as magnetic tapes, hard drives, sold state drives and optical discs, but adding the reliability, security and longevity of the medium. In addition, the possibility of exposing human readable characters on film gives the film a “self-contained” feature which allows to describe instructions needed to interpret and decode the digital content in the future.
2. Specifications
2.1. Film Structure
Film is made of layers, and it is the combination of these layers that give the characteristics of piqlFilm.
Polyester base The film base is a transparent polyester film (PET (polyethylene terephthalate)) of 100 microns thickness. The film’s high strength, chemical stability, toughness, tear resistance, flexibility and dimensional stability allows to manufacture a thin film that provides large digital storage density.
Emulsion This is a gelatine emulsion layer of 8 microns thickness containing microscopic small, light-sensitive silver-halide crystals. Emulsion is made by dissolving silver bullion in nitric acid to form silver-nitrate crystals. These crystals are dissolved and mixed with other chemicals to form silver-halide grains and then suspended in a gelatine emulsion coating. The emulsion is the data layer where the information is stored.
Surface Overcoat This is the top layer of the film. The purpose of this clear layer of hardened gelatine is to protect the emulsion from damage during handling. It provides scratch protection and more robust physical properties to the film.
Subbing layer This layer is applied to the film base so that the emulsion adheres to the base.
Antihalation backing Light penetrating the emulsion of a film can reflect from the base-emulsion interface back into the emulsion, causing a secondary exposure. The antihalation layer is a dark coating on or in the film base that will absorb and minimize this reflection. This layer has four purposes: antihalation, antistatic, lubrication and scratch protection.
2.2. Dimensions
35 mm film is the film gauge most commonly used for motion pictures and chemical still photography from the late 1800s to the present (early 21st century). The name of the gauge refers to the width of the film, which consists of a long strip 34.98 ±0.03 mm wide.
The film has 3 perforations (KS1870) per frame along both edges with the following dimensions:
The following are the frame dimensions:
Dimensions Inches Millimeters A 0,981 nom 24,92 nom B 0,546 +/- 0,002 13,87 +/- 0.05 Perforation Pitch 0,186 +/- 0,004 4,72 +/-0.1
2.3. Characteristics
A low-speed, high-contrast, black and white, negative film with extremely fine grain (20 nm to 40 nm) and high resolving power (1180 line pairs per mm). Film has been optimized for the piqlWriter’s exposing system to 520 nm wavelength. In addition, the Film has been optimised for stress, friction and conductivity to run well through piqlReader or any high-speed film scanner.
2.3.1 Sensitometry
The sensitometric curve and data in this section represent product tested under the conditions of exposure and processing specified. (D97 developer, 21oC (70oF), at 6 minutes 30 seconds). See graphic in appendix 1. piqlFilm technical specifications by Kodak.
2.3.2 Spectral sensitivity
This curve depicts the sensitivity of the piqlFilm in the spectral region of most interest. See graphic in appendix 1. piqlFilm technical specifications by Kodak.
2.4. Data storage capacity
A frame is the storage unit in the physical preservation medium. The film allows to preserve data in digital and visual mode (analogue pictures) within a frame. For the visual part, there are 70 frames per meter (39,37 in). The length of the film is 950 meters (3118 ft).
Digital preservation Capable of storing up to 2,5 bits (per pixel). Current storing capacity: 2 bits (per pixel) – 120GigaBytes per Reel
Visual preservation Exposing several visual images in one frame is flexible and it is dependent of the dots per inches (dpi) output desired. For example, exposing 12 x A4 pages per frame allows to exposed about 780,000 images per reel at 85dpi.
2.5. Core
The film is winded on a bottom plate with an integrated core. This helps to improve film handling. The core follows the ANSI/SMPTE standards for 35mm motion-picture films (except for dimension A below).
Where: • A: 37.5 mm (1,000 in) – SMPTE standard is 34,9 mm (1,374 in) • B: 75 mm (2,953 in) • C: 25,7 mm (1,012 in) • D: 29,5 mm (1.161 in) • Ε: 3,8 μμ (0,150 ιν)
Height of the piqlBox core (dimension A) is higher than the SMPTE standard, so the cover of the piqlBox can rest on the core without damaging the film.
2.6. Film Identification
The film identification or edge signing is information exposed to film during film manufacturing. It provides mechanisms for film authenticity and quality control. After processing the film, the edge signing will have the following information:
piqlFilm by Manufacture cccc eee rrrpp ss ffff yyyy
Where: • Manufacture = Company manufacturing the film • c = product code (manufacturer code) • e = emulsion (manufacturer emulsion code) • r = roll number (master roll) • p = part number (part in the master roll) • s = slit number (slit from the master roll/part, 1 to 38 from left to right) • f = footage (incremental foot numbering along the slit) • y = year (manufacturing year)
2.7. Storage conditions
The piqlFilm must be stored in a piqlBox after processing to ensure longevity and compatibility with the piqlReader. To ensure maximum longevity, storage conditions must comply with ISO standards for image permanence (ISO 18911:2010 – “Imaging materials, Processed Safety Photographic Films, Storage Practices”):
• The storage location shall maintain a relative humidity in the range 20 – 50 % and cycling of the relative humidity shall not be greater than ±5 % during any 24 h period. • The storage location shall maintain a temperature in the range of 4 – 21 °C and cycling of the temperature shall not be greater than ±2 °C during any 24 h period.