Introduction
Components
Requirements
APPENDIX A. Requirement specification for image output from a reading device
Retrieving digital data from film requires two processes. The first process is the image capturing from the film and the second is the decoding of that captured image file. This document covers the first process: the capturing. This document describes the minimum optical parameters required for building an image capturing device optimize for digital data exposed on 35 mm film. The document does not describe the film transport mechanism as this is implemented according to the image capturing device requirements.
There are three main components to capture an image from the film; the sensor, the optics, and the light source. Also, the film needs to be advanced frame by frame or continuously, either manually or through a motorized transport system.
Image capturing device (Film scanner) The capturing device converts a photographic image into an array of 8-bit values in the physical memory. Each element if this array represents a specific area on film. The size of this area is the size of the printed pixel (6,08 microns) divided by the oversampling factor. At the time of creation of this document, the film content was captured using a Eliixa e2v line sensor, continuously capturing lines while the film was moving past the sensor. The total number of captured pixels per recorded image was: 12288 x 6879. However, the image can be captured by a digital camera with a CMOS or CCD sensors. See in Appendix A, the requirement specifications for image output from a reading device.
Oversampling more than x2.8 is recommended to achieve sufficient image quality for data restoration. The film frames are exposed using a 4K image device, so the minimum recommended sensor size is 11,2K
The frame's dimension on the film is 24,92 mm width by 13.87 ± 0.05 mm height (Defined in SMPTE-59) (1) The lens shall allow to capture the entire printed frame with approximately 200 μm margins*.* The pixel size in the frame is 6,08 μm x 6,08 μm, Modulation Transfer Function (MTF) describes the lens performance by measuring the transfer of modulation (or contrast) from the film to the image sensor When choosing the lenses together with the image sensor, the MTF should be higher than 75% at 83 lp/mm.