Archiving Film – Using a High-Resolution Camera to Digitally Store Film

The scanning and archiving of film is considered to be of significant importance as it aims to preserve footage for future generations.

However, traditional cellulose, acetate-based film is subject to decay because of its organic composition. The decomposition of film is accelerated by acid, moisture, and heat, and leads to warping and shrinkage of the medium. Irreversible chemical degradation, called vinegar syndrome, is caused by leaching of acetic acid from the film.

The leaching acid makes the syndrome contagious when it comes into contact with other portions of the film. The decay makes the film become very brittle; ultimately reducing it to powder.

Before this happens, it is vital to archive the footage, preferably through digital media, for preservation. A film archiving solution vendor has consulted with and selected Lumenera as their camera supplier to image and preserve film in different decay states.

Film in advanced state of decay due to vinegar syndrome

Film in advanced state of decay due to vinegar syndrome

The Ideal Camera

For a number of reasons, Lumenera’s high performance Lt16059H is considered to be the ideal camera for this application. The camera has a 16 megapixel OnSemi KAI- 16070 CCD image sensor, which has the potential to capture more than 4K resolution at an industry-leading speed of 12 frames per second (fps), with outstanding color reproduction. This speed is attained by overclocking the sensor and using its four available image taps to process the frames. This is followed by recombining the four quarter frames into one, using Lumenera’s proprietary tap-matching algorithm, resulting in seam-free images. As an industry leader, Lumenera is capable of generating complete frames without any noticeable tap seams.

Resolution Comparison: TV standards & Lt16059H

Resolution Comparison: TV standards & Lt16059H

Vendor Specific Requirements Met by Lumenera

Lumenera is capable of carrying out large-to-small customizations and can further provide an imaging solution to meet its customers’ exact application requirements. For instance, in the case of one vendor’s application, it was essential to access the unmatched tap data for their specific archival needs.

Engineers at Lumenera provided the vendor with a custom feature within their archival imaging software to access the important data. This collaboration between the vendor and Lumenera resulted in timely camera integration with the exact specifications needed for the application.

When a customer needs sharpness and color accuracy within the image scanning process, Lumenera uses the monochrome version of the OnSemi sensor, combined with a color wheel. A full color frame is produced in this method by combining three monochrome images exposed to blue, green, and red light.

Using a color wheel, the light source of steady intensity is broken into the three primary colors used in film. Traditional color image sensors break these color filters into a Bayer pattern, and these filters are applied to each pixel individually. This is followed by interpolating the two missing color channels for each pixel through a process called "demosaicing." Artifacts such as zippering and false color can be introduced into the image based on the demosaicing algorithms used.

The utilization of a monochrome image sensor and a color wheel will entirely remove these artifacts as every single pixel will be exposed to all three color channels.

Example of false coloring.

Example of false coloring. (Source: Wikipedia)

Example of zippering.

Example of zippering. (Source: Wikipedia)

Two Approaches to High Dynamic Range

A color wheel creates the opportunity of imaging with high dynamic range (HDR), even though it slows the archiving process. The film can be enhanced by capturing each frame with varying intensities of light. This results in better quality and more detailed images.

Using the Lt16059H’s General Purpose Input/Output (GPIO), the camera can trigger the flash, or be triggered by the flash with an extremely high level of determinism. The camera features a hardware trigger that facilitates synchronization with both the system and light source as a whole, as it has a delay in the order of microseconds.

The sensor’s built-in HDR mode serves as an alternative to exposing the frame multiple times and post-processing the images to create HDR frames. At the time of this publication, Lumenera stands out as the only industrial camera manufacturer who has successfully made this feature available for demonstrative purposes.

The sensor slows the frame rate to 6 fps in order to capture a single image with two varied gain levels, and outputs a single HDR frame with no post-processing required by software. When compared to the original frames, the resulting merged HDR frame has better dynamic range. This feature is being developed, and future enhancements have been planned to provide even wider dynamic range and end user customization.

Archival film scanner at Reflex Technologies.

Archival film scanner at Reflex Technologies.

The effect of high dynamic range imaging.

The effect of high dynamic range imaging. (Source: Wikimedia)

The Lt16059H – The Right Choice for Digitally Archiving Film

A bit depth of up to 14-bits per pixel is supported by both the monochrome and color variants of the Lt16059H camera, capturing the high degree of variance in light that is essential for archiving. The large data payload generated by the Lt16059H is combined with the high resolution and frame rate of the camera, and transferred by a USB 3.0 interface with speeds of up to 5 Gbps. Lumenera is presently the only provider in the industry with USB 3.0 connectivity for the OnSemi KAI-16070 sensor.

The OnSemi sensor has a 35 mm optical format with large 7.4 x 7.4 micron pixels for superior dynamic range. The camera has a dynamic range of 66.7 dB and a full well capacity of just under 34,000 electrons, even without the built-in HDR mode. A USB 3.0 interface, on-board HDR imaging, and industrial reliability make the Lt16059H a leader in the market and a perfect candidate for the digital archival of film.

Lt16059H Highlights

Bit Depth 14 bits per pixel
Dynamic Range 64 dB
Pixel Size 5.5 x 5.5 µm
Optical Format 35 mm (43.47 mm diagonal)
Frame Rate 6 fps at full resolution
Resolution 6576 x 4384 pixels
Warranty 4 years

Future Considerations – The Lt29059

With the growing demand for high resolution, the first 5 k displays started appearing in 2014. Lumenera is currently introducing the Lt29059 to meet the demand for resolution imaging. The Lt29059 is a 29 megapixel variant of the Lt16059H, and is capable of capturing more than 6 k resolution, and imaging at 6576 x 4384 pixels. These features allow the Lt29059 to capture archival data that will be rich in detail and compatible with future displays.

Resolution Comparison: TV standards & Lt29059

Resolution Comparison: TV standards & Lt29059

Lt29059 Highlights

Bit Depth 14 bits per pixel
Dynamic Range 64 dB
Pixel Size 5.5 x 5.5 µm
Optical Format 35 mm (43.47 mm diagonal)
Frame Rate 6 fps at full resolution
Resolution 6576 x 4384 pixels
Warranty 4 years

This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.

For more information on this source, please visit Lumenera Corporation.

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