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Jan Hubička edited this page Jan 5, 2025 · 69 revisions

Color-Screen

Color-Screen is a collection of tools for working with digitized versions of additive screen processes of early color photography.

Example
Flowers, Paget lantern slide 8x8cm, ca 1921 (left) and digital color reconstruction (right)

What is an additive color screen process?

Additive color screen processes used panchromatic negatives exposed through a color screen filter similar to the Bayer filter color pattern of today's CCD and CMOS camera sensors. The negative was then copied to (black and white) transparency which yielded a color picture when viewed through the viewing screen filter. While any given point in the image would appear as only one of three colors, the dithering of these colors would (with varying levels of success depending on the specific process) seem to mix to the eye giving a smooth appearance of a full color palette. These were some of the earliest ways photographers and cinemaphotographers created color imagery, and so many of the earliest (and in some cases only) color images of a given person, place, or event were captured using additive color screen processes. The technical nature of these processes present unique challenges to capture, preservation, restoration and presentation. Note that while some of these processes were used in both still photography and cinema the focus of this toolset is still images

What we aim for?

Our tool offers (by now quite powerful) set of features for digitally restoring and enhancing early color photographs:

  • Accurate Color Rendering of negatives taken using color screen processes: Transform digital versions of negatives captured with additive color screen filters (which looks monochromatic and encode colors spartially) into vibrant color photographs with high degree of accuracy. By understanding individual color processes and original dyes used to produce the color filters, we can restore photographs into colors as they looked new.
  • Accurate color Restoration of transparencies: Most transparencies made using additive color processes faded or misregistered. These layered structures, containing a black and white slide and a color filter, can be digitally restored to original colors based on high-resolution digital capture ideally made including the infrared channel.
  • Enhanced Display and Printing: Ensure your early color photographs are ready for digital screens and physical prints. Traditional scans of these photographs often suffer from accentuated color screen patterns and color shifts. We use specialized demosaicing algorithms that recognize the specific color screen used. This allows us to create smoother digital files that preserve the image's fine details without introducing unwanted artifacts.
  • Stitching of scans made in multiple tiles: By understanding the geometry of color screen used to take the image, we can stitch individual tiles of scan with greater precision then it is achievable by general purpose panorama stitching tools. This precision is, in fact, necessary since the fine pattern almost never stitch without specialised care.
  • Quality checking: Digitizing early color photographs needs a special care. As a side-effect, the color screen filters can serve as very useful calibration targets which is present in every capture. Our tools can check if the color screen is rendered in a sufficient detail to resolve individual color patches, if there are geometric distortions or vibrations, if the highlights and shadows are preserved and also verify uniformity of the sharpness across of the digital capture the whole image.
  • Evaluating aging of additive color photographs: We can measure geometrical changes in the original (film base shrinking) and estimate degree of color fading. Some of the processes, especially Dufaycolor, can suddenly decompose in a matter of months, see E. Siegel: Filmbase Deterioration in Dufaycolor Film. We hope to eventually understand this and be able to check if a given original is in a good physical condition.
  • Understanding the processes: We developed a digital laboratory which can simulate additive color processes and can be used, for example, to verify validity of published specifications of color dyes, spectral responses of emulsions and other aspects of historical processes.
  • Understanding photographers: We can reliably detect when early color image was manipulated by the photographer (retouched by hand).

A Call to Collaboration

Early color photography is a fascinating and often under-appreciated field.

Collections of photographs captured using these early processes are rare and tend to be small. While individual collections might not warrant extensive digitization efforts on their own, together they represent a vast and irreplaceable historical record.

We are eager to connect with other researchers in this area to collaborate on digitizing, restoring, and sharing these collections. We believe our tools, developed over two years of active research, can be instrumental in bringing these forgotten photographs back to light.

If you have a collection of early color photographs, or know of researchers or photographers working in this field, or are interested in anything related to this area we'd love to hear from you. Our goal is to build a comprehensive set of tools that will make these unique pieces of history accessible to everyone. Please do not hesitate to write to Jan Hubička [email protected].

We are happy to focus on (sometimes surprising) problems that arise while digitizing collections of early color photographs. In 2023 we implemented color stitching tool to aid digitization of the collection of early color photographs of the National Geographic Society. Actual digitization was done by Digital Transitions Heritage. To our best knowledge, this is the first large collection of Dufaycolor photographs mass-digitized in sufficient quality which performs analysis of individual color patches. See our 2023 paper for details.

News

  • 2025, January 5: New manuscript "Understanding colors of Dufaycolor: Can we recover them using historical colorimetric and spectral data?" was added to Publications
  • 2024, September 9: Linda Kimrová's bachelor thesis Digital processing of early colour photography was defended
  • 2024, July 14: Color-Screen 1.0 released
  • 2024, July 8: Our talk proposal "Understanding colors of Dufaycolor" was accepted for 3rd Colour Photography and Film. See you in Amsterdam!

Software packages

Table of contents

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