False-color image processing

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Imaging > Imaging Techniques > False-color image processing

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Introduction[edit | edit source]

False color image processing  is a technique that combines and rearranges the colour channels from one or multiple source images  that results in a final composite image in which the colours rendered do not match those that would be observed naturally by the human eye. These methods help visualize information not otherwise discernable which can aid in interpretation of media and materials present and inform further scientific analysis.

False-color processing provides a non-invasive means to analyze cultural heritage materials and gain a deeper understanding of their condition and creation and to inform preservation needs. With a wide range of applications deriving from a single image or image cube, false-color image processing has immense potential for comprehensive scholarly and conservation examination.

The most common False Color Imaging technique is the Infrared False Color, which combines the Red and Green channels of a visible-colour image with an infrared capture (either IR photography or IR reflectography). However, this process is not limited to only this imaging technique, as the range of techniques also includes Ultraviolet False Color Principal Component Analysis and others.

History and background[edit | edit source]

Before digital photography became more widespread, conservators and photographers could only rely on infrared photographic emulsions, among which the Kodak Ektachrome infrared film type 2236. Its three emulsion layers were sensitized to infrared (in the range between 750 nm and 900 nm), red and green wavebands respectively. It is therefore here that the traditional colour arrangement for the infrared false colour was born, and the same result is often sought after with digital image processing.

The earliest use of infrared false colour photography in the cultural field is reported in the late 1970s, where pigments, inks and glasses were first examined, but it was only in the 1990s that an attempt of standard procedure was proposed[1].

Definitions[edit | edit source]

Techniques[edit | edit source]

From single capture[edit | edit source]

False Color Infrared (FCIR)[edit | edit source]
False Color Reflected Ultraviolet (FCUV)[edit | edit source]
Chromatic and Infrared Chromatic (CHR and IRCHR)[edit | edit source]

From datacube[edit | edit source]

Principal Component Analysis (PCA)[edit | edit source]
Soft Independent Modelling of Class Analogies (SIMCA)[edit | edit source]
Spectral Angle Mapping (SAM)[edit | edit source]
Maximum Intensity Projected (MIP) / Particle Analysis[edit | edit source]

Workflows and best practices[edit | edit source]

How to interpret[edit | edit source]

Examples / Case studies[edit | edit source]

References[edit | edit source]

  1. Moon, Thomas, Michael R. Schilling, and Sally Thirkettle. 1992. ‘A Note on the Use of False-Color Infrared Photography in Conservation’. Studies in Conservation 37 (1): 42.