Cutting colourful chores

A computer-assisted method for converting black and white images and movies into colour has been developed by researchers at the Hebrew University of Jerusalem.


A computer-assisted method for converting black and white images and movies into colour has been developed by researchers at the Hebrew University of Jerusalem’s Benin School of Computer Science and Engineering.



The method is said to be less expensive and time-consuming than earlier colourisation methods developed in the late 20th century and which were used to convert to colour several classic black-and-white motion pictures such as “Casablanca.”



A major difficulty with colourisation has been its labour-intensiveness. In order to add colour a still image an artist typically begins by dividing the image into regions, and then proceeds to assign a colour to each region. There is no fully automatic way to reliably perform this task, since automatic algorithms often fail to correctly identify fuzzy or complex region boundaries, such as the boundary between a subject’s hair and face. Hence, the artist is often left with the task of manually delineating complicated boundaries between regions.



Colourisation of movies requires, in addition, tracking regions, as movement occurs across the frames of a particular scene. Again, there have been no fully automatic and reliable region-tracking algorithms for accomplishing this.



Now, Dr. Dani Lischinski, Dr. Yair Weiss and graduate student Anat Levin have developed a new, interactive, colourisation process that requires neither precise, manual, region detection, nor accurate tracking.


The method is based on a simple premise: neighbouring pixels in space-time that have similar intensities should have similar colours. The user indicates how each region should be colourised by simply “scribbling” the desired colour in the interior of the targeted region, as viewed on a computer screen, instead of tracing its precise boundary.



With these user-supplied “hints,” the software developed by the researchers automatically propagates colours to the remainder of the image and from there to subsequent frames of the movie.



This new technique is said to offer a simple and effective interactive colourisation tool that drastically reduces the amount of input required from the user. In addition to colourisation of black-and-white images and movies, the technique is also applicable to selective recolouring, a useful tool for refining digital photographs and for achieving special effects.



A provisional patent application has been filed for the process.


To watch a video demonstrating the new technique, please click here. This may take some time to load on slow connections.