All Things Color for Film and Digital Cinema
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Posts Tagged ‘Scanning’

Log encoding for the Cineon/DPX file format – Density Pt.3


  As outlined in the original Kodak Reference Pages for the Cineon file format standard,   the Cineon or DPX file format is the world standard digital imaging format for digital motion picture images. Any DPX or Cineon frame can be opened by any film vendors’ hardware and be displayed in the correct format with the correct gamma encoding. (unlike formats such as quicktime!).

The Cineon file essentially is a digital replica of a motion picture negative (a digital negative). It is imaged and encoded such that it retains all the color and exposure information expressed in the negative and as such is encoded in a logarithmic manner. 

The Cineon format was primarily designed for Digital VFX and Animation artists to be able to work on film acquired sequences that could, when finished, be written back to film and intercut seamlessly with camera original negative. With the boost in enhanced graphics processors, the ever increasing capacity and speed of hard drives and some clever Code Boffins, entire films can now be digitally enhanced in the realm of the Digital Intermediate.

Film has traditionally been represented by a characteristic curve which plots density vs. log exposure. This is a log/log representation. In defining the calibration for the Cineon digital film system, Eastman Kodak Co. talked to many experts in the film industry to determine the best data metric to use for digitizing film. The consensus was to use the familiar density metric and to store the film as logarithmic data.” Kodak Reference.


The film scanner as a densitometer


The Spirit 4k Datacine

The Spirit 4k Datacine

Why all these posts on Densitometry?


Because for me to understand the nature of how a scanner accurately scans and represents the filmed dynamic values and colors of a scene I delved in to the science of  the sensitometry of film. 

The color film scanner functions very much like a densitometer. A light is passed through the film, detected and its optical density read by a sensor. In digital imaging, color needs to be defined by three components Red, Green and Blue. Each pixel on the array of the scanner reads the Color density of the section of the image hitting its photosite and converts the results into data values which are then read into a file for each frame. 

The understanding of things like densitometry and the sensitometry of film has helped me in being able to deliver the best most accurate scans that deliver the creative intent and the pure colorimetry of a scene. To come later will be posts on color cross talk and purity.