Method and apparatus for subject image tracking in high definition film-to-video color correction

DETAILED DESCRIPTION A method and apparatus for tracking the tone scale of a subject image which is being electronically transformed from a first medium to a second medium is disclosed.
In the preferred embodiment, a subject image is recorded onto polychromatic film, and is subsequently converted to a high definition video signal.
A film scanner optically scans the subject image on the film, and the film scanner separates the subject image into its three monochromatic optical film images.
The monochromatic optical film images are digitized and input to an image signal processing subsystem.
The image signal processing subsystem provides color correction for the three monochromatic channels.
In performing color correction, the image signal processing subsystem compensates for film and video characteristics that cause a degradation of color from the original subject image.
Before performing color correction on each channel, calibration of the image processing subsystem to the film scanner occurs.
To calibrate the image processing subsystem, an operator specifies white and black levels corresponding to highlight and shadow tones respectively.
Through use of an image range interface, an operator specifies, for each channel, a first signal level to correspond to the white tone level and a second signal level to correspond to the black tone level.
In this way, an operator may specify any range of tones, within the input signal range, to represent the white and black tone densities recorded on the film to correlate to tone densities on an output HDTV monitor.
The image signal processing subsystem also performs characteristic curve processing for each channel in accordance with a Hurter-Driffield (HD) characteristic curve.
The HD characteristic curve depicts the relationship between the film dye density and a logarithm of the relative film exposure.
The HD characteristic curve is derived from characteristic curve parameters which are dependent upon the type of film being scanned.
A characteristic curve interface is provided in the operator interface which allows an operator to enter and adjust both a base black exposure and a contrast range for the subject image