Colorimetric characterization of input media in motion picture

production Steffen Paul

The Norwegian Color Research Laboratory

Faculty of Computer Science and Media Technology

Gjøvik University College, Gjøvik, Norway

steffen.paul@hig.no http://www.colorlab.no

Presentation of master project, Gjøvik, and 2007-06-08

Introduction/Background

Significant changes in the movie production work flow

transition to digital technology Post production dominated by digital technologies

advanced color grading digital effects

But, preferred input medium is still analog film dynamic range larger gamut

lab

Movie production work flow

film set

preview

film-camera

Keyframe Onset

OCN (original camera negative)

telecine editing, postpro

Movie production work flow

Keyframe OnSet developed at Gjøvik University College in cooperation with

Drylab R&D Oslo initial color grading on the set reports (Images) are send to the lab serve as reference for the telecine operator

Goal

Simulate characteristics of film stock to images captured with a digital camera

Limitations dynamic range different gamut sizes

Models

XYZ RGB

Film stock

Digital camera

forward transformation

inverse transformation

RGB

Models

Indirect approach two models both devices are characterized seperatly maybe less precise, slower, but more flexible

Direct approach one model for each possible combination of film

stock/camera needed possibly more precise, faster, less flexible

Setup

Test images provided by Drylab R&D Oslo film stock scanned (.dpx format) images from digital camera (RAW files)

ICC profiles

Camera/scanner profiles (scnr) A2B tag no B2A tag (usually not needed)

Printer/monitor profiles (prntr, mntr) A2B tag and B2A tag (softproofing) profiling software expects measurement data to be in XYZ

(not RGB)

ICC profiles

Inversed profile measurement data and reference data swopped it works, but..

Regression

Indirect transformation determine the relationship between RGBcam, XYZref and

RGBfilm values Direct transformation

relationship between RGBcam and RGBfilm

RGB values measured from test images spectral data converted to XYZ values for each test target models created with regression module in ICC3D evaluation with trainigset and testset

Regression

Regression

Regression

Regression

Regression

Regression vs ICC profile

Kodak 200T deltaE76 deltaE00

Regression (3rd) 4,48 2,77

ICC profile 7,99 5,53

Conclusion

Project showed limited use of ICC profiles regression proved working

Test images show some problems underexposure non-uniform exposure clipped colors in test set

Future work

models for several types of popular film stock implementation in Keyframe OnSet

Thank you for your attention.