EndUser DLP Projector Colour Calibration Behnam Bastani, Brian Funt, Roozbeh Ghaffari behnam'bastani

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End-User DLP Projector Colour CalibrationBehnam
Bastani, Brian Funt, Roozbeh Ghaffaribehnam.basta
ni_at_hp.com, funt_at_sfu.ca, ghaffari_at_sfu.ca
Simon Fraser University
Color Calibration
Linear Transformation
Fast, Requires little memory Requires a linear
space
T1T2Tn (linearized space)
RGB
XYZ
Non Linear Transformation
Fast, Does not require linearity of input
space May not find a good mapping, requires a
long time training period
XYZ

• Mostly is based on some sort of learning
• Support Vector Regression (SVR)
• Neural Network

Look Up Table
Fast, Accurate Requires lots of memory, hard to
fill in the whole space
DLP Displays cannot be calibrated similar to CRT
or LCD displays
How many Basis are needed to predict DLP output
accurately?
LCD and CRT can be calibrated using a 3x3 matrix
Principal Component Analysis is used to find a
good candidate
PCA can be used to determine how many basis are
needed to predict the tristimulus values
accurately enough
For DLP, 3x3 matrix transformation cannot predict
light colours accurately
Dimension 4 and 7 models are good candidates
Predicting XYZ given RGB (Forward Direction)
Predicting RGB given XYZ (Backward Direction)
Wyble

• Lineraize R, G, B and Wmin(RGB) based on X, Y, Z
  and X resoponse of each channel
• Find a linear transformation from Linearized
  (RGBW) to XYZ

Wyble

• Estimate RGB using inverse of forward matrix M
• RGBtheoMxXYZ
• Remove White Filter subtracting tristimulus of
• Wtheomin(RGBtheo)
• De-Linearize the predicted Values

Masking
XYZ

• 3x7 matrix is not invertible.
• Try all 6 possible combination
• RM, RY, GC, GY, BC, BM
• A valid combination is the one that meets
• 255 gt (R,G or B) gt (C,M or Y) gt W gt 0

Modified Wyble
The matrix transformation is found by applying
least squares between linearized input and XYZ
Result
Masking

• Lineraize R, G, B, C, M, Y and W
• Find a linear transformation from Linearized
  (RGBCMYW) to XYZ

Forward
Backward

• References
• D. Wyble, M. Rosen, Colour Management of DLP
  Projectors, Proc. IST/SID 12th Colour Imaging
  Conference 2004, 228-232
• N. Tamura, N. Tsumura, Y. Miyake, Masking
  Model for accurate Colourimetric characterization
  of LCD Proc. IST/SID 10th Colour Imaging
  Conference 2002 p. 312-316
• B. Bastani, W. Cressman, and B. Funt,
  Calibrated Colour Mapping Between LCD and CRT
  Displays A Case Study, Colour Research and
  Application, (in press)