Accuracy of colour reproduction through a camera and a LCD imaging display Kyung Hoon, OH* Sophie, Triantaphillidou Ralph E, Jacobson *Hoh2@wminacuk Imaging Technology Research Group, University of Westminster http://wwwwminacuk/mad/page-1626
Contents 1 Accuracy of colour reproduction 2 encoding transformation 3 colour Errors(Method & Result) 4 Conclusion
Accuracy of colour reproduction
Accuracy of colour reproduction NEC 95,100,111 LG 99,98,107 97,100,108 SONY 97,101,107 SamSung, Eizo,
Accuracy of colour reproduction Profile Profile 97,100,108 97,100,108 Profile Profile ICS Profile Profile 97,100,108 ICS: Independent Colour space 97,100,108
Accuracy of colour reproduction profile ICS Profile ICS: Independent Colour space Methods [sharma] 1 Prcoess profile (ie, SWOP) 2 Generic Profile (ie Epson 2000P) 3 Custom Profile (ie Polynominal regression, GOG)
Accuracy of colour reproduction 1Reference display 2 Reference observer 3 Viewing condition Digital Camera profile ICS: La*b* profile LCD 97,100,108 ICS: Independent Colour space 97,100,108
Encoding
Encoding Inverse transformation Step 1: ' R G B ' ' = ( R = ( G = ( B 8bit 8bit 8bit BDC) /( WDC BDC) /( WDC BDC) /( WDC BDC) BDC) BDC) BDC is a black digital count and a white digital count is WDC (8-bits/channel) if R G B 004045 or if R G B 004045 R G B = = = R G B ' ' ' 1292 1292 1292 R G B = = = ' ( R + ' ( G + ' ( B + 00055 ) 1055 00055 ) 1055 00055 ) 1055 24 24 24
Step 2: = B G R Z Y X 09505 01192 00193 00722 07152 02126 01805 03576 04124 Encoding Inverse transformation
Encoding The method to colour space is developed based on a cathode ray tube (CRT) display - Sharma Abhay, Understanding color management, 2004 It continues to be implemented in liquid crystal displays (LCDs) It is also the most popular encoding transformation, found in most contemporary digital acquisition devices (such as scanner and digital cameras)
Encoding well suited to cathode ray tube(crt), flat panel displays, television, scanners, digital camera and printing systems - ISO 61966-2-1
Question 1Reference display 2 Reference observer 3 Viewing condition Encoding Transformation
Question Is colour reproduction via encoding using a high end digital camera and an LCD correct? If there are errors, where in the imaging chain do they occur?
Camera: Equipment Used A full-frame (36 24mm) SLR professional Cannon-1Ds with a 28-135mm zoom lens LCD : A 21 inch EIZO CG210 LCD
Two Test targets : Equipment Used Macbeth ColorChecker chart (CCC) & Kodak Q-60 (ANSI standard T8 7/2) Measuring instruments: X-Rite spectrophotometer - for Kodak Q-60 Color-Eye 7000A spectrophotometer - for CCC Minolta CS-200 colorimeter - for colour patch on LCD CCC: Macbeth ColorChecker chart
Implement in imaging chain (Camera - LCD) profile Measured XYZ Camera LCD Measured XYZ E ab E 00
colour Errors Whole system (camera-lcd) CCC: Macbeth ColorChecker chart
colour Errors Whole system (camera-lcd) CCC: Macbeth ColorChecker chart
Errors 1 reproduction of digital camera 2 reproduction of LCD 3 encoding transformation
Accuracy of reproduction of digital camera inverse encoding transformation Measured XYZ Camera Calculated XYZ E ab E 00
colour Errors Only digital camera CCC: Macbeth ColorChecker chart
colour Errors Only digital camera CCC: Macbeth ColorChecker chart
colour Errors Compare between imaging chain and digital camera-only Camera-LCD camera CCC: Macbeth ColorChecker chart
The accuracy of Reproduction of LCD Inverse encoding Transformation Calculated XYZ LCD Measured XYZ E ab E 00
colour Errors Only LCD
colour Errors Only LCD LCD
The accuracy of encoding transformation encoding Transformation Inverse encoding Transformation Measured XYZ Calculated XYZ E ab E 00
colour Errors The accuracy of encoding transformation CCC: Macbeth ColorChecker chart
colour Errors The accuracy of encoding transformation Macbeth ColorChecker chart Kodak Q-60
Conclusion 1 The encoding gave inaccuracies in colour reproduction in the imaging chain used 2 The digital camera gave errors in colour reproduction 3 In the errors found in the digital camera, there should be the encoding errors 4 The LCD showed good colour accuracy 5 Clipped colours in encoding transformation also produced errors
Further work Ongoing work has shown that custom profile methods result in smaller errors