Accuracy of srgb colour reproduction through a camera and a LCD imaging display

Transcription

1 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

2 Contents 1 Accuracy of colour reproduction 2 encoding transformation 3 colour Errors(Method & Result) 4 Conclusion

3 Accuracy of colour reproduction

4 Accuracy of colour reproduction NEC 95,100,111 LG 99,98,107 97,100,108 SONY 97,101,107 SamSung, Eizo,

5 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

6 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)

7 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

8 Encoding

9 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 or if R G B R G B = = = R G B ' ' ' R G B = = = ' ( R + ' ( G + ' ( B ) ) )

10 Step 2: = B G R Z Y X Encoding Inverse transformation

11 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)

12 Encoding well suited to cathode ray tube(crt), flat panel displays, television, scanners, digital camera and printing systems - ISO

13 Question 1Reference display 2 Reference observer 3 Viewing condition Encoding Transformation

14 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?

15 Camera: Equipment Used A full-frame (36 24mm) SLR professional Cannon-1Ds with a mm zoom lens LCD : A 21 inch EIZO CG210 LCD

16 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

17 Implement in imaging chain (Camera - LCD) profile Measured XYZ Camera LCD Measured XYZ E ab E 00

18 colour Errors Whole system (camera-lcd) CCC: Macbeth ColorChecker chart

19 colour Errors Whole system (camera-lcd) CCC: Macbeth ColorChecker chart

20 Errors 1 reproduction of digital camera 2 reproduction of LCD 3 encoding transformation

21 Accuracy of reproduction of digital camera inverse encoding transformation Measured XYZ Camera Calculated XYZ E ab E 00

22 colour Errors Only digital camera CCC: Macbeth ColorChecker chart

23 colour Errors Only digital camera CCC: Macbeth ColorChecker chart

24 colour Errors Compare between imaging chain and digital camera-only Camera-LCD camera CCC: Macbeth ColorChecker chart

25 The accuracy of Reproduction of LCD Inverse encoding Transformation Calculated XYZ LCD Measured XYZ E ab E 00

26 colour Errors Only LCD

27 colour Errors Only LCD LCD

28 The accuracy of encoding transformation encoding Transformation Inverse encoding Transformation Measured XYZ Calculated XYZ E ab E 00

29 colour Errors The accuracy of encoding transformation CCC: Macbeth ColorChecker chart

30 colour Errors The accuracy of encoding transformation Macbeth ColorChecker chart Kodak Q-60

31 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

32 Further work Ongoing work has shown that custom profile methods result in smaller errors