Don't use the e-mail address given in the presentation, but instead: web<dot>victor<dot>reijs@gmail<dot>com

1. Color optimization with
IFRAO standard scale
Victor Reijs, geniet2003@iol.ie
RASI-2004, Symposium P
Rock art conservation and management
Nov./Dec. 2004, Agra, India

2. Content
 Rationale of IFRAO standard scale…
 Reference color values…
 Optimizing pictures…
 Possible scale enhancement…
 Future steps…

3. Rationale of IFRAO
standard scale
 Determining size of object
 Focusing help for photographic equipment
 Providing an inexpensive scale
 Providing a means to do color optimization
 Find an objective and reproducible method to
optimize

4. Content
 Rationale of IFRAO standard scale…
 Reference color values…
 Optimizing pictures…
 Possible scale enhancement…
 Future steps…

5. Reference
color values (1/2)
 Macbeth ColorChecker
 http://www.brucelindbloom.com/ColorCheckerRGB.html
 IFRAO standard scale
 no reference color values available
 spectrophotometer measurements were
done for May 1994 and Nov. 2001 scales
 http://www.iol.ie/~geniet/eng/IFRAOcoloropt.htm#RGB …

6. Reference
color values (2/2)
 IFRAO standard scale:

7. Content
 Rationale of IFRAO standard scale…
 Reference color values…
 Optimizing pictures…
 Possible scale enhancement…
 Future steps…

8. Optimizing pictures
 Software…
 Results…
 Evaluation…

9. Software (1/3)
 Not publicly available for IFRAO card, but
available for Macbeth ColorChecker
 Transform-based method…
 bring picture from Γdevice into linear space
 transform RGB values by a 3*3 RGB matrix
 bring picture into ΓxRGB space (=2.2)
 check pictured scale against reference
color values and if necessary change
Γ and/or 3*3 RGB matrix

10. Software (2/3)

11. Software (3/3)
 Transform-based method (VR)
 ICE Color
 Utilizing Black-Gray-White droppers of
PaintShop Pro/Photoshop (BGW)
 Several others (inCamera, PSP8, iCorrect,
Color Pilot)

12. Optimizing pictures
 Software…
 Results…
 Evaluation…

13. Results (1/4)
 Pictures of Macbeth ColorChecker and
IFRAO scales using for instance fluorescence light:

14. Results (2/4)
 The IFRAO standard scale
is optimized
 Macbeth ColorChecker card is the Rock-art
 Difference/error between Rock-art and
reference color values:

15. Results (3/4)
 An increasing number of color
patches that are optimized
 Remaining color patches are the Rock-art
 Difference/error between Rock-art and
reference color values:
visible by eye
not visible by eye

16. Results (4/4)
Transform-based method (VR)
before after

17. Optimizing pictures
 Software…
 Results…
 Evaluation…

18. Evaluation (1/2)
 Rules during photography:
 No glare allowed on the scale
 Use the scale as gotten (so no protection)
 Have the scene lighted in the best contrast
and most uniform way possible
 Use uncompressed picture format types
when processing (like: tiff and bmp)
 Make sure that the usable area of each
color patch has at least 100 pixels
 Take time to follow-up these rules!

19. Evaluation (2/2)
 Transform-based method (VR)
has consistent results
 ICE Color looks most of the time oke:
http://www.iol.ie/~geniet/eng/icecolorhelp.htm
 Grays, hard colors and rock-art colors
perform equally well
 The more color patches used in the
optimization, the smaller the difference with
reference color values
 The number of colors (8) on the IFRAO
standard scale is considered small to do
extensive color optimization

20. Content
 Rationale of IFRAO standard scale…
 Reference color values…
 Optimizing pictures…
 Possible scale enhancement…
 Future steps…

21. Possible scale
enhancement (1/3)
 Small changes to IFRAO standard scale:
 remove glare
 no black-ink smudging
 bring green patch into sRGB space
 move macro scale to right (to increase
colors)
 provide an online FAQ

22. Possible scale
enhancement (2/3)
 Somewhat bigger changes:
 change black/white blocks (1 by 1 cm) into
contrast rich colors (1 by 2 cm)
 make color patches same size as gray
patches (1 by 2 cm)
 have colors evenly spread over rock-art
color gamut
 if wise; keep existing colors/grays in the
card for backwards compatibility
 This doubles the number of colors (16)

23. Possible scale
enhancement (3/3)
 PIETJE scale:
visible by eye
not visible by eye

24. Content
 Rationale of IFRAO standard scale…
 Reference color values…
 Optimizing pictures…
 Possible scale enhancement…
 Future steps…

25. Future steps
 Repeat spectrophotometer measurements to check
reproducibility of reference colors
 More throughout testing of promising color
optimization software
 Add diagnostic help to software
 Be able to determine automatically where the color
scale is
 Make the color optimization available as a web
service
 Determine how my proposed ideas (the small and
somewhat bigger changes) can help to evolve the
IFRAO standard scale

26. Acknowledgement
Thanks to many people,
of whom I want to specifically mention:
Tim Autiokari
Bruce Lindbloom
Robert Mark
Joseph Wilhelm

27. Thank you for listening
and let an open discussion start.
Please provide your feedback also to:
Victor Reijs, geniet2003@iol.ie
http://www.iol.ie/~geniet/eng/IFRAOcoloropt.htm