Vuescan Output Optimization

Vuescan: ver 9.0.19
Scanner: Epson V500
Mode: Reflective

                                              ΔE2000
 Color      Curve      Custom                              
Balance   Low - High    icc   Output  ave   90%   95%   max

None       default      No     aRGB   8.04 10.24 10.78 13.87  refer to fig.2
Neutral    default      No     aRGB   4.73  6.97  8.53 10.63
None       default      Yes    aRGB   5.57  6.85  7.09  9.33
Neutral    default      Yes    aRGB   4.36  5.82  6.34  7.18

None      0.10 0.25     Yes    wide   2.84  5.08  5.85  6.76  refer to fig.3
None      0.18 0.58     Yes    aRGB   2.60  4.74  5.42  6.82  refer to fig.4

Raw data was assigned Monaco profile
in CS4 and converted to aRGB with
a)  Absulute rendering intent         0.39  0.72  0.89  4.38
b)  Perceptual rendering intent       1.78  2.27  2.32  4.02

Epson generic reflective profile      2.15  3.39  3.93  5.77
    assigned in CS4


1) Reference data in Lab values

Figure 1

2) No optimization

Figure 2

3) Custom icc, fine tuned curve low and high, output with wide gamut RGB color space.

Figure 3

4) Custom icc, fine tuned curve low and high, output with wide Adobe RGB color space.

Figure 4

User defined illuminants in PM5

The Viewing Light Source option allows user defined illuminant into the generated profile.  Such option is only available when spectral data are used as reference set.

Referring to the followings.
All ΔEs are color differences with respect to the reference data. In general, profile generated with D65 viewing light source option has better skin tone reproduction.
                           ΔE2000
              D8     F7     G8     H8     F2
*D50-D50     1.98   2.23   1.90   1.84   2.73  
*D65-D50     1.48   0.77   0.47   1.07   1.95

*D50-D65     3.50   3.62   3.31   3.26   4.47
*D65-D65     2.81   1.99   1.60   2.38   3.47

*(profiled with D50/D65 viewing option)-(compared under D50/D65 illuminant) 

Compared with illumnant set to D50



Compared with illumnant set to D65

 




Spectral Reference for ColorCheckerSG

2 official reference sets are available.
a) Digital ColorChecker SG.txt  dated 5/12/2005
b) ColorCheckerSG.txt             dated 1/25/2007

ΔE between the 2 reference sets

Correlation Check - Imatest vs PatchTool





With Imatest

  




With PatchTool

 

Refer to this Link , section F: (Multicharts module of the Imatest), for possible issue on reference set used by Imatest.

Note:
Photoshop uses only D50 illuminant @ 2 degrees standard observer and that all data are assumed to be D50 values irregardless of the actual source/illuminant used.

x-rite Checker SG

Scanner color calibration is carried out by scanning a calibration target and determining the transformation that maps the scanner RGB values to the known or measured colorimetric data for the calibration target. The calibration is accurate over the medium represented by the calibration target, but it is less so over other media.
                           ΔE2000
               average   90%      95%      max
Profile
SG-MP           1.31     2.03     2.27     4.87    (ver 4.8)
SG-PM5          1.55     2.72     2.92     3.37    (ver 5.0.10)
Kodak-MP        4.14     6.89     7.21     8.77
Kodak-PM5       5.13     7.14     7.76     9.25
Heid-MP         4.08     7.05     7.27     8.67
Kodak-PM-98a    4.06     6.50     7.36     8.62
V500 Generic    3.66     6.71     7.09     8.76    (by Epson)    

Profiling of Digital Cameras with the Gretag-Macbeth Digital Color Checker SG
Profiling input devices

Veuscan's Raw Data

Image gamma value is defaulted to 1.0 for 48-bit rgb data and that for 24-bit rgb sample is 2.2.
It is normal that raw data saved with gamma 1.0 will appear much darker.

Raw data in 48-bit RGB

Raw data in 24-bit RGB (or AUTO)

The non color managed image with Epson Scan  is slightly darker compared with raw data using Vuescan set to 24-bit mode, and that the white point Lab data are ( 91,1,4) and (93,1,3) respectively.

No color managed rgb  (24- or 48-bit) output with Epson Scan

Choice of Gama
In general, best choice of gamma is between 2.2 to 2.4 for scanning at 8 bits per channel (24-bit per pixel).
Do not use linear gamma (gamma=1.0) unless you are working with 16 bits per channel (48-bit per pixel).
Gamma 2.4 is closest to perceptual space.
More than 2.4 (up to 3.0) may drop too much highlight.
Less than 2.2 may introduce loss of detail in shadows.

Choice of File Type
TIFF or BMP, depends on supported formats of your platform. Do not store it in JPEG for image to be used for profiling.

Optimising profile generated with PM5

By tweaking the data for white point and black point in the reference list, ΔE of color reproduction can be optimised with profile generated using PM5.

Summary of Result
a) The scanned data (non color managed) in TIFF was read with CS4, assigned with the designated profile and converted to ProPhoto color space.
b) RGB data was extracted with the scanner module in PM5
c) Extracted RGB data was read with PatchTool  and compared with reference list.
                           ΔE2000
               average   90%      95%      max
PM5(tweaked)    0.84     1.48     2.04     2.75
MP              1.69     2.21     2.31     2.70     (ver 4.8)
PM5             2.31     3.70     3.97     4.37     (ver 5.0.10)



Tweaked PM5 scanner icc profile

 

 



Optimal tuned




Over tuned