Assessment of X-Rite and Gretag

Assessment of X-rite and Gretag

By: Chao-Lung Yang Yan-Fu Kuo Dr. Jan Allebach

Purdue University School of Industrial Engineering, West Lafayette, IN 47907

May 30 2007

HP-PURDUE CONFIDENTIAL 1 Color Measurement Instrument

Gretag Macbeth Spectro Eye

z One in IE GRIS 210; one in ME 256

z Colorimetry: Spectrum (380nm to 730 nm), CIE L*a*b*, L*C*h (a*b*), ∆E*, XYZ (OPTIONAL)

z XYZ calculated from spectrum readings is very close to XYZ readings given by Gretag

z Densitometry: Density

X-rite DTP70

z One in IE GRIS 210

z Colorimetry: Spectrum, CIE L*a*b*, L*C*h (a*b*), ∆E*, XYZ

z Automatic sheet-fed

HP-PURDUE CONFIDENTIAL 2 Instrument Color Consistency Check

z Bi-weekly check on Gretag

z With Gretag ColorChecker

z Compare to history L*, a*, b*, and ∆E for all color patches

z (XYy readings given by ColorChecker is NOT reliable)

100 50 100 Yellow Yellow Yellow 90 Magenta 40 Magenta 80 Magenta Cyan Cyan Cyan White 80 White 30 White 60 Black Black Black 20 70 40

10 b*

60 a* L* 20 50 0 0 40 -10 -20 30 -20 -40 20 -30 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 days days days

HP-PURDUE CONFIDENTIAL 3 Color Measurement Procedure Document

z Title: color measurement acquisition process

z Color metrics: CIE ∆E76 ramp and ∆E94 MCDM

z Follows the measurement processes and metrics used by HP

HP-PURDUE CONFIDENTIAL 4 IE Gretag Repair on 11/9/2005

z IE Gretag keep doing accuracy check by measuring ColorChecker biweekly since Sept. 2004

z Since Oct. 7 2005, we began to see the deviated measurement

z Sent back for repair on 11/9/2005, and received on 2/1/2006 Comparison before and after IE Gretag repair

8 6 4 2 0 -2

dE76 from paper white -4 0 5 10 15 20 25 30 ColorChecker # diff. b/w 20060203 and 20040921 diff. b/w 20051021 and 20040921 diff. b/w 20051007 and 20040921

HP-PURDUE CONFIDENTIAL 5 Assessment of Instruments

z Investigate the difference between X-rite and Gretag

z 4 experiments were conducted Compare the mean of ΔE76 which is calculated from measured spectrum values » UV filter option of X-rite had been investigated first Compare the standard deviation of ΔE76 » Consistency of X-rite and Gretag Investigate the aperture size of X-rite Comparison of measuring time

z Purchased new instrument “X-rite” in Dec. 2005

HP-PURDUE CONFIDENTIAL 6 Comparison of Measured Mean ΔE76 and Standard Deviation (one sample, 5 times)

z One test page was measured 5 times by X-rite and Gretag to obtain spectrum values (wavelength 400~700 μm) Each time measure each patch once

z Use measured spectrum values to compute the ΔE76 value (distance from paper white, normalized) Based on the procedure suggested by Terry Nelson (see document “Color Measurement acquisition process”)

z Comparison Investigate the UV filter option of X-rite Compare mean of ΔE76 Compare variance of ΔE76 -> consistency issue

z Statistical analysis was provided on this comparison (95% confidence level)

HP-PURDUE CONFIDENTIAL 7 UV Filter Option z UV filter option provided by X-rite can filter out the UV portion when profiling targets printed on substrates containing optical brighteners (Xrite.com)

z Compute the difference of X-rite ΔE76 and Gretag ΔE76 (X-rite - Gretag)

z The measurement by X-rite without UV filter is closest to Gretag Suggest to use NO UV filter option in our grading procedure

X-rite ( with UV filter ) vs IE Gretag (no UV filter) X-rite ( no UV filter ) vs IE Gretag (no UV filter) Calculated from specturm values Calculated from specturm values X-rite DE76 - Gretag DE76 X-rite DE76 - Gretag DE76 3 3 2 2 1 1 0 0 0% 20% 40% 60% 80% 100% 120% Cyan Cyan -1 0% 20% 40% 60% 80% 100% 120% Magenta -1 Magenta -2

DE76 Yellow -2 DE76 Yellow -3 Black -3 Black -4 -4 -5 -5 -6 -6 patch (%) patch (%)

HP-PURDUE CONFIDENTIAL 8 Comparison of Mean of ΔE76 X-rite vs Gretag (5 samples) z No filter

Comparison of mean of DE76 (Cyan) Comparison of mean of DE76 (Magenta)

120 120 100 100 80 80 60 60 DE76 DE76 40 40 20 20 0 0 0% 20% 40% 60% 80% 100% 120% 0% 20% 40% 60% 80% 100% 120% patch (%) patch (%)

Gretag X-rite (NO filter) Gretag X-rite (NO filter)

Comparison of mean of DE76 (Yellow) Comparison of mean of DE76 (Black) 120 120 100 100 80 80 60 60 DE76 40 DE76 40 20 20 0 0% 20% 40% 60% 80% 100% 120% 0 0% 20% 40% 60% 80% 100% 120% patch (%) patch (%)

Gretag X-rite (NO filter) Gretag X-rite (NO filter) HP-PURDUE CONFIDENTIAL 9 Comparison of Mean of ΔE76 (cont’) X-rite vs. Gretag (5 samples)

z Cyan and Black has smaller difference between X-rite and Gretag

z Magenta and Yellow has larger difference in higher density levels (red number marks diff. of ΔE76 > 1)

HP-PURDUE CONFIDENTIAL 10 Comparison of Mean of ΔE76 IE X-rite vs ECE X-rite

z No filter

z Sample number: 5

IE X-rite vs ECE X-rite (IE X-rite - ECE X-rite) (mean of dE76)

DE76 from paper white paper from DE76 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Patch (%) Cyan Magenta Yellow Black

HP-PURDUE CONFIDENTIAL 11 Comparison of Consistency

z Standard deviations were computed based on 5 samples

z X-rite has better consistency against Gretag (X-rite measures the same spot of each patch in a test-page)

Comparison of standard deviation Comparison of standard deviation X-rite (no filter) Gretag

1.2 1.2 1 Cyan 1 Cyan 0.8 Magenta 0.8 Magenta 0.6 0.6 DE76 Yellow

DE76 Yellow 0.4 0.4 Black Black 0.2 0.2 0 0

0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% patch (%) patch (%)

HP-PURDUE CONFIDENTIAL 12 X-rite’s Aperture

z Design several samples and measured by X-rite to investigate The size of X-rite’s aperture (mm 2) Measuring behavior of X-rite

z Central series of patches is the reference 2 2 7mm 6mm Shift distance 2 2 1 15 1 15 1 2 2 2 14 2 14 2 0 2 2 3 13 3 13 3 0.5 2 2 4 12 4 12 4 1 2 2 5 11 5 11 5 1.5 2 2 6 10 6 10 6 2 2 2 7 9 7 9 7 2.5 2 2 8 8 8 8 8 3 2 2 9 7 9 7 9 3.5 2 2 10 6 10 6 10 4 2 2 11 5 11 5 11 4.5 2 2 12 4 12 4 12 2 2 13 3 13 3 13 2 2 14 2 14 2 14 15 15 15

HP-PURDUE CONFIDENTIAL 13 Aperture Size

z Different patch sizes are measured by X-rite in a single sample

z The measurements of patches bigger than 6mm2 are consistency

z The suggested patch size should not be smaller than 6mm2 (no information about aperture on X-rite manual)

z The measures on the central series appears to be different from other series

Gradually

smaller Series #1 Series #2 Series #3 1 152 2 142 X-rite Aperture 3 132 (Measure on different patch size) 2 4 12 6 mm2 5 112 80 6 102 70 7 92 60 8 82 50 Series1 9 72 40 Series2 10 62 30 Series3 11 52 20 OK 12 42 10 13 32 white) paper (from De76 0 14 22 051015 15 # of patch

HP-PURDUE CONFIDENTIAL 14 Aperture Size (cont’)

z Series 1 and 3 are 7mm2 and 6mm2, respectively (for double-check)

z 7 mm2 and 6mm2 series are measured correctly

z In this case, results show X-rite can measure “side-line” patches better than central line (possible reason might be the correlation with size of alignment marks) 2 2 7mm 6 mm 1 152 2 142 3 132 X-rite Aperture (Measure on 6mm squart and 7mm squeart 4 122 target) 5 112 2 6 10 70 2 7 9 60 2 7mm squart 8 8 50 9 72 40 Series (from 15mm to 2 10 6 30 2 mm) 2 OK 11 5 20 6mm squart 2 12 4 10 2 13 3 white) paper De76 (from 0 2 14 2 0 5 10 15 15 # of patch

HP-PURDUE CONFIDENTIAL 15 X-rite’s Measuring Position

z Check the position of measuring aperture

z Series 1 are 6 mm2 patches moving from left to right (0.5 mm each)

z Series 3 are 6 mm2 patches moving from right to left (0.5 mm each)

z Measuring position is on the center of the patch based on the 15mm2 alignment marks (we also use 15mm2 alignment marks on our data harvesting test-page)

Shift distance Series #1 Series #2 Series #3 1 2 0 Xrite Aperture 3 0.5 Measure on different position of patch (6mm squart) 4 1 The same position 5 1.5 70 6 2 60 7 2.5 8 3 50 Series1 9 3.5 40 Series2 The same 10 4 30 Series3 position 11 4.5 12 20

13 De76 (from paper white) 10 14 0 Off region 15 0 5 10 15 # of patch

HP-PURDUE CONFIDENTIAL 16 Comparison of Measuring Time

z Measuring time of X-rite and Gretag Measure density values and spectrum values at the same time Gretag » Moving Gretag on the test-page » Data is stored in Excel (immediately stored when pushing bottom) » Total measuring time is around 120 second for 48 patches X-rite » Feeding test-page to X-rite » Data is saved by manually operation (5 seconds) » Measuring time is around 25 seconds for 48 patches » Total time is 30 seconds

z X-rite is much faster than Gretag

HP-PURDUE CONFIDENTIAL 17 Conclusion

z X-rite has better measuring performance than Gretag Shorter measuring time (30 second vs. 120 second) Good consistency

z Other advantages Better visualization function and data management on embedded software (Colorport software) Automatic calibration Alleviate labor fatigue

z Drawbacks Higher difference on Magenta and Yellow (in high density levels)

z Should use patch size larger than 6 mm2

HP-PURDUE CONFIDENTIAL 18