Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Analysis of Spectrophotometer Specular Performance Using Goniophotometric Information David R. Wyble Munsell Color Science Laboratory Rochester Institute of Technology

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 All integrating sphere spectrophotometers are not created equal Standards allow a wide range of conforming devices Sample gloss and specular port configuration can significantly affect measurements Introduction

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 A Pathological Case Reflectance factor

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 A more expected example… Reflectance factor

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Determine a relationship between the size of the specular port and the effective performance of the spectrophotometer in SPEX mode Create a method to correct measurements to allow comparison of results from instruments of differing configurations Purpose

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry Theory on Effective Specular Port Size Samples and Goniometric Measurements Results & Conclusions Outline

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry 1.4 Illuminating and viewing conditions for reflecting specimens c) Diffuse/normal (symbol d/0): The specimen is illuminated diffusely by an integrating sphere. The angle between the normal to the specimen and the axis of the viewing beam should not exceed 10°. The integrating sphere may be of any diameter provided the total area of the ports does not exceed 10% of the internal reflecting sphere area. The angle between the axis and any ray of the viewing beam should not exceed 5°. c) Diffuse/normal (symbol d/0): (Similar angular specifications)

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Reflectance: d/8 SPEX Detector Baffle Incident light 8° viewing, diffuse illumination, SPIN Sample Specular cap “black cap” excludes

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Reflectance: 8/d SPEX Detector Baffle Incident light Diffuse viewing, 8° illumination, SPEX Sample

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry 1.4 Illuminating and viewing conditions for reflecting specimens c) Diffuse/normal (symbol d/0): The specimen is illuminated diffusely by an integrating sphere. The angle between the normal to the specimen and the axis of the viewing beam should not exceed 10°. The integrating sphere may be of any diameter provided the total area of the ports does not exceed 10% of the internal reflecting sphere area. The angle between the axis and any ray of the viewing beam should not exceed 5°.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry 1.4 Illuminating and viewing conditions for reflecting specimens c) Diffuse/normal (symbol d/0): The specimen is illuminated diffusely by an integrating sphere. The angle between the normal to the specimen and the axis of the viewing beam should not exceed 10°. The integrating sphere may be of any diameter provided the total area of the ports does not exceed 10% of the internal reflecting sphere area. The angle between the axis and any ray of the viewing beam should not exceed 5°.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry 1.4 Illuminating and viewing conditions for reflecting specimens Note 1: For the conditions ‘diffuse/normal’ and ‘normal diffuse’ the regularly reflected component of specimens with mixed reflection may be excluded with a gloss trap. If a gloss trap is used, details of its size, shape, and position should be given,

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry By inference, the angle from the normal to the gloss trap will not exceed 10°.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry No guidance on angular size of gloss trap.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 CIE 15.2 Colorimetry All we are told about the specular port is to report the configuration used Still a range of configurations that meet the specification

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Specular Port Size As port size grows …

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Specular Port Size … more of the specular information …

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Specular Port Size … is lost …

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Specular Port Size … but how much?

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Where do we go now? We need to know the details of how our instruments handle this component of the reflected light.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Where do we go now? To do this, we first need to accurately characterize a set of samples, by measuring their reflectance characteristics as a function of angle.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 MCSL Goniometer Light sourceIR filterCollimator Sample holder

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 MCSL Goniometer Technical description Light source 100 cm sphere 2 interior 19.6V GE bulbs Lamp current monitored and manually maintained at 6.00A IR filter Collimation lens Detector Photoresearch PR704 spectroradiometer Aperture ~ 3° Measurement units are integrated radiance

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 MCSL Goniometer Technical description Sample and detector angles independently adjustable within physical constraints Vernier scales allow repeatable angle settings to 0.5°

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 MCSL Goniometer Sample Physical constraints limit measurement angles to -8° to +75°, always referenced to the specular angle. Incident light   0° Detector

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Theory Measure spectral reflectance using SPIN and SPEX modes Calculate the average difference between SPIN and SPEX data, in percent reflectance Determine the effective size of the specular port that would account for the above difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 SPIN and SPEX

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Theory Measure spectral reflectance using SPIN and SPEX modes Calculate the average difference between SPIN and SPEX data, in percent reflectance Determine the effective size of the specular port that would account for the above difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Average Spectral Difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Theory Measure spectral reflectance using SPIN and SPEX modes Calculate the average difference between SPIN and SPEX data, in percent reflectance Determine the effective size of the specular port that would account for the above difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Effective Specular Port Calculation Measure radiance vs angle on goniometer Calculate cumulative volume as a function of radius Determine the radius that results in the percent cumulative volume that matches the SPIN-SPEX difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Radiance Detection angle Radiance

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Radiance vs 2D Detection Angle

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Effective Specular Port Diameter Measure radiance vs angle on goniometer Calculate cumulative volume as a function of radius. Normalize this volume to the average reflectance data for the sample. Determine the radius that results in the percent cumulative volume that matches the SPIN-SPEX difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Cumulative Volume vs Radius

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Effective Specular Port Calculation Measure radiance vs angle on goniometer Calculate cumulative volume as a function of radius Determine the radius that results in the percent cumulative volume that matches the SPIN-SPEX difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Effective Specular Port Calculation

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Effective Specular Port Calculation current radius volume inside that radius r eff

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Effective Specular Port Calculation effective radius equation: Search through radii until we match the average SPIN-SPEX spectral difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Searching… Detection angle radiance

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Searching… radiance Detection angle

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Searching… radiance Detection angle

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Searching… radiance Detection angle

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Searching… radiance Detection angle

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Found “SPIN”-“SPEX” SPIN = total radiance Detection angle

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental: Spectrophotometers Four commercial-grade benchtop devices: –Datacolor Spectraflash 600+ –Macbeth Coloreye 7000 –BYK-Gardner The Color Sphere –Minolta 3600-d All are d/0 devices All have reasonable calibration status

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental: Spectrophotometers Specifically chosen for their range of specular port configurations, from <1” to 2” One (Minolta) has a detector in place of the specular port. SPIN and SPEX are calculated using the signal gathered by that detector

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental: Samples Two different automotive plastic samples (gray, tan) Three levels of gloss Total of five samples, two highly glossy, and three at two levels of matte surface Underlying color identical, since various gloss levels are stamped in the same piece of plastic

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental: Samples

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental: Sample Set ColorDescription gray Glossy Smooth Matte Rough Matte tan Glossy Smooth Matte

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental: Samples Smooth matteRough matte

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 For Reference: Measured Gloss ColorLevel20°60°85° gray glossy smooth matte rough matte tan glossy smooth matte

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Goniometric Results: measured radiance Note alternate ordinate axis for glossy samples.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental Results: Cumulative volume

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental Results: Cumulative volume

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental Results: Effective Specular Port Size (°) *** Minolta 3600-d has specular sensor Datacolor SF600 Macbeth CE7000 BYK- Gardner TCS Minolta 3600-d Gray Glossy Gray Smooth Matte Gray Rough Matte Tan Glossy Tan Smooth Matte “Actual” ***

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental Results: Effective Specular Port Size (°) CE7000 TC S SF6000+

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Experimental Results: Effective Specular Port Size (°) Minolta data at arbitrary port width

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Assumptions and Limitations or “Opportunities” Specular port vs sphere wall Specular port uniformity More comprehensive sample set Viewing/illumination beam Relationship to Gonio collimation

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Conclusions Overall trend among spectrophotometers agrees with the physical measure Ability to compare traditional designs to those with electronic port detection May aid in device selection to best accommodate the application Goal of inter-instrument correction not realized

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 Acknowledgements This work was supported by the Munsell Color Science Laboratory Special thanks are due to: –Danny Rich –Mark Fairchild –Roy Berns –Mitch Rosen who all helped tremendously with many fruitful discussions and s.

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002 That’s all. Thanks for listening!