1. ASSESSMENT OF DAYLIT GLARE PARAMETERS WITH IMAGING LUMINANCE MEASURING DEVICES (ILMD) AND IMAGE PROCESSING Porsch, Tobias; Schmidt, Franz

2. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 2 Outline What is the aim of this study? Prior studies & applications –Veiling glare-spread function (L v ) –Threshold Increment (TI) –UGR (Unified Glare Rating) Theoretical & practical realisation –Vertical illuminance (E v ) –Positioning index (p) –Threshold luminance –Calculating the Daylight Glare Probability (DGP) Tests and verification Conclusion Aim Prior studies & apps Realisation Tests Conclusion

3. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 3 What is the aim of this study? Developing an easy to use tool for the assessment of discomfort glare parameters based on imaging luminance measuring devices (ILMD) Used hardware: LMK mobile advanced (Canon EOS 450D qualified for measuring luminances) circular Fisheye lens (Sigma F2.8/4.5mm EX DC) Used software: LMK LabSoft (luminance image analysis software) MS Excel Aim Prior studies & apps Realisation Tests Conclusion

4. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 4 Prior studies & applications Aim Prior studies & apps Realisation Tests Conclusion Veiling glare-spread function (Lv) Threshold Increment (TI) UGR (Unified Glare Rating) = observing angle c = age depending constant n = 2 (common use)

5. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 5 Theoretical & practical realisation L source = luminance of the glare source L ambient = luminance of the ambient (adaptation luminance) Ω source = solid angle of the glare source to the area it illuminates,  = spatial position of the glare source ( = 0° viewing direction) Aim Prior studies & apps Realisation Tests Conclusion Most glare indexes bases on classified ‘glare’ luminances L S ( ϑ, ϕ ) related to its spatial positions ( ϑ, ϕ ), to its solid angles Ω S and to the state of adaptation of the subject’s eye – i.e. the ambient luminance L A or there caused vertical illuminance E V.

6. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 6 Theoretical & practical realisation Aim Prior studies & apps Realisation Tests Conclusion The first task in using ILMDs is to evaluate luminances “as seen” in the image – using high dynamic range algorithms OECF calibration optical calibration (i.e. vignetting) absolute calibration

7. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 7 Coordinate transformation rules Theoretical & practical realisation Aim Prior studies & apps Realisation Tests Conclusion The second approach is to combine the luminance information with the position information of the measured luminance values for extracting additional relevant information – geometrical adjustment.

8. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 8 Theoretical & practical realisation Aim Prior studies & apps Realisation Tests Conclusion The information is used to summarize the solid angle of a detected luminance source and hence to calculate the vertical illuminance out of this data: The result of the performed geometrical adjustment and calculation is an index image for the solid angle increment of each pixel:

9. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 9 Theoretical & practical realisation The Position Index P is calculated according to the proposal of the IES for the visual field above and the equations by Iwata and Tokata for the visual field below the line of sight. Aim Prior studies & apps Realisation Tests Conclusion The main focus at the current state of our studies was on the measurement of the Daylight Glare Probability (DGP) by Wienold.

10. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 10 Theoretical & practical realisation Aim Prior studies & apps Realisation Tests Conclusion The DGP requires to indicate a luminance threshold level which is needed to define light sources in the field of view as a glare sources or rather as a part of the background. Three principle methods were tested: using the average luminance of the entire image multiplied by factor x (x = 4) using a task zone area for averaging a threshold luminance analysing the luminance histogram of the entire image to adjust the threshold level as proposed by Wolf for the UGR assessment

11. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 11 Theoretical & practical realisation Aim Prior studies & apps Realisation Tests Conclusion To perform all steps before and inside the calculation formula for the DGP a MS Excel based user interface is used. This front-end has direct access to LMK LabSoft image analysis software, via ActiveX.

12. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 12 Theoretical & practical realisation Aim Prior studies & apps Realisation Tests Conclusion

13. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 13 Tests and verification Aim Prior studies & apps Realisation Tests Conclusion The major possibility to establish a measurement series for comparisons of the calculated DGP was given with the use of the ‘evalglare’ tool. In a first step a software tool was created to convert the 4 byte luminance image format *.pf into 4 byte RGB *.pic format for the Radiance image viewer tool. In the next step the ‘evalglare’ tool was used to perform the glare analysis: >> evalglare -d -c %str%_small.pic -y %str%_small.pic

14. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 14 Tests and verification Aim Prior studies & apps Realisation Tests Conclusion Simultaneously to the High-Dynamic luminance capturing a comparison measurement for the vertical illuminance with a Luxmeter was made. The comparison of the results shows a high correlation of the vertical illuminance for both: –Luxmeter and luminance image calculation  the used solid angle correction is reliable –Luxmeter and the ‘evalglare’ calculation  the image conversion is correct –additionally the correlation of the average luminances is high  the image conversion is correct

15. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 15 Tests and verification Aim Prior studies & apps Realisation Tests Conclusion

16. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 16 Tests and verification Aim Prior studies & apps Realisation Tests Conclusion The comparison of the calculated DGP results shows also a high correlation.

17. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 17 Tests and verification Aim Prior studies & apps Realisation Tests Conclusion Case study: situation number 6 shows a higher mismatch of the DGP result can be found. E vert (LMK) E vert (evalglare) Lave 90° (LMK) Lave (evalglare) 48,8 lx45,8 lx18,96 cd/m²18,1 cd/m² DGP (ave_evalglare)DGP_histDGP_aveDGP_task 16,56%19,94%19,80%19,88%

18. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 18 Conclusion Aim Prior studies & apps Realisation Tests Conclusion ILMDs are mainly used for the assessment of glare values. This is currently state of the art and commonly used in a wide field of scientific researches, concerning this topic. Simplifying the workaround by implementing heuristic identified formulas into image processing algorithms can be a solution for non-experts to identify glare values under real environment conditions. Problems: High contrasts between ambient and glare source do generate scattered light effects in the imaging system of the ILMD software scattered light correction (available) use of optimized imaging systems (available) Geometrical and photometrical imaging resolution mostly very small glare sources  dependance of the glare value from the geometrical resolution

19. 2nd CIE Expert Symposium on Appearance - When appearance meets lighting... page 19 Thank you for your attention!