1. 14.11.20151 CIE Budapest 2009 | FG Lichttechnik | Peter Bodrogi et al. Re-defining the colour rendering index Peter Bodrogi Stefan Brückner Tran Quoc Khanh

2. 214.11.2015 New colour rendering index: our point of view 1.In practice, a rank order scale may be more usable than a continuous scale 1.It is easy for the user to understand very good, good, acceptable, not acceptable and very bad 2.What is the visual difference between Ra=78 and 90? And between Ra=78 and 82? 3.New CIECAM02-based colour spaces like CIECAM02-LCD (Luo et al, CRA, 2006) 4.Define the category limits for very good, good, acceptable, not acceptable and very bad in a new visual experiment in terms of CIECAM02-LCD 5.Computed categories for a set of test colour samples, e.g. for a new white LED light source: skin: very good; banana: good; cucumber: acceptable; etc.  Compute from the above „rating vector“ a single quantity like its median and then the new CRI like 6-median(rating vector)

3. 314.11.2015 New questionnaire Variable R Variable P Variable  E vis

4. 414.11.2015 New definition of the colour rendering index based on computed ratings 5.5 7.25 9.5 13.7

5. 514.11.2015 New definition of the colour rendering index: histograms of the computed ratings

6. 614.11.2015 CRI TU_DA_1 = (100/5) (6 - Median [{R Ci } i=1…17 ]) New definition of the colour rendering index 1: median scale (coarse)

7. 714.11.2015 Comparison of CRI TU_DA_i with R a (1-8) and R a (1-14) and with CQS7.1

8. 814.11.2015 1.Separate indices for the users‘ different tasks 1.Naturalness or colour fidelity: the true appearance of simple standalone surface colours as under „A“ or „D65“ or from long-term colour memory 2.Saturation enhancement can be in a separate index (preference) 3.CPI for preference or „flattery“; CDI: small colour differences 4.HRI for harmony rendering (is the appearance of a combination of colours aesthetic?) 5.Visual clarity, large colour differences 6.Acceptability of realistic scenes with many colours 2.Every user can select an index appropriate for the task, e.g. fidelity can be important for textile designers 3.Or CDI for electricians working with wires 4.Weighting of the indices New colour rendering index: our point of view

9. 914.11.2015 New colour rendering index: our point of view Additional index for inter-observer variability

10. 1014.11.2015  CATs: mostly collected under two light sources (D65 and A)  Combinations of surfaces, textures and shapes can evoke higher order neural mechanisms affecting colour constancy: e.g. memory, language, or object recognition  Compare the colour constancy index (e.g. the Brunswick ratio) with the colour rendering index  Effects of local contrast, global contrast, and image content on chromatic adaptation  Relational colour constancy: spatial cone excitation ratios in a multi-colour- surface scene remain (relatively) constant under changing illuminations but this may not hold for novel artificial light SPDs  Chromatic textures in natural scenes: the discrimination of texture stimuli is not the same as the discrimination of uniform colour patches under the test and reference illuminants  Contextual factors: higher order processing involving long term colour memory for familiar objects (e.g. human skin tone). Pictorial (hyperspectral) test images are needed instead of standalone patches. New colour rendering index: future tasks

11. 1114.11.2015 The colour rendering index can be improved by advancing two lines of research:  1.computational colour constancy  2.colour image difference metric  Our planned experiments:  Double-chamber viewing booth experiments currently underway  Aim: 12 observers x 2 CCTs (2900K and 5000K) x 5 light sources x 20 test colour samples  Validate the scale of the new CRI_Darmstadt (very good-very bad)  Develop the inter-observer variability index  Tabletop (still life) with several coloured surfaces (textures, objects) and a test room with immersion in the visual environment (acceptability study) with several conventional and new light sources New colour rendering index: future tasks

12. 1214.11.2015