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14.11.20151 CIE Budapest 2009 | FG Lichttechnik | Peter Bodrogi et al. Re-defining the colour...

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03.07.22 1 CIE Budapest 2009 | FG Lichttechnik | Peter Bodrogi et al. Re-defining the colour rendering index Peter Bodrogi Stefan Brückner Tran Quoc Khanh
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Page 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.

20.04.23 1CIE Budapest 2009 | FG Lichttechnik | Peter Bodrogi et al.

Re-definingthe colour rendering index

Peter BodrogiStefan BrücknerTran Quoc Khanh

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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)

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New questionnaire

Variable R

Variable P

VariableEvis

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New definition of the colour rendering index based on computed ratings

5.57.25

9.5

13.7

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New definition of the colour rendering index:histograms of the computed ratings

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CRITU_DA_1 = (100/5) (6 - Median [{RCi} i=1…17])

New definition of the colour rendering index1: median scale (coarse)

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Comparison of CRITU_DA_i with Ra (1-8) and Ra (1-14) and with CQS7.1

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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

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New colour rendering index: our point of viewAdditional index for inter-observer variability

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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

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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 samplesValidate the scale of the new CRI_Darmstadt (very good-very bad)

Develop the inter-observer variability indexTabletop (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

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