Brychtova - Evaluation of colour schemes usability in Atlas of the Phenological Conditions in Czechia

This presentation is co-financed by the European Social Fund and the state budget of the Czech Republic.

EVALUATION OF COLOUR SCHEMES USABILITYof the Atlas of Phenological Conditions in Czechia

Alžběta BRYCHTOVÁ

14th October 2014 | Olomouc | 3rd InDOG Doctoral Conference Evaluation of colour schemes usability…

Today…

a brief introduction of my PhD research summary of the most important experimental findings evaluation of sequential colour schemes of the Atlas of

Phenological Conditions in Czechia


Colour and Colour Distance in Cartography

Colour on maps improves the aesthetics of maps colour hue and value - 2 of 6 Bertin‘s visual variables

Colour distance metric, that allows to quantify perceived difference between

two colors (CIE, 2012)

how different levels of colour distance influence maps‘ readability?

what is the optimal colour distance on colour schemes?


Background

Measurement of colour distance:

my decision: CIEDE2000 formula (∆E00) more reliable than other formulas when applied to very small colour differences as

well as very large (Carter and Huertas, 2009) regarded as the best uniform colour-difference model (Yang et al., 2012)

216 web-safe colours in RGB model and transformed to CIELAB color space


Experimental Findings

based on results of experimental studies several findings about colour distance on sequential colour schemes were found

methods online questionnaires eye-tracking experiments

measured metrics accuracy response time eye-tracking metrics AOI analyses

conditions shades of green and red 6-classes colour schemes equal and unequal colour distance steps


#1

larger colour distance between classes is better, than smaller


#2

The minimal optimal value of colour distance between classes is ΔE00 = 4


#3

Equal colour distance steps between classes causes lower readability of ‘middle’ classes of the colour schemes


#4

‘Middle’ classes should be differentiated more, than ‘edge’ (min and max) classes



#5

Distinguishing the same colour distance is harder when there is a larger spatial distance between compared areas

< 1.5° 2.5 - 3.0° 6.0 - 7.5°


#6

The map reading task should be taken in the account while comparing values of two areas the user demands on colour distance

are smaller, than when determining the exact value of area by matching it with the legend

vs.


#6

The map reading task should be taken in the account while comparing values of two areas the user demands on colour distance

are smaller, than when determining the exact value of area by matching it with the legend


#7

even though the sensitivity of human eye varies across the visible spectrum the leading hue of the colour scheme should not influence the readability of map if the colour distance pattern is preserved.


Atlas of the Phenological Conditions in Czechia

8 colour schemes with 6 classes eye-tracking experiment 8 stimuli (phenophase maps) task: match the depicted area with the legend category

38 participants experimental design and analyses by A. Vávra and S. Popelka


Evaluation of Colour Schemes

How colour schemes of the Atlas match with my experimental findings?

(theoretical) colour distance between neighbouring categories CMYK sRGB primaries CIELAB CIEDE2000



#2: All measured colour distances between classes are larger or equal to the minimal optimal distance ΔE00 = 4.



#3: equal colour distance steps between classes cause lower readability, however colour distances between some classes do not vary enough



#4: Towards the centre of most of colour schemes colour distances decreases. This is especially apparent in the case of pink, orange, green and purple colour schemes.



Measured accuracy of answers



Conclusion

pink, green, purple (and orange) schemes seem to be sub-optimal (less than 60% (and 80%) accuracy)

but… for more precise results further in-depth investigation is

necessary …size and spatial distribution of areas, physiological and

mental aspects of the map user, simultaneous contrast were not taken into the account


Thank you for your attention…

Data & Analytics

Brychtova - Evaluation of colour schemes usability in Atlas of the Phenological Conditions in Czechia