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

EVALUATION OF COLOUR SCHEMES USABILITY
of the Atlas of Phenological Conditions in Czechia
This presentation is co-financed by the
European Social Fund and the state
budget of the Czech Republic.
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:
216 web-safe colours in RGB model and transformed to CIELAB color space
my decision: CIEDE2000 formula (ΔE00)
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)

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…

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

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