Evolving art using measures for symmetry, compositional

balance and liveliness

Eelco den HeijerVrije Universiteit Amsterdam

Outline• Introduction

• Symmetry

• Compositional balance

• Liveliness

• Experiments & Results

• Conclusions

• Future work

Introduction

• Unsupervised evolutionary art

• No human in the loop

• Aesthetic Measures

• fitness functions, computational aesthetics

• impact on `style’ of resulting image

• Global Contrast Factor, Ralph/ Ross Bell curve, Machado/ Cardoso, Benford Law

Symmetry & Balance• Symmetry

• Ubiquitous - it’s everywhere...

• Important in design, architecture

• ‘Hard-wired’ in human visual system?

• It’s role in visual art is not straightforward

• Compositional Balance

• Important in graphic design & visual art

• Processing fluency (Reber)

Motivation• Evo* paper 2011

• Multi-Objective Evolutionary art

• Multiple aesthetic measures

• Some combinations work well, some combinations do not (same `dimension’, opposing directions)

• Need for aesthetic measures that work on other ‘dimensions’ (e.g. symmetry)

Research Questions

When using unsupervised evolution (i.e. without a human in the loop);

1.Is it possible to evolve symmetric images?

2.Is it possible to evolve `balanced’ images?

3.Do the aesthetic measures for symmetry and balance mix well with other aesthetic measures?

Related work (1)• Several aesthetic measures in unsupervised

evolutionary art

• Machado & Cardoso (1998)

• Image complexity & Processing complexity

• Matkovic et al (2005)

• Global Constrast Factor

• Ross & Ralph (2006)

• Bell curve

• Several others

Related work (2)

• Ngo et al (2000)

• Symmetry in GUI screens

• Bauerly and Liu (2005, 2008)

• Aethetic evaluation of symmetry in web pages

Calculating Symmetry• Select two areas (depending on orientation)

• Mirror the second area (using the proper axis)

• Calculate difference in intensity values between all pixels in the two areas

• If difference is below 0.05 diff=1, else diff=0

Symmetry? Relax...• Is too much symmetry a good thing?

• Finding a `sweet spot’ for symmetry

• We did not find a value for this `sweet spot’ in literature

• we used 0.8 in our experiments

Compositional balance• Compute visual similarity (or distance) between

image regions

• Stricker & Orengo image distance function (1995)

• Image is `compressed’ to a feature vector

Stricker & Orengo

Calculating Balance

• Select two areas (depending on symmetry type)

• Determine feature vector for both areas

• Calculate Stricker & Orengo difference

Liveliness• Using only symmetry would lead to a lot of

monochrome images (since they are perfectly symmetrical...)

• Same goes for compositional balance; two halves of a monochrome image have identical feature vectors

• So, we need additional constraints

• Not only symmetrical, but ‘lively’ too

Liveliness: how?• A simple and naive measure for ‘interestingness’

• Our definition;interestingness = ‘having a high distribution of intensity values’

• Calculate entropy of intensity values (x=intensity value):

Experiments

• Unsupervised

• No humans...

• Genetic programming

• `Pixel paradigm’

Experiment Setup

1 Symmetry (bilateral) (+ liveliness)

2 Relaxed symmetry (+ liveliness)

3 Compositional balance (+ liveliness)

4 Multi-objective (NSGA-II); a) Symmetry (all directions)b) livelinessc) Global Contrast Factor

1. Bilateral symmetry

2. Bilateral symmetry (relaxed)

3. Compositional Balance

4.Combination (GCF + L + Sym)

Conclusions (1)• Our evolutionary art system has no

difficulty in evolving symmetric images

• Relatively `easy’ aesthetic measure (rapid fitness progression)

Conclusions (2)• It is possible to control the `amount’ of

symmetry in an unsupervised evolutionary art system

• Compositional balance

• Images often ‘just‘ symmetrical

• Might need additional ‘penalty’

Future work• Other distance functions for compositional

balance (e.g. based on texture)

• Experiments with symmetry using different representations (e.g. SVG)

• Good test for compositional balance measure

• Improve compositional balance measure

• Detect blobs, determine their weight, etc.

Thank you!Images and papers at

http://www.few.vu.nl/~eelco Questions?

eelcodenheijer@gmail.com