Perceptually Based Depth-Ordering

Enhancement for Direct Volume Rendering Lin Zheng, Yingcai Wu, and Kwan-Liu Ma

VIDI Research Group, UC Davis

Introduction

• Depth Perception: • visual ability to perceive the distance of 3D objects.

• Depth cues

Binocular CuesMonocular Cues

Occlusions Size Shading Stereopsis Disparity

Introduction

• In many visualizations, the depth ordering is ambiguous.• If there is no interaction:• static images on the magazine• posters

• Possible approaches:• Perspective projection• Halos, shadows, warm/cool color

Neghip

Related Work: Halos

• Enhancing Depth-Perception with Flexible Volumetric Halos, Stefan Bruckner and M. Eduard Gröller, 2007

• Depth-Dependent Halos: Illustrative Rendering of Dense Line Data, MH Evert and etc., 2009

Related Work: Warm/Cool Color

• Color Design for Illustrative Visualization, L. Wang, J. Giesen, K.T. McDonnell, P. Zolliker, and K. Mueller, 2008

Perception Models

• Only change the inherent factors: Luminance, opacity• We introduce two major models for depth perception:• X-junction Model• Transmittance Anchoring Principle (TAP)

• X-junction Model has limitation• TAP can be a complement

X-Junction Model: C-configuration

• Which layer is in the front• A or B?• Luminance(s)• > Luminance (r)• > Luminance (p)• > Luminance (q)• The luminance

decreasing in a “C” configuration.

X-Junction Model: A-configuration

• Which layer is in the front• Luminance (r) = (q)• The Luminance decreasing

order can be s>r=q>p• Or s>q=r>p• A-ambiguity

X-Junction Model: Z-configuration

• Luminance s>r>q>p• The luminance decreasing

in a “Z”-configuration• Still ambiguous?• + TAP model

Application of Perception Models

• TAP: the highest contrast is perceived to be at the background• Applying X-junction Model and TAP Model.• Improve A-ambiguity to Z-configuration, then to C-configuration

Z-configuration C-configurationA-ambiguity

Energy Function Design

• Three terms :

• Enhance the Perceived Depth Ordering• Keep the Perceived Transparency• Keep the Image Faithfulness

depth ordering transparency image faithfulness

Energy Function Design

• Perceived Depth Ordering:configuration of the junction area• Wrong C-configuration will not appear in semi-transparent structure• Four configurations (in DVR):• Wrong Z-configurations

• A configuration (A-ambiguity)

• Correct Z-configuration

• Correct C-configuration

Energy Function Design

• Perceived Transparency:

Metelli’s episcotister modelLuminance of transparent layers

Information EntropyConditional entropy

• Image Faithfulness:

Optimization

NO

Optimal

User Study

• Design:• A between-subjects study (12 subjects)• 60 cases total: 30 enhanced and 30 original

• Fisher’s exact test• Users were significantly more accurate in

enhanced cases: P-value = 0.0016

task interface

Results: neghip

• Although the difference is subtle, our user study shows that enhancement improves depth perception significantly

initial enhanced

Results: neghip

initial enhanced

Results: neghip

initial enhanced

Results: vortex dataset

initial enhanced

Results initial enhanced

Discussion

• + Easy to be embedded in current visualization system• + Luminance as the visual cue:• a primary visual cue in visual psychology• does not introduce additional overhead

• - Limitations of perception models:• deal with two overlapping layers at a time• do not work for enclosing and separate structures• consistency problem with intertwined structures

Conclusion and Future Work

• Investigated how to perceptually enhance depth ordering• Used perception models for quantitative measurement• Depth ordering (X-junction Model, TAP)• Image quality (Metelli episcotic Model)

• Designed an optimization framework for enhancing depth perception

• Conducted a user study showing the effectiveness of our approach• Future work: animation

Thank you!

• This research has been sponsored in part by the US National Science Foundation (NSF) through grant CCF-0811422 and US Department of Energy (DOE) with award DE-SC0002289.