ELECTREX
Background
Methodology
Dynamic Range
It is a ratio of the maximum measurable intensity to the minimum detectable intensity level
in scenes, images and display devices.
Method Selection
LDR Images
Wide Dynamic Range (WDR) Imaging
It is a solution for improving low dynamic range (LDR) images captured from scenes which
have both bright and dark areas. It is acquired especially when scenes of interest have wide
range of light intensity variations.
WDR Image Generation
WDR Image
Problem Statement
WDR Image Visualization
(Tone-Mapping)
LDR Image
Analysis
Range of luminance (or illuminance) measured in cd/m2 [8]
(Source: CambridgeInColor.com)
Objective
Computation Time
During image capture, dynamic range of original scene is reduced due to limited capability
of camera sensor to map all scene’s intensity levels. The reduction from wide dynamic
range to low dynamic range will cause some losses of image details.
Subjective
Observer Evaluation
Implemented Algorithms
Dynamic range of
original scene
WDR Image Generation: MATLAB function (“makehdr”)
Dynamic range of
captured image
Reduction of dynamic range of original scene during image capture
(Source: CambridgeInColor.com)
Image Generation
To solve the previous problem, one has to generate a WDR image which covers almost all
scene’s intensity levels. Therefore, losses of image details can be minimized.
WDR Image Visualization (Tone-Mapping): Logarithmic, Exponential, Reinhard et al (Global
Operator), Reinhard et al (Local Operator), and Garrett et al. Also, MATLAB function
(“tonemap”) and Photomatix (Details Enhancer and Tone Compressor) for comparison
purpose.
Results and Discussion
Output Images
Image Visualization
The generated WDR image will then have wider dynamic range. However, the conventional
LDR display devices like CRT and LCD have low dynamic range. Therefore, not all intensity
levels of WDR image can be displayed. To solve this problem, dynamic range of WDR
image must be scaled down so that it can be displayed properly on LDR display.
Objectives and Project Scopes
 To implement methods of WDR image generation
 To implement methods of WDR visualization or tone-mapping
 To analyze the output images resulted from the implemented WDR tone-mapping
methods through both objective and subjective measures
WDR Image Generation
It is a process of generating an image with wider dynamic range by combining LDR images
with different exposure settings to cover almost all scene’s intensity levels.
WDR Image
A: Logarithmic
B: Logarithmic
(Modified)
C: Exponential
(δ = 0.0001)
D: Exponential
(δ = 0.001)
E: Exponential
(δ = 0.01)
F: Exponential
(δ = 0.1)
G: Exponential
(Modified, δ =
0.0001)
H: Exponential
(Modified, δ =
0.001)
I: Exponential
(Modified, δ = 0.01)
J: Exponential
(Modified, δ = 0.1)
K: Reinhard et al
(Global Operator)
L: Reinhard et al
(Local Operator)
M: Garrett et al
N: MATLAB
O: Photomatix
(Details Enhancer)
P: Photomatix
(Tone Compressor)
Computation Time
The fastest: Logarithmic, Exponential and Reinhard
et al (Global Operator)
The slowest: Reinhard et al (Local Operator)
WDR Image Visualization (Tone-Mapping)
It is a process of compressing or scaling down the dynamic range of generated WDR image
so that it can be displayed properly on LDR display device.
WDR Image
NAME
ID NUMBER
SUPERVISOR
: WAZIRAH BINTI MD ESA
: 8998
: DR. AAMIR SAEED MALIK
SLOT NUMBER
: 66
Observer Evaluation
12 persons have evaluated all output images.
Rating scale is set between 1 (best) and 6 (worst).
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Algorithm
Reinhard et al (Local Operator)
Reinhard et al (Global Operator)
Photomatix (Tone Compressor)
Exponential (δ = 0.01)
Photomatix (Details Enhancer)
Exponential (δ = 0.001)
Exponential (δ = 0.0001)
Exponential (δ = 0.1)
Garrett et al
MATLAB (tonemap)
Exponential (Modified, δ = 0.1)
Exponential (Modified, δ = 0.01)
Logarithmic
Exponential (Modified, δ = 0.001)
Exponential (Modified, δ = 0.0001)
Logarithmic (Modified)
Overall Average Rating
2.41667
2.48810
2.65476
2.84524
2.95238
3.02381
3.05952
3.10714
3.38333
3.41667
4.03571
4.14286
4.63095
4.69048
4.80952
5.17857
Ranked algorithms according to their overall average rating.
Conclusion
 The computation time is affected by the algorithm complexity and the size of input
images used.
 Most people prefer output images with good visibility and color appearance.