2. Introduction
• Developments in the field of sensing
technology
• Multi-sensor systems in many applications
such as remote sensing , medical imaging ,
military , etc.
• Result is increase of data available
• Can we reduce increasing volume of
information simultaneously extracting all
useful information
3. Basics of image fusion
Aim of image fusion is to
• Reduce amount of data
• Retain important information and
• Create new image that is more suitable for
the purposes of human/machine perception
or for further processing tasks.
4. Single Sensor image fusion system
• Sequence of images are taken by the sensor
• Then they are fused in an image
• It has some limitations due to capability of
sensor
5. Multi-sensor image fusion
• Images are taken by more than one sensor
• Then they are fused in an image
• It overcomes limitations of single sensor
system
7. DARPA Unveils Gigapixel Camera
• The gigapixel camera, in a
manner similar to a parallel-
processor supercomputer,
uses between 100 and 150
micro cameras to build a
wide-field panoramic
image. These small
cameras' local aberration
and focus provide extremely
high resolutions, combined
with smaller system volume
and less distortion than
traditional wide-field lens
systems.
12. System level consideration
• Three key non-fusion processes:
• Image registration
• Image pre-processing
• Image post-processing
13. • Post processing stage depends on the type of
display, fusion system is being used and the
personal preference of a human operator
• Pre-processing makes images best suited for
fusion algorithm
• Image registration is the process of aligning
images so that their detail overlap accurately.
14. Methodology
Feature detection
• Algorithm should be able to detect the same
features
• Feature matching
Correspondence between the features
detected in the sensed image and those
detected in the reference image is established
Image resampling and transformation The
sensed image is transformed
16. Weighted pixel averaging
• Simplest image fusion technique
• F(x,y)=Wa*A(x,y)+Wb*B(x,y)
• Where Wa, Wb are scalars
• It has an advantage of suppressing any noise in
the source imagery.
• It also suppresses salient image
features,inevitably producing a low contrast
fused image with a ‘washed-out’ appearance.
17. Pyramidal method
• Produce sharp , high-contrast images that are
clearly more appealing and have greater
information content than simpler ratio-based
schemes.
• Image pyramid is essentially a data structure
consisting of a series of low-pass or band-pass
copies of an image, each representing pattern
information of a different scale.
19. Discrete wavelet transform method
• It represents any arbitrary function x(t) as a
superposition of a set of such wavelets or
basis functions –mother wavelet by dilation or
contractions (scaling) and translational (shifts)
20.
21. Medical image fusion
• Helps physicians to extract features from
multi-modal images.
• Two types- structural (MRI, CT) & functional
(PET, SPECT)
22. Objectives of image fusion in remote
sensing
• Improve the spatial resolution
• Improve the geometric precision
• Enhanced the capabilities of feature display
• Improve classification accuracy
• Enhance the capability of change detection.
• Replace or repair the defect of image data.
• Enhance the visual interpretation.
23. Dual resolution images in satellites
Several commercial earth observation satellites carry
dual-resolution sensors of this kind, which provide
high-resolution panchromatic images (HRPIs) and low-
resolution multispectral images (LRMIs).
For example, the first commercial high-resolution
satellite, IKONOS, launched on September 24, 1999,
produces 1-m HRPIs and 4-m LRMIs.
24. PRINCIPLES OF SEVERAL EXISTING
IMAGE FUSION METHODS USED IN REMOTE SENSING
Multi resolution Analysis-Based Intensity
Modulation
À Trous Algorithm-Based Wavelet Transform
Principal Component Analysis
High-Pass Modulation
High-Pass Filtering
Brovey Transform
IHS Transform
26. each low-resolution pixel value (or
radiance) can be treated as a weighted average
of high-resolution pixel values
27. Brovey transform
.The BT is based on the chromaticity transform
It is a simple method for combining data from different sensors,
with the limitation that only three bands are involved. Its
purpose is to normalize the three multispectral bands used for
RGB display and to multiply the result by any other desired data
to add the intensity or brightness component to the image.
28. IHS Transform
The IHS technique is a standard procedure in image fusion, with the
major limitation that only three bands are involved . Originally, it was
based on the RGB true color space.
29.
30. High-Pass Filtering
The principle of HPF is to add the high-frequency information
from the HRPI to the LRMIs to get the HRMIs .
The high-frequency information is computed by filtering the
HRPI with a high-pass filter or taking the original HRPI and
subtracting the LRPI, which is the low-pass filtered HRPI. This
method preserves a high percentage of the spectral characteristics,
since the spatial information is associated with the high-frequency
information of the HRMIs, which is from the HRPI, and
the spectral information is associated with the low-frequency information of the HRMIs, which is
from the LRMIs. The mathematical model is
31. High-Pass Modulation
The principle of HPM is to transfer the high-
frequency information
of the HRMI to the LRMIs, with modulation
coefficients , which equal the ratio between the
LRMIs and the LRPI . The LRPI is obtained by low-
pass filtering the HRPI. The equivalent
mathematical model is
32. Principal Component Analysis
The PCA method is similar to the IHS method, with the main
advantage that an arbitrary number of bands can be used .
The input LRMIs are first transformed into the same
number of uncorrelated principal components.
Then, similar to the IHS method, the first principal
component (PC1) is replaced by the HRPI, which is first
stretched to have the same mean and variance as PC1. As a
last step, the HRMIs are determined by performing the
inverse PCA transform.
35. À Trous Algorithm-Based Wavelet
Transform
It is based on wavelet transform and is particularly suitable for signal processing since
it is isotropic and shift-invariant and does not create artifacts when used in image
processing. Its application to image fusion is reported in and .
The ATW method is given by
36. Multiresolution Analysis-Based
Intensity Modulation
MRAIM was proposed by Wang. It follows the
GIF method, with the major advantage that it
can be used for the fusion case in which the
ratio is an arbitrary integer M , with a very
simple scheme. The mathematical model is
37.
38. Comparisons
1-The IHS, BT, and PCA methods use a linear combination of
the LRMIs to compute the LRPIs, with different coefficients.
2- The HPF, HPM, ATW, and MRAIM methods compute the
LRPIs by low-pass filtering the original HRPI with different
filters.
3- The BT, HPM, and MRAIM methods use the modulation
coefficients as the ratios between the LRMIs and the LRPI,
whereas the IHS, HPF, ATW, and PCA methods simplify the
modulation coefficients to constant values for all pixels of
each band.
39. It is obvious that the IHS
and PCA methods belong to class 1, the BT
method belongs to class 2, the HPF and ATW
methods belong to class 3, and the HPM and
MRAIM methods belong to class 4. The
performance of each image fusion method is
determined by two factors: how the LRPI is
computed and how the modulation coefficients
are defined.
40. EXPERIMENTS AND RESULTS
1-The IHS and BT can only have 3 bands.
2-In order to evaluate the NIR band as well, we
selected the red–green–blue combination for
true natural color and the NIR–red–green
combination for false color
3-In comparison the NIR can be used with other
components of red,green and blue.
47. 4-MRAIM looks better than the other methods.
5-MRAIM looks better than HPM method in
spatial quality.
6-the correlation coefficient (CC) is the most
popular similarity metric in image fusion .
However, CC is insensitive to a constant gain and
bias between two images and does not allow
subtle discrimination of possible fusion artifacts.
48. Recently, a universal image quality index
(UIQI) has been used to measure the
similarity between two images. In this
experiment, we used the UIQI to measure
similarity.
The UIQI is designed by modeling any image
distortion as a combination of three factors:
loss of correlation, radiometric distortion, and
contrast distortion. It is defined as follows:
49. UIQI MEASUREMENT OF SIMILARITY BETWEEN THE DEGRADED FUSED
IMAGE AND THE ORIGINAL IMAGE AT 4-m RESOLUTION LEVEL
50. UIQIS FOR THE RESULTANT IMAGES AND THE ORIGINAL
LRMIS AT 4 m. (FUSION AT THE INFERIOR LEVEL)
51. This maybe because all the methods provide
good results in the NIR band, so the difference is
very small , while the spatial degradation
process will influence the final result differently
for different fusion methods.
52. Subscenes of the original LRMIs and the fused resulting HRMIs by different methods
(double zoom). (Left to right sequence, row by row) Original
LRMIs, IHS, BT, PCA, HPF, HPM, ATW, and MRAIM.
53. Conclusion
The performance of each method is determined by two factors: how
the LRPI is computed and how the modulation coefficients are
defined. If the LRPI is approximated from the LRMIs, it usually has a
weak correlation with the HRPI, leading to color distortion in the
fused image. If the LRPI is a low-pass filtered HRPI, it usually shows
less spectral distortion.
By combination of the visual inspection results and the quantitative
results, it is possible to see that the experimental results are in
conformity with the theoretical analysis and that the MRAIM
method produces the synthesized images closest to those the
corresponding multi sensors would observe at the high-resolution
level.
