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ige around skin 
  
  
(a) (b) 
Figure 4. Homomorphic filter applied to test image#l (a) 
Original Test Image£1 (b) Homomorphic Filtered Image: RGB 
strength 1.50 
Different strength conditions were tested and it was decided 
there is no significant difference between values of 1.50 to 2.00, 
on the other hand RGB and Luminance condition used during 
the filter reveals different effects. Luminance provides closer 
visualization to the original image but using RGB values 
applies biggest contrast around the disorder area. Thus, it is 
considered that this enables to discriminate the differences 
between the scar and the normal skin more easily. 
As a second consideration of criteria, exposure compensations 
were tested and homomorphic filter was also applied to them. 
As a result of the comparison, changing exposure levels does 
not affect images dramatically especially after applying the 
homomorphic filter. 
5. REGISTRATION 
Evaluation of the disease, growth or reduce of its size can be 
detected only if they are both in the same coordinate system. In 
order to provide the same coordinate system for both images 
“image to image” registration needs to be applied. In order to be 
able to perform arithmetic (and other comparing) operations 
between the pixels in two images, there should be available an 
automatic process to refer them in the same ground space. The 
solution to this problem lies beyond the targets of the current 
work and a generic settlement is not provided. There are many 
algorithms that might be used to perform a registration between 
images. The most commonly used is the SIFT (Scale Invariant 
Feature Transform) and its variation that has been used with 
great success in the creation of panoramic images. For more 
details please follow the references (Lowe, Meng). However, in 
the current study a couple of time variant images should be 
referred to each other, thus they were registered manually using 
the Autodesk® Raster Design software. The software is freely 
available to all the academic higher educational institutes 
(http://students.autodesk.com) and the latest version 2010 has 
been used. During the registration process, the one of the 
images is left unchanged while the other is aligned using a 
triplet of very well defined points visible also to the original 
one. The scale, shift and rotation of the second image are 
applied and a resampled image is generated. A common 
rectangle area is used to crop the two images in the same 
ground space (using the same ground resolution) and the 
comparing algorithms are applied to extract the healing progress 
of the tissue. 
6. IMAGE PROCESSING BY FILTERS 
As a main purpose of the project, skin disorders, basically scars 
are tried to be extracted automatically from healthy skin and 
observe their evaluation if they are growing or healing by using 
some filters. For this aim, the best visualization is considered to 
be black and white images. Adobe Photoshop 7.0 was used as 
image processing software. All the filters were applied on both 
homomorphicaly filtered “Test Image#1” and “Test Image#2” 
6.1 Photocopy — Trace Contour 
Photocopy filter, which is under the Sketch section in 
Photoshop Menu tend to copy large areas of darkness on the 
original image around the edges and the other areas are drawn 
back to either solid black or white (Adobe Photoshop Help 
Center). Photocopy filter has two criteria these are detail and 
darkness. Detail refers to how much detail in the original image 
will be filtered while darkness refers to how dark the details will 
be (Yousif, 2005). 
Trace Contour filter that lies under “Stylize” section in 
Photoshop Menu uses transitions of major brightness areas in 
image and highlights them in order to produce lines similar to 
contours in a map. This filter has two settings, edge option and 
level. In Edge Option, lower edge outlines areas where the color 
values of pixels fall below the specified level and upper edge 
outlines areas where the color values fall above (Adobe 
Photoshop Help Center). Level can take a value between 0 and 
255 and it indicates the threshold for the evaluation of tonal 
values in the image. 
Multiple tests were run with different detail/darkness values and 
with different edge option/level values. 
  
  
  
  
  
  
  
  
(a) (b) (c) 
Figure 5. Homomorphicaly Filtered Test Image#1 (a) 
Photocopy filter (Det: 24, dark:5) (b) Trace Cont. (Level, Edge 
Lower:128) (c) overlay with original image 
  
   
  
  
  
  
  
  
  
(a) (b) (c) 
Figure 6. Homomorphicaly Filtered Test Image#1 (a) 
Photocopy filter (Det: 24, dark:10) (b) Trace Cont. (Level, Edge 
Lower:170) (c) overlay with original image 
6.2 Photocopy — Threshold 
Threshold level defines the value that all the pixels lower than 
this value are converted to black colour and all pixels higher 
than threshold are converted to white colour. The value of 
threshold level is inversely proportional to the darkness as the 
parameter of photocopy filter (Adobe Photoshop Help Center). 
  
   
  
  
  
  
  
  
  
(a) (b) (c) 
Figure 7. Homomorphicaly Filtered Test Image#1 (a) 
Photocopy filter (Det: 24, dark:5) (b) Threshold (Level:128) (c) 
overlay with original image