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are the same, than algorithm has medical value. Result must be 100 %
unchanged if the original can be destroyed. In that case, saving of storage
space can be achieved.
Step 8. In this step, shadows are detected and emphasize with pointing color to
make diagnostics easier. Shadows are detected by histogram method. In
the method, suspicious pixels are detected by colors of asbestos shadows.
It is easy said that suspicious colors will be painted differently. However,
histograms depend on many factors, which are not necessarily the same.
Therefore, suspicious colors can be different on different X-ray machines.
Even if the machinery is the same, if there is no direct digital transfer of
image, scanning process can be different and produce different histogram.
That is the reason why automatic detection of asbestos shadows should be
avoided. It is better that human picks suspicious color and then algorithm
emphasizes chosen color in the image of the lung. Based on the research
on, approximately, 200 real patients, we determined critical colors.
However, it does not mean for sure that it works everywhere. This is the
reason to choose manual selection of colors. With this selection, color
renormalization is performed and new adopted histogram is obtained.
Implementation of the wavelet transform depends on the programmer's choice:
it can be classic filter implementation or lifting. Lifting algorithm is faster and the
results are the same as corresponding filters.
6.4 Results
In this section, some of results are presented in area of compression and medical
fidelity.
Since there were a lot of discussion in scientific community about image for-
mat, which can be allowed for medical imaging, it can be concluded that the safest
way is to use formats which does not change original data in any way (i.e., bitmap
maps every pixel). If original data is processed in some sort of coding (maybe with
some threshold), risk of losing data exists, because some medically important
detail can be lost.
Except image format, other questions came up as well, i.e., gray image versus
color or which resolution is satisfactory. According to DICOM (eng. The Digital
Imaging and Communications in Medicine) standard, minimal resolution for
medical images should be 300 dpi [ 26 ]. Except bitmaps and tiff format, JPEG was
tested in the research. JPEG images were compressed to size of approximately
350 KB. Original images take around 4.5 MB. Therefore, compression ratio (CR)
for analyzed images in JPEG format is:
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