Figure 3. A rejected over exposed X-ray 
  
Figure 4. A rejected under exposed X-ray 
THE PROPOSED SYSTEM 
Following is one possible solution to minimize the number 
of the rejected X-rays. The heart of the solution is the 
concept of image processing. All X-rays can be converted 
to digital images by simple or advanced scanning 
techniques. Once a digitized X-ray is obtained basic and 
advanced image processing techniques can be applied to it. 
Research shows that more than 90% of the rejected images 
are due to over- or under-exposure or to poor contrast in 
the obtained radiographs. Less than 10% of the X-rays are 
rejected because of the patient moving. In these cases 
image restoration and enhancements can be applied to 
minimize and/or correct the problem. 
The proposed system (figure 5) is nothing more than a 
typical image processing unit connected to an X-ray 
machine. 
Six rejected X-ray pictures were selected and then were 
digitized at different resolutions ranging from 50 to 300 um 
pixel size. Initial statistics were collected to select proper 
restoration techniques. Spectral and spatial image 
enhancement techniques were applied to the digital image. 
  
processor 
  
  
  
Display 
  
  
  
  
  
Figure 5. The Propose System 
Results show that linear and non-linear contrast 
enhancements increased the visual quality of the images 
and in many cases the new image is no longer classified as 
arejected X-ray. Spatial enhancement has the effect of 
bringing up the details of the image. Logarithmic and 
exponential histogram equalization gave good results in 
most cases. A combination of linear stretch and histogram 
equalization also proved to be effective enhancement 
techniques. High boost filter with central kernel value less 
than 10 gave the best result in most cases. High-frequency 
emphasis filter also proved to be a powerful tool for spatial 
enhancements. Different edge enhancement filters were 
examined and directional and Sobel filter worked the best. 
Figures 6, 7, 8 and 9 show some of the obtained results. 
These figures demonstrates that indeed a good part of the 
rejected X-rays can be retrieved. This process not only 
reduces number of rejected X-rays, but it also increases the 
quality of both the rejected and the good X-rays. The new 
obtained X-ray is sharper and more visually interpretable. 
The procedure will save both patient and physician time 
and money and will be much safer than the present day 
system. 
  
Figure 6. Exponential equalization for the 
X-ray in figure 3 
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