The main aim of image sharpening is to highlight the fine details in an image or to enhance the blurred details (due to noise or other effects such as motion). It enhances the high-frequency components which use a spatial filter that has a high positive component at the center.
A simple 3×3 spatial filter that achieves image sharpening is
depicted in Fig.
High Boost Filtering
The high pass filtering is achieved by subtracting a low pass image
from the original image.
However, in many cases, a high pass image is required, where some of the low-frequency components are to be retained to enhance the interpretation of the image. When the original image is multiplied by an amplification factor ‘A’ before subtracting the low pass image,
a high boost or high-frequency emphasis filter is formed. Thus,
If A = 1, it is a simple high pass filter. When A > 1, only a part of the original image is retained in the output.
A simple filter for high boost filtering is illustrated in Fig.