Digital Signal Processing Reference
In-Depth Information
Figure 16.3. Examples of median
lter area.
Removal of salt-and-pepper noise also has a beneficial effect
upon subsequent video compression. This type of noise creates
high frequency, which needs to be encoded using high-frequency
DCT coefficients, requiring portions of the compressed bit-
stream to be wasted in representing this noise.
16.2 Mosquito Noise
Video compression and decompression can result in other
types of video distortion or artifacts. One common distortion
happens near sharp or crisp edges of objects in MPEG and other
video frames that use the discrete cosine transform (DCT). It
occurs during decompression when the decoding engine has to
approximate the discarded data by inverting the transform
model. Known as mosquito noise, it manifests as random aliasing
in these areas and appears as ringing around sharp edges. It is
caused by the removal of high-frequency coefficients during
compression quantization, as shown in
Figure 16.4
. As TVs and
monitors get larger, mosquito noise and other artifacts become
more prominent.
From EETimes
article “Video
compression
artifacts and
MPEG noise
reduction article”
by Algolith, 2006
Figure 16.4. Mosquito noise
example.
