They use some terms like DC(or TF) without explaining what they mean. I could not understand them without significant effort.
For example, for "DC" I know(after careful analysis) that they mean constant average value, it could mean Discrete Cosine, or Discrete Component. What does it mean? "Direct current"?
How Direct current will make any sense in a digital signal article?
The term originated in electronics, where it refers to a
direct current voltage, but the concept has been extended
to any representation of a waveform. The term's use is
extended to two-dimensional transformations like the
discrete cosine transform used in JPEG.