Image Processing Reference
or some very rare live events on TV that are never going to be broadcast again are worth
encoding—even from a low-quality original.
Keep in mind that the lower the quality of the original, the worse it is going to look
after it has been encoded. You must be prepared to put in a lot of extra work and to be dis-
appointed in the results, at least on the first try.
Quadrature And Edits on VHS
The Phase Alternate Line (PAL) system depends on the correct phasing of the color infor-
mation with respect to a reference signal. When the video is recorded onto a VHS recorder,
the combination of PAL coding and the modulation of the signal onto the tape causes a
rotating phase relationship that takes 4 frames to cycle. It is like the cadence effect on
NTSC pulldown footage. You cannot cut with anything more reliable than a 4-frame accu-
racy in PAL on VHS. Footage that has been edited on VHS might have been done on a
4-head machine but at the edit point, there may still be synchronization irregularities.
These could cause some tearing of the video as it is ingested. You should carefully inspect
the footage if you think it has been edited in this way, and you might have to make some
remedial cuts to clean it up before compression.
Are Tapes Dead?
It might appear that tape formats are defunct and no longer of any use but they are still
useful because they are good for large, bulk storage at very cost-effective prices. Their
dominance in this area is being challenged by removable-disk formats and it will be inter-
esting to see the effects of second-generation DVD formats such as Blu-Ray when they
And Now for Something Completely Different
Let's now change direction completely and discuss some business and commercial issues,
some of which are sometimes uncomfortable to talk about. In the area of money, video
compression brings up some significant issues regarding the cost of using the technology
and the rights of consumers when they have access to the content. In the next chapter we
look at some of the challenges that DRM and intellectual property present to us.