[M4IF Technotes] Motion estimation + SAD

[Peter Haighton]

>Okay, I think I'm sorted now, but is the prediction error the absolute of
>the difference between current and previous frames?

No, the error is most definitely a signed value.
>If we only have 8 bits / pixel I was wondering what happens about the
sign
>and whether the DCT only worked with positive values.

The difference can be in the range (for 8 bit) of -255 to 255. Of course
how many bits you actually use to store this information is an
implementation issue.
>I'm assuming that the prediction error can be -ve otherwise the decoder
>won't know how to reconstruct the block., but I'm not sure how to handle
>the -ve sign.

That is correct, you must handle the sign. This is why SAD and calculating
the actual error are different things. SAD is a tool that helps find the
location with the smallest error. The smaller the error, the less bits to
encode.
Peter
--
Peter Haighton
VideoSpheres Inc.
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