Re: Image Delta Compression

"Colin Andrew Percival" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
>   Where do the images come from?  Is there entropy in the low order bits
> (eg, from physical inputs)?  Do "moving parts" always move by unit numbers
> of pixels?  Does a large proportion of the image remain fixed, or could
> everything be offset by (for example) 1.3 pixels in one image?

Colin,

sorry, I was so lost in my little world that I forgot to provide the big
picture. There's little to no entropy in the low-order bits and moving parts
move by one or more pixels.

A good analogy would be screenshots: let's say you're writing an email and
you take screenshot, then take another one in 30 seconds. The difference
would usually be very small - only a few lines added, and no parts of the
image would move. However, you could also scroll the contents of the email
by two lines up between the two screenshots, in which case you'd have a fair
amount of movement to handle. Or you could drag the window you're writing
the email in 5 pixels up and 10 to the left - again, motion to detect.

As I wrote, my initial approach - the generic binary diff - produces a
pretty small delta output when working with small string lengths, but the
time it takes to do so is way too long.

Marton