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Here
are some pointers to relevant resources regarding Seam Carving, in addition
to the class lecture.
The original paper (http://doi.acm.org/10.1145/1276377.1276390)
gives the description of the dynamic programming approach and the particular
energies used.
The paper on video seam carving (http://doi.acm.org/10.1145/1360612.1360615)
has the derivation of the graph cut version of finding optimal seams as well
as the description of the forward energy.
The project pages by Ariel Shamir at http://www.faculty.idc.ac.il/arik/SCWeb/imret/index.html
and http://www.faculty.idc.ac.il/arik/SCWeb/vidret/index.html
are also worth checking out (nice image comparisons there for example).
In the first homework assignment (due Jan 13. at 8pm PST) we are asking you
to implement seam carving. Specifically your program should:
- read an image file
(either use some library that does this in some transparent way or limit
yourself to some easy [standard] file format)
- use the dynamic
programming approach to implement vertical seams only.
- use the e1 energy both
backward and forward versions (have some way of choosing which one so
that you can compare). To deal with color treat rgb as a 3-vector and
interpret |\partial_x I| as the l_2 norm of a 3-vector.
- in a preprocess
compute all seams to support a reduction by 0-50% of image width. Use
smart numbering of pixels (as described in the paper [or maybe something
better you come up with yourself?]) to support fast interactive window
resizing in the x direction after preprocessing is finished. Try to be
efficient about the preprocessing, but don't waste time getting super
tight in your code. This is not a speed competition, though having to
wait 4 minutes each time gets to be a drag...
- also do expansion up
to 50% doing the "run backwards and interpolate" idea
described in the paper.
- this rescaling should
be accomplished interactively by resizing the window on the x direction.
Extra bonus points:
- allow the user to
"draw" onto the image to indicate that some region should have
very low energy (to support something like the object removal trick
shown in the paper).
The bonus is 30%. Think carefully whether it's worth your time (if you
already have bits of code to get mouse input to draw some region, say
with a big disk, then do it; if you don't, you may well be spending too
much time just dealing with user interface issues to make this worth
your time...). There'll be other bonus assignments, so no need to grab
this one...
Collaboration policy:
- when trying to
understand the content of the papers, please work together; help each
other out!
- stop short of writing
code on the whiteboard since it is too easy for two people to end up
handing in what amounts to the same code, otherwise. That would not be
good.
In summary:
- discussion (and
generation!) of ideas together is GREAT! Implementation details everyone
has to sweat on their own.
For this particular assignment only:
- if you have a small
snippet of code that uses some image library to open an image file (say,
jpeg or tiff) and display it in a window, share this with the rest of
the class. Nobody should waste their time banging their head against the
wall on that part.
What you need to hand in (to Mathieu by 8pm PST Jan 13)
- a pointer to a simple
web page showing the results of running your program on 3 different
images. Consider using images from the paper, which you can download
from the above web page pointers. Show a comparison of forward and
backward energy. Show at least one example where the image content is
such that things don't work very well.
- have a link on that
page to your code and executable (separate links). If you use a different
OS than Windows XP to make your executable, tell me where in the
building I can run your code. If it's something exotic, talk to me ahead
of time so we can address the "where do I run this program"
issue ahead of time. Needless to say I will also need to know how to
invoke your program (command line options? user interface? mouse click?
keyboard?). This should be documented on the above web page.
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