AMV Post Production - Resizing
This is the last stage of the post-production process. With
any luck you'll have an avisynth script that imports your exported avi,
deinterlaced (if required) and filtered.
Now it's time to choose your resolution. First off, if you
edited something that's a movie and was letterboxed, you may want to
crop out any black bars it has before encoding it for the internet. You
may also want to crop off any unwanted borders that a source may have
as this can hurt compressibility.
Mostly, you won't need to crop for convention encodes as they
are likely to need DVD resolution. However you can always crop and then
add the same amount of black border in order to clean up any nasty
edges your source may have.
I would suggest opening up your script in VirtualDubMod, going
Video->Filters->Add->null transform and then clicking the
"Cropping button" to bring up the cropping screen. This will give you a
nice GUI with which you can figure out how much you need to crop. Write
down the values and then add the following line to your AVISynth script:
where the 4 values there are the number of pixels you're
cropping off from each edge. Note that you want to make the last two
numbers negative! If you don't, it interprets the last two numbers as
being destination resolutions, for instance the following lines
performed on a 720x480 clip:
will both produce the same result, however the first syntax is
easier to read and corresponds to the values you can see in
VirtualDubMod's cropping GUI.
What size to choose
This all depends on your distribution. However, there is one
universal piece of knowledge you need - many codecs will make bad
encodes unless your resolution is a multiple of 16.
For 4:3 encodes, choose between 320x240, 480x352,
512x384 and 640x480. Higher is better quality but larger filesize. I
tend to use 512x384 unless the source is very compressible (or I want
to show off the quality) in which case I will make a 640x480 encode.
For 16:9 encodes, choose between 480x256, 512x288
and 640x352. Notice that not all these resolutions are exactly 16:9 -
this is because of the need to create multiples of 16. The aspect ratio
difference is small, however.
For 4:3 NTSC encodes you should choose 720x480
For 4:3 PAL encodes you should chooose 720x576
For 16:9 encodes you should always convert your
footage to a letterbox format. For NTSC, first resize to 640x360
and then use Addborders(0,60,0,60). For PAL footage first resize to
720,432 and then use AddBorders(0,72,0,72).
Now you should decide which resizing method to use. There are
three different algorithms you can use: BilinearResize, BicubicResize
and finally LanczosResize. They differ in how sharp
the image is when resized. Sharper is much better quality visually but
it is also harder to compress so you need to balance the sharpness with
the final file size you want. However, a less sharp resize can hide
imperfections in the video.
BilinearResize will give you smaller filesizes and on
older anime that was shot on Film it is most likely the better choice.
It does a little blurring so this makes it the ideal choice if you want
to get as small an avi file as possible. If (like me) you find Bilinear
to be too blurry, then you'll want to choose something sharper...
BicubicResize actually comes in various forms as you
can specify the amount of sharpening performed. The most common
varieties of Bicubic are Soft, Natural and Sharp. Soft Bicubic is
sharper than bilinear but not as costly to compression as Neutral or
Sharp Bicubic. Of course, if you want and even clearer sharper picture
then Lanczos is the algorithm you want.
LanczosResize - excellent detail, but the sharpness
comes at a price in terms of compressibility. However, with some
filtering on your amv they can nicely balance each other out - I
frequently use this option on my music videos after filtering to get
really clean encodes. This is not always recommended for internet file
encoding (without filtering at least) but great for other purposes
(like resizing for cons etc). In fact there is an even more accurate
version of this called Lanczos4Resize which you can use for
To perform a Bilinear resize, add the following line to your
avisynth script, replacing "width" and "height" with the numbers you
For a softer Bicubic, add:
The last two parameters are changing the strength of the algorithm and
what give it its "softer" touch. Normal Bicubic is 0.75 and produces a
much sharper, more difficult to compress picture.
So, to resize your video to 480x352 using the soft bicubic
method, add this line:
If you're encoding to DVD-quality MPEG2, you'll want your
resize to be a precise as it can be so use
Lanczos4resize will not be detected by VirtualDubMod, but it
should work well.
Personally I use the regular LanczosResize command even on my
internet distributions as it doesn't hurt compressiblity that much
provided you have filtered the footage beforehand. Give the different
resizers a try and see what suits you.
Adding Black Bars
Don't forget that if you are letterboxing your video for a convention
then you will need to add borders after your resize, like so:
Remember: Resizing like this should only be done
on PROGRESSIVE footage. If you want to resize interlaced
footage you either have to limit your resizing to being horizontal or
you have to separate the fields, resize those and then weave them
together. Here's an example script for letterboxing an interlaced
Notice that the vertical resoluton
on the resize is half what it would normally be - this is
because we are resizing one field at a time. When the fields
are re-combined with Weave() the frame will have the correct size.