What the heck?
525/59.94 DV and DVCAM uses 4:1:1 chroma subsampling. The coarse chroma
resolution causes all sorts of steppy edge problems in chroma keying
and in "upconversion" to 4:2:2 or 4:4:4 output formats.
Some DV codecs, like Avid's, filter or smooth the chroma on
decompression (details here
Matrox's, let you turn chroma filtering and interpolation
on or off as you see fit. But the Apple codec used in Final Cut Pro
doesn't give you any choice: it's steppy edges, all the way.
I got tired of trying to fix the problem with the matte chokers, so I
wrote FXScripts for (a) a chroma blur and (b) a Y/C offset, to
make keying easier and better, and to improve the quality of still
frames I pull from DV footage in FCP. And then later on I wrote some
more. And here they are.
They're free. Download them here
- Channel Balance - adjust the gain and level of
RGB or YCrCb (YUV) channels independently.
- Channel Blur - selectively blur RGB or YCrCb
channels independently. If you select YCrCb, and blur Cr and Cb about
2-4 units, it makes a passable-fair chroma smoother for 4:2:0
- Channel Offset - tweak the positions of RGBA or
YCrCbA channels independently. In YCrCb mode, it’s useful for shifting
chroma to correct for multiple generations of analog, color-under
- Field Balance - adjust luma and chroma gains on
Fields 1 and 2 of an interlaced image independently. Very useful for
correcting field imbalances caused by mismatched head amps in
dual-head, helical-scan analog VTRs.
- H. Chroma Blur - an alternative to FCP’s own
4:1:1 and 4:2:2 chroma smoothers (and predating them, grin), this lets
you adjust the horizontal blurring and offsetting of the chroma signal
to correct for color-subsampled recording formats like DV. Sometimes
Apple's filters work better. Sometimes mine do.
- Pixel Mask - Hide a dead or hot pixel (and its
surrounding compression artifacts, if necessary) with a mask made from
adjacent pixels. Read this
article for details on Pixel Mask, and on how to write your own
- Y/C Delay - this is a streamlined version of
Channel Offset: it just repositions chroma with respect to luma so that
colors that have shifted from too many generations of color-under
recording can get put back where they belong. It can also be useful in
repositioning subsampled chroma for cutting a key with; sometimes a
slight leftwards (negative number) offset makes for a better-aligned
them and unzip them; you’ll get a folder called “AJW’s Filters”.
Drop it into /Library/Application
Cut Pro System Support/Plugins. Start (or
restart) FCP. Hey presto: new filters!
Use them, take them apart, rebuild them, modify them for your own
nefarious needs based on your own brilliant brainstorms. Throw some or
all of them away if they bore you. That’s freedom, isn’t it?
Note: these filters are provided
with no warranty or guarantee of suitability or fitness for any purpose
whatsoever. Use 'em at your own risk.
All materials on this page copyright
© 2010 by Adam J. Wilt.
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or frame this material for educational purposes,
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it) is expressly forbidden.
last updated 2010.01.29