Bill in Co wrote:
Well, this is a bit off topic, but I thought I'd just ask.

If one chooses to "grayscale" a video (remove the color info), can one then
recompress the video a lot more while keeping the same video resolution
detail (i.e., due to eliminating wasting storage of any color information in
the compressed file)?

I guess one could ask the same question regarding storing images, too.
IOW, could one convert a 1 MB color JPEG to perhaps 250 KB, and yet retain
the same detailing (minus the color)


I tried it.

1) Windows Movie Maker
2) Drop my favorite test clip (~30 minutes) into timeline.
3) Save output as MovieRGB in "High Quality Video (Large)" format.
4) Go back to timeline. Click on the clip. Select special
effects and apply Grayscale.
5) Save output as MovieGray in "High Quality Video (Large)" format.

Results.

Moviergb.wmv 56,671,234 bytes
Moviegray.wmv 50,380,744 bytes

So not a huge saving. A small savings possible.

Codec info - Video was Windows Media Video 9,
Audio was Windows Media Audio 9.1 44KHz stereo

*******

The lossy compression methods, work in the frequency domain.
Reducing the color palette, doesn't necessarily change the frequency
(sharpness) of the thing. Which is why perhaps there isn't that much savings.

I'll leave the testing of the JPG compression, to you :-)
You can see DCT mentioned in here, as part of the compression.
I like this article, for the set of images versus quality
setting, which is convenient if you ever need to know in
advance, what kind of Q setting to use for a particular job.
Q=10 and 46:1 compression, still looks pretty good. Q=1, not
so much. You could test at a constant Q, try your gray and color
images, and see what a diff it makes.

http://en.wikipedia.org/wiki/Jpeg

Paul