compressibility check

[hassegubben]

If I have done a compressibility check, which has the highest rank-setting the 45-55% value or staying close to the 0,20 bits/pixel value? I often get 65% and 0.20. From what I understand in the Doom9 guide, the best is to increse the resolution if you get >55%? But if I go from 65% to 50 % the 0.20 value drops to 0.17. My first concern is to use as high resolution as possible in order to see more details. So, should I set the comp value to 50% or should I rather stay close to 0.20, in order to get the highest resolution?

[UHT]

once you have done a comp. check you can ignore then .20 etc and just look at the %

[hassegubben]

Thanks. Just as I expected! :)

[pdontthink]

i fail to understand why that figure can be ignored.
surely the bits per pixel figure is important all
the time, since the fewer bits you have to render
each pixel, the lower the quality of the image, no?
why would you just throw that number away just cuz
you have a more accurate idea of the movie's
compressability? if I go back and reencode a movie
with much bigger rez (%) but the bits/pixel goes into
the yellow, will it not look much worse???

[Beave]

It sounds like you do understand it, but well:

A noisy/colorful picture needs more bits per pixel to be encoded than a dark/clear picture. For some movies you even need .35 and above to look good and others are fin with .14.

.20 is a guidance point when you don't know how it compresses. Nothing more.

[UHT]

well said beave

[pdontthink]

my mistake... i wasn't thinking clearly :rolleyes:
and i got it backwards; i tried to say that the
compressability load percentage (is that figure
as simple as I'm thinking... 100% - %compression??)
goes UP when you increase rez, but it does in
fact go DOWN, as you'd expect.

while I'm at it, anyone wanna comment on the
reasons people are saying it's a good idea to
do a new compression check every time you change
the rez???

[theReal]

As far as I understand it the first pass (or comp. check) will check how big the final avi will be when there are no restraints on the codec, using full bitrate (6000). This size is then considered to be 100%.

Choosing a lower resolution will result in that file being smaller (the codec uses full available quality, but there are less pixels to encode -> smaller file)

At the same time, your desired filesize stays the same and will then be a higher percentage of this newly defined 100%

[pdontthink]

that makes sense to me (after thinking it thru
ten times ;>), and if this is indeed the case,
then all those people who say you should run
compression checks every time you change the
rez are dead wrong. any of those people care to
pipe in??

[theReal]

No!
The percentage changes when you change the resolution

Ex.:
At 640x480 you get 43% - this is too low, so you change the res to 512x384, run the comp. checkagain and get 58%

Without running the comp check again, you wouldn't know if 512x384 gave you 50%, 60% or whatever. All you could know would be "it will be somewhat higher than 43%"
For exact numbers you need another comp. check.

[diji1]

theReal is right

[pdontthink]

i stand corrected. duh. when theReal said
the comp check is run with no restrictions,
i thought "ah, rez is one such restriction",
and while it might be a *restriction* of sorts,
it's obvious that you can't run a dumb encode
(or a check) without *SOME* resolution number!
duh. so i get it, i get it. thanx folx!

pdontthink
:stupid:


btw, what are people doing in lieu of a compression
check if they are not using GKnot and just plain
vDub all the way? Guessing, i suppose???

(sometimes my compression checks fail outright; not
sure why... suppose I should read the log, but I
just go with a play-it-safe rez in vDub which usually
works just fine)

[diji1]

... well, there's a number of bitrate calculators around but other than that i don't know any other method of coming up with resolution other than the gknot/avsynth method - kinda why i really like gknot and those compression checks - theWEF be my hero for doing all the hard work for us lazy ppl! :)

[jonny]

Compression check is the BEST!!!
Have someone some technical info on how it works?