Why are black & white material so hard to compress? 30% plus bigger than color stuff?

[Ponder]

Sometime it seems 60%-90% larger even the materials are smooth as silk. Using
greyscale() does not help. Greyscale material has much less info, shouldn't it be compressed
to much smaller size than color source? :confused:

[pbristow]

If the source is very noisy, or has much more genuine detail, then it will be harder to compress than a clean and/or soft source. Is your black and white material from old movies, perhaps, with lots of scratches, dirt and film grain?

If you post an example of something you're having trouble compressing (just a few seconds worth should suffice), people might be able to advise you better.

[Ponder]

@pbristow

On "Dead Man",a low motion drama dvd, no grain, 100% smooth, using crf 21.2,
got 1470MB with 1617 Kbps. :confused:

[Mug Funky]

black and white film is sharper.

1 layer of emulsion means no diffraction effects, meaning sharper pictures vs 3 layer colour negative.

it may also have been sharpened at some point.

Dead Man certainly is not grain-free, either. and B&W grains are finer.

all other things being equal, B&W should be a little bit smaller than colour, but all things often aren't equal.

[Ponder]

@Mug Funky

Very nice explanation, since it is visually hard to spot such fine grain, with no many degrainers
around, dont want to use a big knife (overdone) to slice such fine grains. Which degrainer(s) are
very good at, also reasonable fast at such "black & white" dvd. I generally use undot, and lately
RemoveGrain(1) did not help here, obviously. How big are fine grains for dvd, 2,3,4 pixels wide?

[Dark Shikari]

Color information is typically less than 10% of total bitrate. The cost of the grain in black and white films is significantly greater than the amount saved by lack of color information.

[sumawo13]

@pbristow

On "Dead Man",a low motion drama dvd, no grain, 100% smooth, using crf 21.2,
got 1470MB with 1617 Kbps. :confused:

Try using a higher CRF? :)

[manono]

It's a completely pointless question. Encode a color movie and then greyscale that same movie and encode it again with all other settings the same. Then come back and tell us the size of the black and white version is 60-90% larger than the color version.

[Ponder]

@Dark Shikari
Wow, good to know the scale is not 1:1 between planes.

[Ponder]

@sumawo13
Saw the source very smooth, common sense is to assign a lower crf since same crf on smooth color
are 900 to 1200 Kbps. Was really surprise, it turned out this big. With the good explanation from
Mug Funky and Dark Shikari, now all clear. Did not find any good info regarding BW compression,
now everyone who does not know it benefits. Next time will use crf 42, or maybe 24.

@manono
You are way over analyze the simple question of smooth color vs (smooth) BW source on size.
There was no recompression mentioned or used. Saw "smooth" BW source, greyscale and undot it,
since it looked smooth as silk, used low crf 21.1. Sensing a bit of caffeine here ;-).

"Dead Man" was just an example answering pbristow's question.

[ramicio]

Greyscaling a color film is not the same as shooting with B&W film in the first place.

[Ghitulescu]

Each BW film has its own characteristics (which are taken into consideration by the skilled director and his technical stuff). This includes the distribution copies, too.
Also a greyscaled (decolorised) movie is not simply a Y-only movie (it shouldn't be). There are algorithms to greyscale a movie, for instance to match eg a particular film type (eg KODACHROME Type 5267).
As long as the graying the colour film to match a real life BW one, there will be no difference in terms of colours. It will be maybe in terms of resolution, or noise, or grain, all of these depending on the scanning-digitisation.

[manono]

Greyscaling a color film is not the same as shooting with B&W film in the first place.

Of course it isn't. That's one reason it's a pointless question. It's an apples to oranges comparison. Different sources compress differently. You can't take one that's 60-90% larger (in his own words) than a completely different movie and then conclude the reason for the differing sizes is because one's in black and white and the other's color.

[Ponder]

@ramicio
I know some movies are tinted (artistic), fake BW?, The "Dead Man" I saw is BW visually.
http://www.imdb.com/title/tt0112817/. and I are both fooled?. So modern BW are likely fake BW then,
if greyscale it, size shootups a lot, if not greyscale it, size normalizes to 900-1200Kbps.

Is this what you mean?. If so, won't use greyscale in general.

@Ghitulescu and @manono
Good to know some more technical info here. Mug Funky and Dark Shikari basicly clarified all
these aspects I did not know. ie. There are more sharpness of BW than color sources, very
fine grains in BW than in color source, and "color information is typically less than 10% of total
bitrate" which I did not expect either.

So what I saw smooth as silk, low motion (thus low bitrate encoding outcome, hence used low crf)
BW source, apparently, the encoder saw it much sharper and grainier. Now I know why my color
encoding are very consistant in size and very much smaller than BW source using similar crf.

Read somewhere greyscale speed up encoding, so I used it on BW sources and hoping it helped to
reduce size as well intuitionally.

How do I know if a modern BW source is fake greyscale, other than visually?
Now I incline to believe most if not all labeled modern BW sources are fake BW.

[ramicio]

The only way for you to know is if the person making the movie talks about how they made it, like people like James Cameron talk about how they make their movies. I don't believe your size is strictly because of it being B&W, it's because you use CRF, which is not a good method if you want sizes to be even mildly constrained.

[Ghitulescu]

"Visually BW" is not visual. It's real BW. Or at least it should be. The director chooses BW because BW has something "to say", like the "cinema noire" of the '40ies. The director decides, according to the script, whether s/he would go BW or color. Because this is correlated to costs (filming, reproduction, stocks etc.). BW is shot differently than colour and the cameraman should be confident s/he will manage to handle it.

[Ponder]

@ramicio and @Ghitulescu
I was not concern about exact size, 700MB thing. 900MB is fine with me. But 1400ishMB on a
visually smooth, low motion drama (tons of sit and talk scenes) puzzle me a little and wasteful.
It is not the crf at fault here, perhap a little. Similar crf on color stuff, gave both good quality
and small size. it is much more likely due to the sharpness(very low gradient on all edges) and
very subtle grain added during production as mentioned by Mug Funky.

Solution is plain simple now, On BW sources (fake or not) dump greyscale, use crf23-4ish. Try encoding
10 second clip to see size, since visual inspection not a bit reliable, if high bitrate, try
some older degrainers which are probably better at SD.

[Ponder]

With crf 23.7, SPresso(6,29,17), and fluxsmoothT(7),

Size dropped from 1470MB to 565MB, still very good quality. crf 23.7 alone cut off 60% on short
clip test. So it is verified now very fine BW grains (hard to spot) and low crf 21.2 blowup
bitrate. fluxsmoothT(7) was not needed at all, no dancing anything, still cut size by 20%,
but I was curious to see its effect. Crf 23.4 and SPresso(4,29,18) is probably good enough here.