Movie with "long" black and white scene

[kittychan]

yooooo

First of all I did a search (http://forum.doom9.org/search.php?s=&action=showresults&searchid=807368&sortby=lastpost&sortorder=descending) and I could not find a answer to my question, I decide to make this post. I hope I am right ^_- .

I want to encode (using Xvid 1.02) a video in which there are really long black and white part (more than 60%) so I want to use the "greyscale encoding" option to optimize the result.
My question is which weight in the zone option tab do I have to set for the black and white scenes?? Knowing that color and BW part are equal in action/low-high motion. I think greyscale encoding really reduce the needed bitrate but I cannot evaluate it so leaving a 1/1 weight seems for me to be a big loss of space and/or loss of bitrate for the color part.

Hope someone can help me!

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kittychan

[E-Male]

shouldn't the codec automatically reduce the bitrate for "easier" parts like b&w?

[manono]

Hi-

B&W scenes don't need appreciably fewer bits to encode at the same quality as the color parts. Forget using the zones for this. Just use:

Applyrange(FrameStart,FrameEnd,"Tweak",0.0,0.0,0.0,1.0)

to greyscale the B&W parts. Here's more information on the built-in Tweak filter:

http://www.avisynth.org/Tweak

And on ApplyRange:

http://www.avisynth.org/Animate

[kittychan]

yoooo

thank you for your reply


Originally posted by manono
B&W scenes don't need appreciably fewer bits to encode at the same quality as the color parts. Forget using the zones for this. Just use:


ok so my intuition was wrong....
I really thought that B&W would be easier to encode

Anyway, about Applyrange+Tweak using avs script, does it make exactly the same job that "grey encoding" in Xvid option? Doesn't it?
(maybe avs script give better result in terms of encoding speed...)

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kittychan

[sysKin]

Grayscale Encoding just throws away colour information before they made it into bitstream. It doesn't affect encoding speed (and hell it could at least do that ;) ) and it doesn't really change anything if material was black and white in the first place.

Radek

[loni_blues]

Sorry, but don´t understand.
Shoudn´t greyscale encoding be able to handle the job correctly then? Why forget about zones in the first place?
Thanks for any help.

[lordadmira]

I think the main purpose of the greyscale setting is to blow away chroma flutter in ur source material.

U can use a zone to do this, it'll work just fine. Just also check 'start with keyframe'.

Radek, did anybody ever get to the bottom of that pink coloring problem showing up in B&W areas?


LA

[sysKin]

Originally posted by lordadmira
Radek, did anybody ever get to the bottom of that pink coloring problem showing up in B&W areas? Yes I'm afraid so. They are DCT inaccuracies in intra frames, which later might be amplified by sub-pixel motion filters. If chroma information is always discarded, there is no way for the codec to correct these errors.

[lordadmira]

So the DCT is incapable of dealing with luma only encodes?? That's rather amazing. Any potential solutions in the pipeline? Maybe instead of discarding the chroma information it can write zeroed out chroma planes.

[Teegedeck]

So do I understand correctly that we'd better only use Avisynth's 'greyscale()'?