Greyscale Mode

[crOOk]

Great! I was waiting for a greyscale option in the XviD codec, so I tried it out and created two uncompressed videos to test it out. Then I compressed both videos with a fixed quantizer of 1 in color and in greyscale mode. These are the results:

----------video A-------video B

----------HUE-SATURATION-BRIGHTNESS

frame1----240-66-54----0-0-54
frame2----0-66-54------0-0-54
frame3----120-66-54----0-0-54
frame4----0-66-54------0-0-54

frame5----240-66-54----0-0-54
frame6----60-66-54-----0-0-54
frame7----120-66-54----0-0-54
frame8----0-66-54------0-0-54...

length----------100 frames

resolution-------640*352

size------------67.590.656 B

Three of the output videos contain the same solid grey colour and the fourth one contains the 4 changing solid colours. ALL the videos have the same size: 253952B Did I make a mistake? What does the greyscale option actually do?

[Koepi]

*giggle*

first, your biggest mistake is to use quantizer 1.

second, what do you expect from a perfect b/w video... if there are no colour informations, they _can't_ get coded, so you won't gain anything.

Please read my release notes.

You should try fixed quant. 2 at least, _maybe_ you'll experience a difference there.

[crOOk]

Well, maybe it was pretty dumb to compress the grey video in color and in greyscale mode. I actually only needed video a, the colored one...
But I don't think it actually matters which quantizer I use in this case, the video will be perfectly compressed anyway since there is only very little information in it. But I compressed the video again, using quantizer of 2, then 31. In both greyscale mode and in normal mode the video has exactly the same size. So the color information is not really dropped, is it?
I've already read the release notes before I posted this thread, but I still wanted to find out if I can chieve better compression rates with the new mode. Let's say I had a couple of old black and white war movie dvds, 4 hours a piece. I was interested in compressing them to one cd which shouldn't be a problem withour any color information. If the only advantage would be that the colored noise/dirt whatever disappears I could just use a filter...
What I'm actually trying to find out is: Doesn't XviD just drop all color information first like a filter would, but compresses the video as if it would be colored one? I can also merge a greyscale mode and a normal mode xvid stream into one. I did not expect this to be possible and thought they would be a different format.

[Koepi]

Erm, well, look at this:

EDIT: maybe the link now works...
http://www.xvid.org/modules.php?op=modload&name=phpBB2&file=viewtopic&t=671

You're doing something wrong.

And don't doubt my words here mate, throwing away chroma information where there is none will get you nothing.

It's meant for _noisy_ (I wrote that in the release notes, right?) b/w movies which have "color noise". That's the only situation where you can gain up to 5-10% (and that is a very optimistic guess) bitrate. (I wrote that on the xvid-01082002-1-thread already as well, didn't i?).

[crOOk]

I admit that I just expected too much of the black and white mode. In the thread you linked to it is said that the gain for colored sources in bitrate could only be 10-15 %. That's true, although in the sample i used it's 0%(I guess because it is "perfect" and has so little information...?). I tried it with a colored avi source again and had a decrease of size by 3.2%!! AT least I can be sure that there is some chroma information dropped...

But let me correct you: I did not try to "throw away chroma information where there is none" and i know it won't get me nothing. Well, at first I did, but I corrected this mistake in the second post, didn't I? All I did is throwing away chroma information where there is a lot of it (in the colored video) and I still didn't get nothing (not a single byte) out of it. This did not clear up yet, although it was my question... maybe someone else with better knowledge of the topic can help me with it: WHY CAN'T I SHRINK THE SIZE OF THIS TINY (0.09bit/pixel) CLIP bY DROPPING THE CHROMA INFORMATION???
Another thing I still wonder about is that I only lose 3.2% in size when discarding the color information of the avi video ("Ali", vite release, frame 10000-15000). But I guess that's just how things are.

[Koepi]

Well, at quant. 1 you won't get any differences.

You must at least use quant. 2.

And don't shout, this will only get you branded... (why this demanding sound? If you demand something, you will for sure not get what you want.)

[crOOk]

As you told me before I used a quantizer of 2 and later, as I still didn't see any difference in size, I used a quantizer of 31. Still no difference (I remember writing this before)...

[Koepi]

Well, and now that you are "SO NICE" you think I owe you?

No way.

The chroma information get's dropped. But you see the effect of efficient advanced compression technology. The chroma information doesn't need much space. It's the motion vectors and the textures. It doesn't change the bitstream/file format.

And now stop it. I'm really getting annoyed.

[crOOk]

Well, in this case, the chroma information does NOT need "not much space". It doesn't need any space AT ALL... that's what makes me wonder because even the advanced compression technology of today shouldn't be able to do that.
So there are two possibilities:
1. This one I don't understand.
2. Greyscale mode is not perfect yet.
Well, you should know what to do, you invented the greyscale mode, didn't you? So you should actually be the demanding one here. In case you are still trying to improve it. See what I'm trying to do is help you developers develop an even further advanced compression technology. You just make helping you a tough job by not stopping *giggle*ing about me, by even telling me not to doubt your written word (There's nothing that I cannot doubt) and finally telling me to stop posting to this thread. Well, why don't you just stop posting next time you think a conversation is over. Does this have anything to do with something called the last word... Oh, I forgot: Excuse me, mate

[Koepi]

Well, _I_ won't strike you, but you keep breaking the forum rules.

You really should watch out what you're doing.

_I_ don't welcome you anymore. Maybe you should learn that if you want something you shouldn't insult people, but ask nicely. But I'm not your parents.

My last posts were nice, you kept insulting me by doubting my words, bitching around and writing %&$/&$ (censored).
What's even more insulting is that you doubt that "the color gets dropped correctly". Gruel wrote that code (I just made it accessable for win users), and as you can see in the screenshot above it does a _perfect_ job.

Read the forum rules. Abide to them _or_ never post again where I'm around please.

[spyder]

Hrm, the nerve of people these days. If you really want to help Koepi CrOOk, stop bugging him and let him do something productive. Also, Koepi that's very nice of you not to strike him. I can't say I would have done the same.

[BlackSun]

CrOOk, you have been striked about forum rules #12