DivX B&W vs. Color

[setarip]

Anyone know the technical reason that DivX doesn't compress B&W videos as much as it does color videos?

[khp]

What kind of source material are u talking about here ?.

To make a fair comparison between color and b&w encoding, you would have to make a lossless conversion of a color clip to b&w and try to convert them to divx useing qualitybased encoding, is this what u have done ?

[setarip]

The source material is, in all instances, commercial DVDs.

[GFGodoy]

DVD's aren't allways the same quality. Some of them are single layered and have some noise in the image (which is really a pain in the ass for divs ) some are interlaced that also uses a lot of bitrate.


Also, the B&W movie may even be old and dirty and those black sparks also makes compression difficult...

[setarip]

To GF Godoy

Although I appreciate your speculation, I'm fairly certain it's not applicable.

I have created .AVIs from MANY commercial color DVDs and MANY commercial B&W DVDs - and have determined that, WITH ALL OTHER THINGS BEING EQUAL, the color DVDs compress approximately 20% smaller than do the B&W DVDs.

Hopefully, someone can provide the technical explanation for this consistent disparity ;>}

[GFGodoy]

Could you tell us what method you are using for conversion??


And second: if you have already converted allot: have you compressed the Woody Allen's "Famous" I think (the one with Leonardo DiCapri Urgh!!!). This is a new movie, which has no noise at all, and doesn't have those "old" thing effect on the Film itself.


I have compressed Lolita, Dr. Strangelove and Sahara, all of them in 2 pass mode. Havent noticed anything like poor pixelation or something.



What are your doing? (method)

[setarip]

"I have compressed Lolita, Dr. Strangelove and Sahara, all of them in 2 pass mode. Havent noticed anything like poor pixelation or something."

I know you mean well, and I thank you for trying, but it's apparent you're not comprehending my question...

[khp]

I know you mean well, and I thank you for trying, but it's apparent you're not comprehending my question...

Well you have not exactly been forthcoming with any details on you problem despite repeated requests. Which I think is kind of insulting, to say the least.

Anyway I have completed trials of Color vs B&W encoding.
And as expected DivX does slightly better on the B&W (6,3 % to be exact)

My test was done as follows.

movie: WildWildWest pal version
(only used 1 vob which contained 25 minutes of video)

Encoding method: followed this guide

http://nickyguides.digital-digest.com/DVD2AVI.htm

no resizeing, no chopping, no audio.
DivX codec: 4.12 using Quality based encoding at 95%.
I'am useing qulitybased encoding because it's the only way that filesize can be used as a meaningful measure of compressability.

Only difference between the color and b&w run was the addition of the greyscale filter in vdub.

Results:
color encoding: 330 MB avi file
b&w encoding: 309 MB avi file

[setarip]

To KHP

"Only difference between the color and b&w run was the addition of the greyscale filter in vdub"

I'm afraid that converting to grayscale (256 colors) is not actually the same as dealing with true B&W (2 colors) - but I appreciate your thought and effort.

By the way, my previous response was directed to GF Godoy, who was referring to, "Havent noticed anything like poor pixelation or something." - which has nothing to do with my question/quandary. Perhaps it would have been clearer if I had captioned my response "To GF Godoy"...

[khp]

Perhaps it would have been clearer if I had captioned my response "To GF Godoy"...

Nothing is unclear, I just feel appalled by the complete lack of solid info you have provided, the fact that u are talking about 2-color movies comes as a complete surprise to me.

It does however explain alot, compressing a 2-color image is inherently much harder than compressing greyscale or color images.
For a detailed explanation why, do some reading on how jpg image compression works.

BTW what commercial DVD's are 2-color ?

And why have you posted this in the general forum when there is a perfectly ontopic group for this ?

[setarip]

To khp

"For a detailed explanation why, do some reading on how jpg image compression works."

Thanks for the suggestion as the thought of correlating still image compression concepts with video never occurred to me.

[GFGodoy]

Ok, so, let me see if I understand your question:

You are compressing a 2 color movie which is BLACK/WHITE only movie.

I don't know of any source of video that has some little amount of colors.


So, a 2 color movie does not have any grey/lightblack/darkwhite. (????) Sure about this??



I don't mean to be sneaky, but what movie are you compressing???

(Now I am as curious as you LOL )


And 2nd: did you make a qualiy based compression as suggested before? Show us you're results in a 10 minutes clip or something like it.

[khp]

did you make a qualiy based compression as suggested before?

When we are talking about 2-color material, my previous suggestion about useing quality based encoding, for a side by side comparison, is not applical.

[GFGodoy]

yes, I understand.... But how does a 2 colour movie works???

Not even "Trip to the moon" (190X) is doubled colored, you can see shades of grey in it right?


Define the difference of greyscale and 2-colour movie to me.

I don't understand. (perhaps I'm missunderstanding something)