B/N ,colors and size question!

[boombastic]

I've got a question:the same movie encoded with colors or totally in grayscale with the same other settings in Xvid will have the same size?If not in which case will it have the larger size?

[unmei]

Since in xvid (like all mpeg), the color (chroma) and luminance are encoded seperately, when using grayscale there is nothing to be encoded in the color plane. This should save bits - on the other hand if the movie actually is b/w there would not be much in the color plane even if you encode "in color" and the difference to using grayscale is probably not big, maybe even none at all (if the source has absolutely no variance in color values).

Someone correct me if this assuption is false, but i think YV12, the colorspace used in mpeg-4 has horizontally double the luma resolution than chroma, and in horizontal direction the same resolution both for color and luma. Therefore, a full color movie with assumed the same "complexity" in luma and chroma would distribute bits on chroma:luma = 1:2. Removing the color would thus save you one third, making the grayscale 67% the size of the colored version. I hope i did not confuse you too much ..

[RadicalEd]

You're thinking of yuy2. yv12 stores chroma in half horizontal and half vertical resolution.

[unmei]

ah well, same reasoning but 50% instead of 67% :p - thanks RadicalEd

[Leak]

Originally posted by unmei
ah well, same reasoning but 50% instead of 67% :p - thanks RadicalEd

I take your 50% and raise them to a whopping 80%... ;)

(Luma takes up 4 times the space of chroma, so by dropping chroma you'll get down to 4/5ths of the space both takes...)

np: Lamb - All In Your Hands (Fear Of Fours)

[RadicalEd]

But there are two chroma planes, so the luma is really 2x the chroma :|

[Leak]

Originally posted by RadicalEd
But there are two chroma planes, so the luma is really 2x the chroma :|

Oh, umm, errr... you're right. *weeps*

Which, of course, brings us back to 2/3rd (or 66.6666...%) of the filesize when including chroma.

np: Richard Devine - Resource Leak (Lipswitch)

[RadicalEd]

Originally posted by Leak
Which, of course, brings us back to 2/3rd (or 66.6666...%) of the filesize when including chroma.

The irony.

[Koepi]

... so you figured that chroma doesn't take up as much space as luminance by the colour space definition.

To make things worse, chroma gets compressed much higher than the luminance information as we're using the effect that the human eye is quite weak when it comes to proper colour recognition.

So encoding greyscale instead of colour (only if there is colour information of course) will give you around 5-10% more compression.

I hope this helps,

regards
Koepi