bitrate needed in B&W movies

[Susana]

Well, that's my doubt. I think B&W movies need half bitrate than color movies for same compression quality or level. Is this true ?

Thank you very much.

[manono]

Hi-

I think B&W movies need haft bitrate than color movies for same compression quality or level. Is this true ?

By haft, do you mean half? And are you asking if B+W movies need half the bitrate of color movies? Since B+W movies are often older, grainier, noisier than are color movies, I'd say, if anything, the opposite is true. B+W movies often need a much higher bitrate than do color films, for the same quality, since they often compress so poorly.

[Hard Core Rikki]

Regardless of the quality of the source, but assuming you're using colored DVD footage in this case:

Technically, BW movies should require 1/3 of the bitrate required for their fullcolor version. Aiming for little more is recommended.

Assuming that you have the same (color) source, it'd be safe to assume BW'll require a little more than 1/3 usual bitrate to achieve the same "quality" as its colored counterpart.

Of course, that is, if the video is encoded with a "greyscale" option, just to make sure the colors dont bleed outside of the greyscale range.

[Susana]

Thank you, yes, "half" not haft; thanks manono.

I'd say, if anything, the opposite is true. B+W movies often need a much higher bitrate than do color films, for the same quality, since they often compress so poorly.
yes, I agree but you're not taken into account absence of color information ?

Technically, BW movies should require 1/3 of the bitrate required for their fullcolor version. Aiming for little more is recommended.
But color space in dvd is YV12 or 4:2:0 so technically 1/2 not 1/3

Of course, that is, if the video is encoded with a "greyscale" option, just to make sure the colors dont bleed outside of the greyscale range.
Interesting. Does the encoder not recognize B&W ? If a use for example DVDRebuilder for recompress a B&W DVD with CCE, the Monochrome option has to be enabled in the Picture Quality window?

[Blue_MiSfit]

remember that there is chroma subsampling.

chroma gets 1/4 the information of luma in 4:2:0 (yv12) IIRC.

[Mug Funky]

from subsampling alone, there'll be 2/3 the data.

however, there's no luma-only option for mpeg-2, meaning that the chroma is always coded, even if it's flat grey.

also bear in mind that chroma information is quite blurry - so that in colour footage there's not much detail in the chroma channels (usually just flat areas, reasonably sharp edges between objects, and some grain, often quite a lot). a lot of the info that's in chroma signals compresses a lot better than the luma counterparts.

often it's a good idea to apply a heavy-ish denoiser to chroma (so long as it preserves edges).

you'll get a speed bonus in CCE with greyscale encoding though.

[Trixter]

however, there's no luma-only option for mpeg-2, meaning that the chroma is always coded, even if it's flat grey.


Yes, but flat grey that never changes hardly takes up anything.