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Old 10th January 2002, 23:04   #1  |  Link
kermit23
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16 bit vs. 24 bit

When I use GKnot 0.23beta to make a divx-movie, I get avi's with a 16-bit color depth. This looks very unusual to me, all my other divx movies have a 24-bit color depth. GKnot uses DivX 4.12 and Virtual Dub.
But there's another thing, when I close GKnot, load the avs-file in Virtual Dub and encode the movie with DivX 4.12, then I get a 24-bit color depth avi. This looks very strange to me, any suggestions?
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Old 11th January 2002, 01:01   #2  |  Link
TheWEF
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gknot sets vdub/nandub in "fast recompress" mode.
the video is not converted to rgb but stays in it's original yuv format.
for some reason explorer-file-properties show 16bit for yuv videos.

don't worry, quality is the same.

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Old 11th January 2002, 01:05   #3  |  Link
kermit23
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If, as you say, quality is the same, does that mean that most DivX movies have a maximum color depth of 16 bits although its properties (right mouse click on avi, and then summary) says it has 24 bits color depth, because they've been converted to rgb first?
Or 16 bits is shown, but it is 24 bits?
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Old 11th January 2002, 01:53   #4  |  Link
TheWEF
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http://www.inforamp.net/~poynton/not.../ColorFAQ.html
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Old 12th January 2002, 13:50   #5  |  Link
Acaila
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Quote:
If, as you say, quality is the same, does that mean that most DivX movies have a maximum color depth of 16 bits although its properties (right mouse click on avi, and then summary) says it has 24 bits color depth, because they've been converted to rgb first?
Or 16 bits is shown, but it is 24 bits?
Actual color depth is 24 bits, it's only shown as 16 bits.

Btw, VirtualDub uses the same information as explorer shows, so that a movie encoded in fast-recompress mode can't be joined to a movie encoded in full-processing mode. Unless you change the color depth with a hex editor.

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Old 15th January 2002, 20:00   #6  |  Link
LotharZ
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As I can change the color depth with a hex editor???
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Old 15th January 2002, 20:58   #7  |  Link
Acaila
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It's just a one-byte flag, byte number 187 in the avi.
This doesn't change the actual color depth of each frame, just the flag that is read by programs.

Actually I don't use a hex editor, but an editor that translates hex language into decimal language. It's much easier to search for a specific number, coz you don't have to translate it first before you search.

!Don't change it unless you really need it for something!
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Old 16th January 2002, 09:58   #8  |  Link
rui
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But when using divx3, Gnot displays 24 bits??

By The WEF:

"gknot sets vdub/nandub in "fast recompress" mode.
the video is not converted to rgb but stays in it's original yuv format.
for some reason explorer-file-properties show 16bit for yuv videos"

But, when i make a conversion using Gnot and divx3, the avi file allways has 24 bits. I am not asking because of the 16 bits/24 bits issue. I am asking if this means that Nandub isn't in fast recompress mode.
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Old 16th January 2002, 13:36   #9  |  Link
kermit23
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> Actual color depth is 24 bits, it's only shown as 16 bits.

But when I change my display settings to 16-bit color (instead of 24 or 32), I see no difference in a 16-bit (yuv) movie. So you might think it has only a 16 bit colordepth, because when I play another movie in 16 bits colordepth (for example a DivX, RGB 24 bits so it's encoded in full processing mode!!!), it looks crap (you can clearly see the difference between 16 and 24 bits).
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Old 17th January 2002, 01:17   #10  |  Link
TheWEF
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if you see a difference changing desktop color deph it only means that your hardware-overlay is not kicking in. -> gfx driver problem.

kermit, you can trust me: "16bit" does not mean less quality - period.

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Old 9th March 2002, 17:36   #11  |  Link
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If I set VirtualDub to encode at 16-bit instead of 24-bit, will I get much better compression since it needs to encode so many less colors? I figured it would be better for anime but I don't know. How many colors can the human eye tell apart? Maybe you notice the differences more if it's in a gradient or something..
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Old 19th March 2003, 16:29   #12  |  Link
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To my knowledge all MPEG4 codecs use YV12 color format internally, which makes the true value 12 bit, regardless what windoze chooses to report. (That's why it shouldn't matter at all if you process at '16 bpp' or '24 bpp' for compressibility)
16 bit RGB can be easily noticed on gradients, but 12bit YV12 or 16bit YUY2 are completely diffrent things, since these values are the middle bits/pixel over the entire video, if you look at a single pixel its 24 bit(*), only two(YUY2) or four(YV12) adjacent pixels share the same values in the chroma planes.

(*) This is not completely true since valid streams may not have the full value range per channel (e.g. iirc 16-235 for luma).
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