anyone know what causes the green phenomenon

[maca]

Sometimes when re-encoding a video that's black and white, I'll get that weird effect where there's patches of green tint throughout the picture. An example: I own The Three Stooges collection on dvd, and I shrank them to smaller .avi files for use on a portable player. They look good except for the green that comes and goes. I even converted them to greyscale, but it doesn't go away. Does anyone know this green phenomenon I'm talking about, and how to eliminate it? Thanks.

[jagabo]

Sometimes when re-encoding a video that's black and white, I'll get that weird effect where there's patches of green tint throughout the picture. An example: I own The Three Stooges collection on dvd, and I shrank them to smaller .avi files for use on a portable player. They look good except for the green that comes and goes. I even converted them to greyscale, but it doesn't go away. Does anyone know this green phenomenon I'm talking about, and how to eliminate it?

No. What encoder are you using? Maybe you just have a playback problem. Maybe you could provide a small sample?

[maca]

This has occasionally happened to me throughout the years with various encoders, various computers, and various players both software and hardware. So it's no specific program, just a thing I've noticed with certain files. I've also noticed it on a few movies that have been converted from PAL to NTSC. Years ago, I bought a copy of the old B&W sci-fi movie "Monster from Green Hell" (ironically titled) which was rumored to have been converted from PAL, and it had the green look. It's not like the whole screen is just tinted green, more like the blacks in the image have a greenish quality. I've even seen B&W movies on TV look that way, and there's not a problem with my TV because other movies on the same channel might be fine. I'm sure someone out there must have seen this phenomenon.

[maca]

I'll try to up a pic.

[maca]

These are two episodes from the SAME "Untouchables" disc which I recently purchased. When played on my LCD tv, computer, whatever, one of the episodes has the green throughout. The second example does not. This is the same look that happens with some B&W .avi files I've created, even if I create them as greyscale. I did turn up the chroma a tiny bit on the first pic to accent the effect, as it's very evident on TV but not as much in a screen capture; it seems to vary with movement.

[edDV]

A pic would help. If you are talking about a color shift in blacks or whites, that is often the result of an improper YCbCr to RGB conversion, or visa versa. For monochrome, Cb and Cr should settle to nominal leaving only Y.

In the old analog NTSC days TV stations could force monochrome by killing the color burst on the back porch. TV sets responded by switching off color decoding. The digital equivalent is applying an HSL or HSV filter and forcing chroma saturation S to zero.

[jagabo]

It's not unusual for black and white movies on DVD to be discolored. You should upload a small sample of a video that started out true grayscale and came out discolored after you encoded.

[maca]

It has happened with true greyscale sources, as in my Three Stooges discs. They are pure B&W, but my smaller avi files have the green curse, even though I turned the chroma off in filtering.

[jagabo]

If you're using Xvid select enable the "grayscale encoding" option in the "zone options" dialog.

[maca]

I've been busy and unable to get back to the forum for a while. Grayscale encoding does not help my problem. On two different standalone players, and three different flat panel LCD TVs, the image turns green now and then. I just did a Three Stooges, for example, which looks great for the most part, but any scene which features a lot of white will turn the shadows green. This doesn't occur in my original dvd, just in the xvid encode.

[poisondeathray]

Weird...I've never seen that on pc media players, DVD standalone units, or media boxes

Did you decrypt the discs before encoding to xvid ? What did you use ?

Can you explain the steps you used to convert to xvid ?

can cut a small sample from the episode that has it throughout and upload it to the site ?

[jagabo]

With Xvid's grayscale option enabled the chroma channels are ignored. So any problem is in playback device(s) or a bug in the particular build of Xvid you are using. You could verify this with an AviSynth script:

AviSource("filename.avi")
u=UtoY()
v=VtoY()
StackHorizontal(u,v)

Open that with VirtualDub or any editor or media player and you should see a flat (no detail) medium gray image.

[manono]

Are you using any Xvid custom matrices, anything other than the default H.263 or MPEG? I had a DVD/MPEG4 player once that sometimes turned the Xvid video greenish when I used a certain matrix.

[AlanHK]

Sometimes when re-encoding a video that's black and white.

Using what software?

I've done some heavy filtering of old b/w movies and sometimes that causes a bright green tint on b/w.
I use Avisynth, so I just put a "Greyscale()" at the end of the filter chain.

[Bjs]

Encoding type ?

VBR vs CBR

So what is used during encoding ?

[maca]

@manono

I'll have to check the matrices. This happens using AGK, or TMPGEnc Express with xvid selected, or indeed any converter with xvid selected. Haven't tried divx to see if it's immune. Maybe something corrupt in my xvid as others have suggested. I'll get another install and try again. But this isn't something that's just started; it's been going on for years with different computers, different players, different TVs. I just thought it was a standard issue that someone would have a fix for. Oddly enough, it doesn't show up as much on a computer monitor, but on every LCD TV and standalone player that I have. So it's almost like it's something that doesn't rear its ugly head until NTSC is in the mix. HDMI, component video, composite video, it doesn't matter; they all do it.