Fixing colors - removing some yellow/white

[DarkT]

Hi,

I have some home-videos which were shot with different "modes" in my camera, and soem under bad lighting.

For example one set of videos came out too yellow, because there was too much "yellow-lamps" lights around...

Another seems too "white" or something, like under floroscent...

Yet another has some green tint to it because it was shot in a room with lots of green stuff - which I GUESS somehow bounced, or maybe the camera tried to auto-calibrate or something...

Basically, how would I try to minimize one color in avisynth? In photoshop tehre are filters with which you can play to get this done... to some degree...

Thanks.

[wonkey_monkey]

Have you tried:

coloryuv(autowhite=true)

To quote the documentation, "it isn't very intelligent", but you can use the other parameters to do a manual correction of colours.

David

[7ekno]

The issue is "is the issue dynamic or static?"

Meaning, does any part of the too yellow video actually appear "normal" or not?

If it's constantly a set yellow all the way through, you can use "coloryuv" with the "offsets" to adjust the entire clip, but if there are area of the clip that are "normal" they will now be "too green" ...

If the "too yellow" or "too white" is dynamic, the only way to do it is to use the above "autowhite=true" then manually adjust the offsets to your personal preference (after autowhite I like to add 3 yellow and 3 red just to make skintones a little more soft) ...

7ek

[StainlessS]

Hi DarkT,

Try using TMPGenc (the old Mpeg1 free version will do) Custom color correction.
click Add, the default will add RGB, change this to YUV and play with the U and V sliders
until you get somewhere close, this should give you a little bit of an idea where you should
be heading. By 'too white', I take it that you mean too blue, it appears ultra white
like under floroscent, as you say. Also, TMPGenc has a good little function called
'OverLay', all this does is make the background Magenta,. When staring and trying
to correct colors, your eyes tend to start going funny, and you can actually
over compensate and make it just as bad but in the opposite direction. Flicking on
the 'OverLay' for a time and then off again, forces your brain to start seeing colors
more accurately again. When you feel you are in the right ballpark, then use
ColorYUV(off_u=0,off_v=0), replacing the zeros with whatever you decide.
Also, using cont_u and cont_v will alter color saturation, you would almost
always use identical value for each, +ve will increase saturation. If you can find a
frame in your vid with a great deal of what should be true white, then you may
see a spike in both chroma channels of Histogram(mode="levels"), there is a very
good chance that if you can centre those spikes, the job will be done.

:)

[StainlessS]

Hi Again DarkT (If your still there)

See Below:-

http://www.filefactory.com/file/a144e1d/n/ShowChannels_25_dll_20091226.zip

A simple plugin to display average chroma for each frame
and the accumulated average chroma for the clip 'scanned
so far'. Accompanying text from plugin:-


ShowChannels() v0.0

(c) 2009 Stainless Stephen (Jones) [StainlessS @ Doom9]

Plugin for Avisynth 2.5

YUY2 and YV12

Simple plugin whose only function is to display the average
Chroma U and V values for a frame. Also shows accumulated
average for all frames visited so far [In parenthesis ()].


Usage:-

ShowChannels(clip Last,bool ver)

Where:-
Last is the clip

ver display version info, false OFF [default] , true ON



In a well balanced clip containing lots of different scenes and types
of scenes, both chroma U and V values should be about 128. As chroma
values are offset by 128, a greyscale (eg black and white) clip should
result in both U and V values being 128.
If a clip looks too yellow or too blue etc then may be the vid was
snapped using colored lighting, or perhaps there are other reasons why
the color balance is not quite right. This plugin allows you to see the
the overall 'slant' to the chroma offsets and may (or may not) allow you
to better correct color balance.

If for instance total accumulated U is 124, and total accumulated V
is 136, then the U offset is 4 less than 128 and the V offset is 8
more than 128. You might like to try in this case:-

ColorYUV(off_u = +4, off_v = -8)

This should balance the whole clip around central U and V values of 128.

However, not all vids behave exactlty as you would like them too, if say
your film a scene outside in a field containing lots of 'green stuff', then
the scene should in fact be greenish, overall. Correcting a scene like this
as outlined above will not work too well. In a lot of cases, it is perhaps
best to only correct about half way, so instead of the above suggestion, you
might actually like to try a half baked correction ie:-

ColorYUV(off_u = +2, off_v = -4)

You would of course have to judge for yourself whether there is any improvement
or not, ShowChannels() is just a little aid in doing so.

Also shows average Y luma channel, of lesser use.


I dont think I'll bother putting it up on WarpEnterprises,
so if you want it, grab it. Dont know how long it will
be available from above link. :)

[DarkT]

Thanks... I ended up not touching the colors... whateve rI do, the blacks start becoming blue! slightly, vbut I notice, and I'd rather the color be a bit burned into the reds rather than the blues, reds are less... noticeable... more natural...