[Bf-committers] Color correction in sequencer.

Roger Wickes rogerwickes at yahoo.com
Thu Dec 11 04:20:01 CET 2008

>From a user perspective, there are two problems that need a solution. The first is that a shot is just off-color, perhaps is not snappy enough. The second issue may be that different shots are filmed under different lighting conditions, and in order for shot 2 to look contiguous to shot 3, the color balance and luminance have to match pretty closely in the rendered output.  A related issue is that you want all shots related to a topic or set to have a certain color spectrum, regardless of their actual filmed color. Therefore, you want to adjust the actual footage (strip) to have some color historgram.

We already have display modes that give us color spectrum info, and act like gauges. What we need is a tool to help us adjust our input so that we get the "right" values, at least according to the gauges give us the right values. 

For the first issue, just a good understanding of what to fiddle with to make certain kinds of corrections is needed. Anything that is in somewhat common with other areas of Blender (shaders, nodes) would be easier to remember. For the second issue, some fairly straightforward way to use the other VSE display modes (historgram, vectorscope, luma) and a tool to make them match some other (rendered or reference image) is needed; some way/lift/gain/adjustment tool color correct/adjust different shots (strips), each differently, so that together they flow. in other words, strip A + adjustment A == strip B + adjustment B. 

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From: Xavier Thomas <xavier.thomas.1980 at gmail.com>
To: bf-blender developers <bf-committers at blender.org>
Sent: Wednesday, December 10, 2008 6:28:02 PM
Subject: Re: [Bf-committers] Color correction in sequencer.

they are not really intuitives, but they works like "Levels" in gimp
Lift must set the black level
Gain the white
and Gamme the mid point

The problem here is that the the values are manipulated for :
- "1,1,1" to be "no change value" 
- Values between 0 and 1 to darken the image
- An "inverse" button tho permit values > 1 wich brighten the image
More than being unintuitives, it does not permit full control (inversing gain invers for all channels)

What solution:
- Curves will take big UI
- Levels maybe also

But it is not preferable to do this as an sequencer effect, This will permit the user to choose the effect acording to the type of correction he wants to make (Level, curves, ...)

For primary color correction this is not really important as for me "Levels" and "Lift/Gamma/Gain" are the same with different way of setting the parameter and they can be done with curves. 

But if complex secondary collor correction (like changing saturation  and value acording to hue with a curve, ...) is going to make is way in blender the user must choose the one he wants

Note that with nodes doing a "not so complex secondary color correction" (like the exemple below) requires:
-color space conversion
-doing a difference map with a constant value
-using this map as factor for color

It will need about 10 nodes and that is uaualy done in one in shake or with one effect in finalcut.

I am interested in this kind of stuff and I can code it but as I said if is going to be used by nodes, sequencer and image editor ther must be a way to unify it.


2008/12/10 Campbell Barton <ideasman42 at gmail.com>

On Thu, Dec 11, 2008 at 9:33 AM, Xavier Thomas
<xavier.thomas.1980 at gmail.com> wrote:
> Yes, that is what I ment but is it ok to add an UI parameter "ofset" with is
> button "Inv ofset" at the side of the Lift gamma and gain parameters because
> the UI will get really charged.
> And what about an image treatment library, because I already have made this
> function in my keyer node and crating a color correction node with these
> controls might be usefull also: this will result in a lot of code
> duplication.
> 2008/12/10 Dalai Felinto <dfelinto at gmail.com>
>> Hi Xavier.
>> Can't you do a do_version()?
>> In readfile.c you can see a lot of parameters that need to be updated
>> over Blender version.
>> If what you need is a simple offset for old blender files work in the
>> same way as new blender files (with this bug fixed), this should work.
>> I didn't see the bug or this part of the code, but do_version()
>> sometimes is the better way to go.
>> Cheers,
>> Dalai
>> http://blenderecia.orgfree.com
>> 2008/12/10 Xavier Thomas <xavier.thomas.1980 at gmail.com>:
>> > Hello,
>> >
>> > Lately, I was trying to implicate me in blender developement,  and
>> > begining
>> > with small things (after the keyr node) I  desided to correct this bug:
>> >
>> > http://projects.blender.org/tracker/index.php?func=detail&aid=18010&group_id=9&atid=125
>> >
>> > Basicly the lift parameter of color correction in sequencer works more
>> > like
>> > a "value" color correction than a "lift" (exept that it work on RGB
>> > channel
>> > separately so I think "ofset" is more apropriate then "value")
>> >
>> > Fixing it would be simple but old files that use this parameter will
>> > have a
>> > diferent render result, and after discussing with Matt Ebb on IRC it
>> > seems
>> > that this is not acceptable.
>> > So the only solution to have a proper color correction in the sequencer
>> > is
>> > to add an "ofset" parameter. Is this OK ? (maybe the UI will get too
>> > compact)
>> >
>> > Further, why do not put this kind of function in an image library so it
>> > will
>> > be accesible form other part of the program (nodes and maybe image
>> > editor)
>> > like the quick blur function in the nodes CMP_util.h
>> >
>> > Sorry to disturb, I know lot of you are really buzzy but I prefer to get
>> > good directions before coding.
>> >
>> > Thanks
>> >
>> > Xavier
>> >
>> > _______________________________________________
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Recently I tried making sense of the sequencer's color functions and
found them quite confusing. Even after tweaking them for 5min I don't
really understand what they do exactly.

Id much prefer convert these values into either, gimp/photoshop color
'Levels' or 'Curves'.
Curves are already used in other parts of blender so I'ts probably not
that hard to make this change,

Peter, if your reading, Could these settings be converted to curves?
(even a close approximation would be ok I think)

- Campbell

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