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How technically Emulate a Temperature/Tint tool

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Gabriele Turchi
How technically Emulate a Temperature/Tint tool
on Oct 25, 2011 at 2:18:10 pm

I was wondering :

technically what tools in resolve should be used to emulate a Temperature (white balance ) and tint Tool ?

a temperature slider (present in may apps (as well as the Red Tab) does it work in Gamma only ? or lift gamma gain together ? or is it a RGB offset ? how about the tint ?

ps:off course i am keep requesting this tool in resolve (very easy and technically accurate for overall quick WB)

thanks

g

Davinci Resolve Control Surface
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Blase Theodore
Re: How technically Emulate a Temperature/Tint tool
on Oct 25, 2011 at 5:30:48 pm

I second this request for an emulated temp+tint control.


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Mike Most
Re: How technically Emulate a Temperature/Tint tool
on Oct 26, 2011 at 5:56:28 am

You can use the Color Mixer, which is essentially a color matrix. A color temperature control basically alters the image along the red/cyan axis, and a tint control along the green/magenta axis. So to change the color temperature, you can change the blue component of the blue channel and the blue component of the red channel. In other words, to "lower" the temperature, lower the blue in the blue channel and raise it in the red channel. To "raise" the temperature, do the opposite. To change the tint, change the amount of green in the green channel.

The color mixer can be an extremely useful tool for things like this. In a show I currently work on, we had a number of scenes that were shot on Alexa but had an incorrect lut applied that shifted the color temperature and made the image very blue. By using the above technique, I was able to "normalize" the scene even though there was no "raw" image available.


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Gabriele Turchi
Re: How technically Emulate a Temperature/Tint tool
on Oct 26, 2011 at 2:14:13 pm

Nice One Mike (as always)
thanks

(i always used the RGB offset to "normalize" the WB...)

ps:what do you mean by "wrong Lut "? couldn't you re-apply lut ?
or maybe was backed-In on a QT export maybe ...

sometimes on alexa when i have the Log C image looks worm and nice , but applying a LogCtoVideo +709 matrix (the WB gets weird (blue/green) ,

i had this experience even yesterday ,the lut i applied was created on the Alexa website (so one of the latest ) , and the Lut that came with resolve game me basically the same results ...

so isn't the WB on the alexa something that the Lut does not (wrongly) influence ?

thanks

g

Davinci Resolve Control Surface
MacPro
Cubix desktop 4
2 Red Rockets
GTX470+GTX470+GTX285
24GB RAM
HP Dreamcolor
Panasonic 58PF Plasma


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Mike Most
Re: How technically Emulate a Temperature/Tint tool
on Oct 27, 2011 at 4:00:34 pm

>ps:what do you mean by "wrong Lut "? couldn't you re-apply lut ?

I could if I was working from the original material. However, that is not the case. The show in question transcodes everything to DNx115 and hands us a mixdown, there is no conform. I don't necessarily think this is a good way to post a show, but numerous shows are doing it anyway, so you have to make do with what you get.

>sometimes on alexa when i have the Log C image looks worm and nice , but applying a LogCtoVideo >+709 matrix (the WB gets weird (blue/green) ,

A LogC image is not meant to be looked at or judged for color. It is a data container. It is not a sensible image until is is "normalized" and has a color matrix applied, which is what the LUT does. I would refer you to my blog (mikemost.com) for more information (or opinion, call it what you will...) on that subject.


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Blase Theodore
Re: How technically Emulate a Temperature/Tint tool
on Oct 26, 2011 at 4:23:00 pm

Thanks Mike! Conceptually I understand the rgb mixer, but practically I use it as more of a black art than a science. Can you elaborate more on how you use it? In a warm image you're lowering blue/blue and raising red/blue, but you're not also raising green/blue?

Could you elaborate on the following, so I can more fully wrap my head around this?

- warm image
- cool image
- image with magenta cast
- image with green cast


Thanks!
Blase


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Mike Most
Re: How technically Emulate a Temperature/Tint tool
on Oct 27, 2011 at 4:07:09 pm

I specifically avoided using the words "warm" and "cool" because it seems to confuse people, as your post indicates. I did refer directly to color temperature, which is a number, measured in degrees Kelvin. A higher number is closer to daylight, which is very blue. A lower number is the opposite of that, or orange. So if you want to make a blue image less blue, you'd be lowering the color temperature, and vice versa. This requires a move along the red/blue axis. A tint control usually works along the opposing axis (opposing by 90 degrees), which would be the green/magenta axis. Since magenta is not a primary color, you control the tint by changing the green component of the green channel. The default in a typical matrix is to have the red channel consist of 100% red and no green or blue, the green channel 100% green with no red or blue, and the blue channel 100% blue with no red or green. So to move the information along an axis, you subtract the main component of one and add it to the other. That's why I subtracted blue from blue (the one I wanted to move) and added it to red (where I wanted it to move to).


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Oyvind Stiauren
Re: How technically Emulate a Temperature/Tint tool
on Oct 27, 2011 at 4:55:41 pm

I just would like to add that moving the gain trackball along the correct axis effectively does the same thing as Mike describes above. It's just easier to make sure you stay on the correct axis with the color-mixer method. Moving the gain trackball is moving the white point.

--
Oyvind Stiauren
Post production supervisor, Colorist
Terminal

Mexico City


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Gabriele Turchi
Re: How technically Emulate a Temperature/Tint tool
on Oct 27, 2011 at 4:59:24 pm

Oyvind :

why the gain and not the gamma ?
i think have to be overall aond not only one part of the image (such as gain)

g

Davinci Resolve Control Surface
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GTX470+GTX470+GTX285
24GB RAM
HP Dreamcolor
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Oyvind Stiauren
Re: How technically Emulate a Temperature/Tint tool
on Oct 27, 2011 at 5:56:20 pm

[Gabriele Turchi] "why the gain and not the gamma ?
i think have to be overall aond not only one part of the image (such as gain)"


Gain adjusts the white point while keeping the black the same. That is exactly what white point correction is.

If you adjust the gamma, you'll keep the black and the white the same white stretching the mid-tones.

Because of non-linearities is most images you'll often have to use a combination of gain, gamma and even blacks corrections to achieve a balanced white point correction. But if you just want to move the white point you'll have to use the gain control.

--
Oyvind Stiauren
Post production supervisor, Colorist
Terminal

Mexico City


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Mike Most
Re: How technically Emulate a Temperature/Tint tool
on Oct 28, 2011 at 5:25:48 am

>I just would like to add that moving the gain trackball along the correct axis effectively does the same >thing as Mike describes above.

No, it really doesn't. Not only does the gain control have a range limitation (it has its pivot at 0, but the control range is not linear), it only controls the upper level limit of each of the three channels. What I was describing is a situation where the original image has its colors misbalanced across the luminance range, not just in the upper regions. In that situation, some of the information that should have been in the red channel in the first place has been improperly assigned to the blue channel. So by subtracting some of that information in the blue channel and reassigning it to the red channel - where it actually belongs - you're accomplishing something a gain control cannot do, which is taking the information across all luminance levels from one channel and placing it in another. The result may appear similar in come cases, but in the case I was describing, a gain change would not solve the underlying problem.


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Oyvind Stiauren
Re: How technically Emulate a Temperature/Tint tool
on Oct 31, 2011 at 6:11:46 pm

[Mike Most] "No, it really doesn't"

You're right. I was mistakenly reading that you subtracted blue in the blue channel and added red in the red. My bad.

The component sliders in the color mixer are gain sliders though, with the pivot at 0, but with the added feature that they're mixed together on the output. You can easily see that on a parade scope.

--
Oyvind Stiauren
Post production supervisor, Colorist
Terminal

Mexico City


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