Add Vs Brightness?

Compositing
1

so according to the 3.5 manual, add and brightness are described as "atomic" level functions:

QUOTE
Atomic-Level Functions These nodes are described as atomic-level because they each apply a single mathematical  operation. Due to their simplicity, they are very easy to work with. They are also ideal for use  on the command line.

Add
The Add function adds color to the R, G, B, A, or Z channels. This adds color to black areas,  including those beyond the image frame, in case you move the image later. Any correction  that occurs outside of the DOD can be corrected with the SetBGColor node. Shake

2

Add simplys adds to the values.

Brightness multiplies. It's essentially a Mult that works across RGB in one shot.

3

QUOTE(deepstructure @ 10/05/05, 02:52 PM)
so according to the 3.5 manual, add and brightness are described as "atomic" level functions:
i normally change density value by using an add node (i work with cineon log files) and simply increasing .0225, .03, .045, etc., across the board.  this both keeps the changes i make consistent and approximates the filmic equivalent of stops. 

in reading the documentation, i would assume the add node used this way and the brightness node would create the same density change - but they don't.  the brightness node seems to create a different curve and introduce a contrast change.  can anyone explain how this works?
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I hope you're not one of those freaks who color corrects in log space. That only works if you're tweaking a lut (adjusting curves).

linearize (and promote to float) your cineons,and mults behave in a way that's analogous to stops

an add node simply adds the value you enter to the value of the pixel.

4

QUOTE(alanb @ 10/10/05, 04:06 PM)
I hope you're not one of those freaks who color corrects in log space. That only works if you're tweaking a lut (adjusting curves).

linearize (and promote to float) your cineons,and mults behave in a way that's analogous to stops

an add node simply adds the value you enter to the value of the pixel.
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lol. A way to check the CC node is to throw a horizontal ramp down and use the PlotScanline Viewer Script or node.

And: an Add in Log = a Mult/Brightness in Linear. Strange but True facts I saw on the cover of The World Weekly News...

Ramp -> LogLin (to Log) -> Add -> LogLin (to Lin):

Ramp1 = Ramp(512, 512, 1, 1, 0.5, 0, 0, 0, 1, 0, 1, 1, 1, 1,
0);
LogLin1 = LogLin(Ramp1, 1, 0, 0, 0, 95, rBlack, rBlack, 685,
rWhite, rWhite, 0.6, rNGamma, rNGamma, 1.7, rDGamma, rDGamma,
0, rSoftClip, rSoftClip);
Add1 = Add(LogLin1, -0.07, -0.08, -0.08, 0, 0);
LogLin2 = LogLin(Add1, 0, 0, 0, 0, 95, rBlack, rBlack, 685, rWhite,
rWhite, 0.6, rNGamma, rNGamma, 1.7, rDGamma, rDGamma, 0,
rSoftClip, rSoftClip);
PlotScanline1 = PlotScanline(LogLin2, 512, 512, 0);

What's nice here is that you can use this in a linear CC node without pain since it concatenates. Though, why you'd want to since its a Mult, is up to you to answer.

-eugene