Creating A Centered Gradient

[user_deleted]

Hello,

sorry for this seemingly simple question:
I am trying to create a ramp going left to right from black to white to black. I did this by using two gradient nodes, inverting the values of the second and then combining both with an imult:

Ramp1 = Ramp(960, 1080, 2, 1, 0.1, 0, 0, 0, 1, 0, 1, 1, 1, 1,0);
Ramp2 = Ramp(960, 1080, Ramp1.bytes, Ramp1.orientation, 1-Ramp1.center, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0);
IMult1 = IMult(Ramp1, Ramp2, 1, 100, 0);

The result looks much more pronounced to the left side, its more apparent the further you shift the center of the first gradient towards zero. Why is that? I want a centered white beam feathering off to the sides. Now on the right there is more black then on the left.
This must be simple...
Shake4 on 10.4.10

[user_deleted]

try this:

CODE
Ramp1 = Ramp(960, 1080, 2, 1, 0.213, 0, 0, 0, 1, 0, 1, 1, 1,
    1, 0);
Flop1 = Flop(Ramp1);
IMult1 = IMult(Ramp1, Flop1, 1, 100, 0);

or depending what you're looking for, something like this:

CODE
Ramp1 = Ramp(960, 1080, 2, 1, 0.082, 0, 0, 0, 1, 0, 1, 1, 1,
    1, 0);
Flop1 = Flop(Ramp1);
Pan1 = Pan(Flop1, width, 0, 0, 0.5, 0);
CCrop2 = CCrop(Pan1, 0, 0, width*2, height);
IAdd1 = IAdd(Ramp1, CCrop2, 1, 100);

or yet another way:

CODE
RGrad1 = RGrad(960, 1080, 2, width/2, height/2, 1, 1, 500, 0.5,
    1, 1, 1, 1, 0, 0, 0, 0, 0, 0);
Move2D1 = Move2D(RGrad1, 0, 0, 0, 1, 1, 1000, 0, 0, width/2,
    height/2, "default", xFilter, "trsx", 0, 0, 0.5, 0, 0, time);
SetDOD1 = SetDOD(Move2D1, 0, width, 0, height);

[user_deleted]

Thanks alot zem!
All your suggestions work wonderfully. How simple

Nonetheless, maybe someone could explain to me why my first attempt didnt work as i expected? Where was the fault?

Thanks again.

[user_deleted]

hiya,

glad it helped..

the problem with your approach was that you linked the "center" parameter of the ramp but switched the beginning and end color... so obviously when you told the Ramp1 center to shift more towards color1 (ie black), the linked Ramp2 was shifting towards color1 too (ie white) resulting in an asymmetrical multiplication. or at least that's what i thought

++ chris

[user_deleted]

try this:

CODE
ColorX1 = ColorX(0, {{ float pi=3.14159265; asin( fabs(sin(pi*x/width)) ) / (0.5*pi); }}, g, b, a, z);

or this with an extra variable to control the spikecount

CODE
ColorX1 = ColorX(0, {{ float pi=3.14159265; asin( fabs(sin(spikes*pi*x/width)) ) / (0.5*pi); }}, g, b, a, z, float spikes = 7);

do.QUOTE

[user_deleted]

Hi zuao,

thanks for your reply, this also works great.
In the meantime, i figured my original approach didnt work because the Ramp function doesnt create a linear ramp. So combining it with itself wont result in a centered gradient. Or thats how it seems to me.
Thanks again.

[user_deleted]

well, as far is i can see the ramp node generates a perfectly linear gradient, but the center value is not symetrical, so using a 1-ramp1.center parameter messes up the result.

for example this works just fine...

CODE
Ramp1 = Ramp(960, 1080, 4, 1, 0.5, 0, 0, 0, 1, 0, 1, 1, 1, 1,
    0);
Ramp2 = Ramp(960, 1080, Ramp1.bytes, Ramp1.orientation, 0.5,
    1, 1, 1, 1, 0, 0, 0, 0, 1, 0);
IMult1 = IMult(Ramp1, Ramp2, 1, 100, 0);
Gamma2 = Gamma(IMult1, 0.8, rGamma, rGamma, 1);
Brightness1 = Brightness(Gamma2, 4.4);
PlotScanline1 = PlotScanline(Brightness1, width, 512, 0);

of course you could replace the gamma and brightness node by a lookuptable for better control.
++ chris