jirko

Can someone give me some details about the math behind the scale object?

Can someone give me some details about the math behind the scale object?
Thanks!


math-behind-scale

I don't have access to the scale source code, but I can make a guess.

- Subtract the low input value from the number, then divide the result by the difference between high input value and low input value. This gives you a number between 0 and 1.

- Then multiply this again with the difference between low output and high output value, and finally add the low output value.

As an expression, this would look like this:

expr "(($f1-$f2)/($f3-$f2)) * ($f5-$f4) + $f4"

$f1 being your number input, $f1 the low input value, $f2 the high input value, $f3 the low output value, $f4 the high output value.

This still ignores the exponential part, but I don't think this should be too hard to figure out as well.

eh, I'm silly. Should have looked into the documentation of [scale] first where the formula is written down. So that's what you should do as well!

expr "(($f1-$f2)/($f3-$f2)) * ($f5-$f4) + $f4"
$f1 being your number input, $f1 the low input value, $f2 the high input value, $f3 the low output value, $f4 the high output value.

eh, I'm silly. Should have looked into the documentation of [scale] first where the formula is written down. So that's what you should do as well!


it says "a,b and c are the three typed-in arguments".

So c is the exponential factor and e is the base of the natural logarithm.

it says "a,b and c are the three typed-in arguments".
So c is the exponential factor and e is the base of the natural logarithm.
But what's a and b ??


Woops, I didn't now that the formula is inside the docs.

I think that what is written in the docs is for exponential mode calculations. I was interested as well to use a jit.expr expression that simulates the scale object.

I managed to do something similar to [scale 0 255 -1. 1.] with the following expresion

but I don't have a clue how to do [scale 0 255 1. -1.]

Does anyone know? I'm not good at maths either

I managed to do something similar to [scale 0 255 -1. 1.] with the following expresion 

Does anyone know? I'm not good at maths either


Please, if anyone knows how to reverse a scale in jit.expr. I am trying to reverse a short matrix with 2d xy coordinates for a 640x480 pixels to have 3d xy coordinates which are -1. 1. for both x and y (with the center as 0.).

I did the first part for the x coordinate where 0 becomes -1. and 640 becomes 1. But for the y value, 0 is 1. and 480 is -1.

So I would need an expresion for jit.expr to turn a (-1. 1) matrix the other way around (1. -1.)

I did the first part for the x coordinate where 0 becomes -1. and 640 becomes 1. But for the y value, 0 is 1. and 480 is -1.   

Could you just multiply by -1. after the scale?

I guess it's mid school mathematics! I'm loosing my mind!!

math behind scale?