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What is lerp in general?

So as the titel says, I constantly get to see this lerp thing that gets used heavily within materials. But what exactly is it, what does the term lerp define?

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asked Dec 23 '14 at 12:01 AM in Using UE4

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2 answers: sort voted first

Lerp is slang for Linear Interpolate. Given two different inputs A and B, think of a straight line drawn between them - with the Alpha node saying how far along that line you are.

For example, lets say you have a red color [1,0,0] in A - and a blue color [0,0,1] in B. If you set the Alpha to 0.5 (50%), then the Lerp will output a dark purplish color [0.5,0,0.5] - or halfway between each of the X Y and Z components linearly (and independently btw - hence the loss in brightness in this example).

They're great for mixing two materials together. Also very handy for masking out parts of your mesh. Let's say you feed the Alpha with an actual mask texture - wherever there is white you'll get one input and where there is black you'll get the other. Use greys for blending. But anyways, that's the general idea.

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answered Dec 23 '14 at 12:19 AM

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avatar image JorisCeoen Dec 23 '14 at 03:04 PM

Hey man, thanks a whole lot. This made me understand it and makes me understand most of the structures in the starter's content material creations!

avatar image NLEGITN Jan 28 '15 at 11:31 PM

I thought this was also very informative! Let's say you have a green sewer texture and a lava texture right next to each other. Could you use Lerp and a black and white mask to make the black the sewer texture and the white the lava texture??

avatar image ddsol Dec 17 '15 at 07:58 PM

Your comment and independently btw - hence the loss in brightness in this example is incorrect. The reason it's darker is mostly because of the standard gamma of ~2.2. A value of 50% brightness in the computer translates to about 22% brightness on the monitor, which is much less than 50%. sRGB colors, in particular, are very bad candidates for lerping. Modern graphics hardware can correct for these issues.

avatar image ymars STAFF Apr 30 '16 at 03:00 AM
avatar image DisplaySweet Sep 15 '17 at 02:34 AM

... an example on how to use it in different scenario than materials: https://www.youtube.com/watch?v=Fa8Cg6Q9bLY

avatar image Jakoban Jun 23 '18 at 09:20 AM

Say isn't that what blend does?

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so what.. LERP = FALL OFF like in 3dsmax nodes? or just a Blend?

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answered Jun 03 '19 at 05:24 PM

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