Topic: Calculate RGB values between two colours

Okay, say I've got two colour points in the RGB scale, one representing an eye-searing red, the other a mid-level dark green, and I need to calculate 10 evenly-spaced points between them, does anyone know a way I could do this? See, it's part of a java assignment I'm doing, that colours JList item backgrounds dependent on a given value. 12 points in total, including the two extremes. I can do the program, I just don't know how to calculate those points to create the appropaite Color objects for them.


Justice 4 Pat Richard

How about just dividing the distance for the channels seperatly by 12, then
adding rdifference / 10 to r, etc for each point?

I don't know if that'l look even though.

Well, the transition from a mid-dark green also involves dropping the blue channel, since that's what makes the green darker. And since the correct transition goes through green to yellow to orange to red...


Justice 4 Pat Richard

In that case, I'm pretty sure RGB won't do for you, you will need to convert into another color space.

Yes... apparently HSV should be able to do it, but I've still got to work the algorithm out


Justice 4 Pat Richard

(Edited by Skaarjj on 10-14-2006 10:05)

How about vectors?

// starting values
v1x, v1y, v1z
v2x, v2y, v2z

// delta between the xyz axis
dx=v2x-v1x
dy=v2y-v1y
dz=v2z-v1z

// pythagoras to get the distance
distance = sqr( dx*dx + dy*dy + dz*dz )

// get the unit vectors
ux=dx/distance
uy=dy/distance
uz=dz/distance

Once you have the unit vectors and distance, just a matter of dividing, multiplying, and adding it up like TP said.

mult=distance/12.0
for(i==1;i>10;i++){
newx=v1x+ux*i*mult
newy=v1y+uy*i*mult
newz=v1z+uz*i*mult
}

Ahhh... something like that.

Bit of a long way compared to what TP said, but this is how I would go about it. No real reason other than being a freak for vectors. They are just so much fun to play with.

Skaarj: HSV <-> RGB conversions are well documented. Check wikipedia: HSV_color_space or wikipedia: HSL_color_space. I doubt using either HSL or HSV would make any difference in the end result.

warjournal: your for(...) statement is borked. It should read: for( i=0; i<10; i++ ) Also there is no need for the 1 add and 1 mul per coordinate. One add is enough. Though it's not as if it would matter with only 10 iterations.



(Edited by poi on 10-14-2006 16:14)