c++ - How to interpolate a color sequence?

Question

I need to interpolate or change gradually a sequence of colors, so it goes from colorA to colorB to colorC to colorD and them back to colorA, this need to be based on time elapsed in milliseconds, any help will be much appreciated (algorithms, pseudo code will be great).

Note that I am working with RGB, it could be 0-255 or 0.0-1.0 range.

This is what I have so far, I need to change the colors on every "timePeriod", them I calculate the percentage of time elapsed and change the colors, the problem with this code is that there is a jump when it goes from A to B to B to C and so on

int millisNow = ofGetElapsedTimeMillis();
int millisSinceLastCheck = millisNow - lastTimeCheck;
if ( millisSinceLastCheck > timePeriod ) {
    lastTimeCheck = millisNow;
    millisSinceLastCheck = 0;
    colorsIndex++;
    if ( colorsIndex == colors.size()-1 ) colorsIndex = 0;
    cout << "color indes: " << colorsIndex << endl;
    cout << "color indes: " << colorsIndex + 1 << endl;
}
timeFraction = (float)(millisSinceLastCheck) / (float)(timePeriod);
float p = timeFraction;
colorT.r = colors[colorsIndex].r * p + ( colors[colorsIndex+1].r * ( 1.0 - p ) );
colorT.g = colors[colorsIndex].g * p + ( colors[colorsIndex+1].g * ( 1.0 - p ) );
colorT.b = colors[colorsIndex].b * p + ( colors[colorsIndex+1].b * ( 1.0 - p ) );
colorT.normalize();

Thanks in advance

Answer 1

Your code is mostly correct, but you are doing the interpolation backwards: i.e. you are interpolating B->A, then C->B, then D->C, etc. This causes the discontinuity when switching colors.

You should replace this:

colorT.r = colors[colorsIndex].r * p + ( colors[colorsIndex+1].r * ( 1.0 - p ) );

with:

colorT.r = colors[colorsIndex].r * (1.0 - p) + ( colors[colorsIndex+1].r * p );

and the same for the other lines.

Also, as others have said, using a different color space than RGB can provide better looking results.