Generate Color Gradient in C#

Question

My question here is similar to the question here, except that I am working with C#.

I have two colors, and I have a predefine steps. How to retrieve a list of Colors that are the gradients between the two?

This is an approach that I tried, which didn't work:

int argbMax = Color.Chocolate.ToArgb();
int argbMin = Color.Blue.ToArgb();
var colorList = new List<Color>();

for(int i=0; i<size; i++)
{
    var colorAverage= argbMin + (int)((argbMax - argbMin) *i/size);
    colorList.Add(Color.FromArgb(colorAverage));
}

If you try the above code, you will find that a gradual increase in argb doesn't correspond to a visual gradual increase in the color.

Any idea on this?

Answer 1

    public static List<Color> GetGradientColors(Color start, Color end, int steps)
    {
        return GetGradientColors(start, end, steps, 0, steps - 1);
    }

    public static List<Color> GetGradientColors(Color start, Color end, int steps, int firstStep, int lastStep)
    {
        var colorList = new List<Color>();
        if (steps <= 0 || firstStep < 0 || lastStep > steps - 1)
            return colorList;

        double aStep = (end.A - start.A) / steps;
        double rStep = (end.R - start.R) / steps;
        double gStep = (end.G - start.G) / steps;
        double bStep = (end.B - start.B) / steps;

        for (int i = firstStep; i < lastStep; i++)
        {
            var a = start.A + (int)(aStep * i);
            var r = start.R + (int)(rStep * i);
            var g = start.G + (int)(gStep * i);
            var b = start.B + (int)(bStep * i);
            colorList.Add(Color.FromArgb(a, r, g, b));
        }

        return colorList;
    }

Answer 2

You will have to extract the R, G, B components and perform the same linear interpolation on each of them individually, then recombine.

int rMax = Color.Chocolate.R;
int rMin = Color.Blue.R;
// ... and for B, G
var colorList = new List<Color>();
for(int i=0; i<size; i++)
{
    var rAverage = rMin + (int)((rMax - rMin) * i / size);
    var gAverage = gMin + (int)((gMax - gMin) * i / size);
    var bAverage = bMin + (int)((bMax - bMin) * i / size);
    colorList.Add(Color.FromArgb(rAverage, gAverage, bAverage));
}

Answer 3

Maybe this function can help:

public IEnumerable<Color> GetGradients(Color start, Color end, int steps)
{
    Color stepper = Color.FromArgb((byte)((end.A - start.A) / (steps - 1)),
                                   (byte)((end.R - start.R) / (steps - 1)),
                                   (byte)((end.G - start.G) / (steps - 1)),
                                   (byte)((end.B - start.B) / (steps - 1)));

    for (int i = 0; i < steps; i++)
    {
        yield return Color.FromArgb(start.A + (stepper.A * i),
                                    start.R + (stepper.R * i),
                                    start.G + (stepper.G * i),
                                    start.B + (stepper.B * i));
    }
}

Answer 4

Use double instead of int:

double stepA = ((end.A - start.A) / (double)(steps - 1));
double stepR = ((end.R - start.R) / (double)(steps - 1));
double stepG = ((end.G - start.G) / (double)(steps - 1));
double stepB = ((end.B - start.B) / (double)(steps - 1));

and:

yield return Color.FromArgb((int)start.A + (int)(stepA * step),
                                            (int)start.R + (int)(stepR * step),
                                            (int)start.G + (int)(stepG * step),
                                            (int)start.B + (int)(stepB * step));

Answer 5

Oliver's answer was very close... but in my case some of my stepper numbers needed to be negative. When converting the stepper values into a Color struct my values were going from negative to the higher values e.g. -1 becomes something like 254. I setup my step values individually to fix this.

public static IEnumerable<Color> GetGradients(Color start, Color end, int steps)
{
    int stepA = ((end.A - start.A) / (steps - 1));
    int stepR = ((end.R - start.R) / (steps - 1));
    int stepG = ((end.G - start.G) / (steps - 1));
    int stepB = ((end.B - start.B) / (steps - 1));

    for (int i = 0; i < steps; i++)
    {
        yield return Color.FromArgb(start.A + (stepA * i),
                                    start.R + (stepR * i),
                                    start.G + (stepG * i),
                                    start.B + (stepB * i));
    }
}