How to convert RGB color to grayscale in Java

I’m trying to create a method that converts a given java.awt.Color color to grayscale. Here’s what I have right now:

public Color gs(Color col) {
        if (grayScale) {
            float[] rgb = col.getRGBColorComponents(new float[3]);
            rgb[0] = rgb[1] = rgb[2] = (int)(0.299 * rgb[0] + 0.587 * rgb[1] + 0.114 * rgb[2]);
            col = new Color(rgb[0], rgb[1], rgb[2]);
        }
        return col;
}

However, when I call this method, it seems to be returning the color black every single time, regardless of the input color. How do I fix this?

Answer

The float components are in the range of [0.0, 1.0]. You are adding the scaled RGB components together and then casting them to int:

rgb[0] = rgb[1] = rgb[2] = (int)(0.299 * rgb[0] + 0.587 * rgb[1] + 0.114 * rgb[2]);
                            ^^^ Cast to int

You would get the color black if all of the values in the rgb array are zero. This is most likely because the cast to int truncates the resulting floating-point values down to zero. Since rgb is an array of floats, you should cast result to float.

rgb[0] = rgb[1] = rgb[2] =  (float)(0.299 * rgb[0] + 0.587 * rgb[1] + 0.114 * rgb[2]);
                           ^ Key change, cast to float