Colormaps in JAVA images

In my previous post I showed how to dinamically create a JPEG from a java array.

The problem with these approach is that the color is not very intuitive.
Now I want to create a suitable colormap for the image.


The first colormap will be rainbow. We create this colormap working with HSB, we will change the hue and leave the brightness and saturation at a fixed value.

public static BufferedImage generateImage(double[][] data, int pixelsWidth, int pixelsHeight ) throws Exception{

        double x =0,y = 0;
        BufferedImage bi = new BufferedImage( pixelsWidth, pixelsHeight,  BufferedImage.TYPE_3BYTE_BGR );
        Graphics2D g=(Graphics2D)bi.getGraphics();

        int w=data[0].length;
        int l=data.length;
        double Dy=(double)pixelsHeight/(double)l;
        double Dx=(double)pixelsWidth/(double)w;
        int height = (int)Math.ceil(Dy);
        int width = (int)Math.ceil(Dx);	
        int gap=(int)Math.ceil(width/4);
    	double max=-Double.MAX_VALUE;
    	double min=Double.MAX_VALUE;
    	for (int i=0;i<l;i++){
    		for (int j=0;jmax) max=data[i][j];
    			if (data[i][j]<min) min=data[i][j];
        float fcolor;
        float saturation=(float)0.9;
        float bright=(float)0.7;
        g.setColor( Color.WHITE);
        g.fillRect( 0, 0 , pixelsWidth,pixelsHeight); 
        for( int i =0; i < l; i++ ){        	
            for( int j =0; j < w; j++ ){            	
           	g.setColor(Color.getHSBColor(hue*0.7, saturation, bright));             		                  
                g.fillRect( (int)x, (int)y , width-gap,height);        

        return bi;

I multiply the hue by 0.7 to magnify the difference between the greater and smaller value because hue=1 and hue=0 are almost the same color.

This is an example of this colormap:

Dark body radiator

This colormap fixes the hue and changes the saturation and brightness. It is easily created from the previous one with the next change:

g.setColor(Color.getHSBColor((float)0.2, (float)Math.sqrt(1-fcolor), fcolor));

An example of this colormap is:


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