How to transform color image to grayscale in java

Question

How can I transform color image to grayscale using java code?

A sample grayscale image for reference:

Answer 1

A simplest way is to draw to GRAY buffered image

BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);  
Graphics g = image.getGraphics();  
g.drawImage(colorImage, 0, 0, null);  
g.dispose(); 

See more ways here