图像处理之颜色梯度变化 (Color Gradient)

有过UI设计经验的一定对2D图形渲染中的Color Gradient 或多或少有些接触，很多编程

语言也提供了Gradient的接口，但是想知道它是怎么实现的嘛？

本文介绍三种简单的颜色梯度变化算法，就可以很容易实现常见的梯度变化算法

三种都要求提供两个参数即起始颜色RGB值, 最终颜色RGB的值。

垂直梯度颜色变化，效果如下：

水平梯度颜色变化，效果如下：

水平与垂直两个方向叠加梯度变化效果如下：

算法代码及其解释

计算起始颜色和终点颜色RGB之间差值代码如下：

float rr = startColor[0] - endColor[0];

float gg = startColor[1] - endColor[1];

float bb = startColor[2] - endColor[2];

实现垂直梯度变化的代码如下：

r = endColor[0] + (int)(rr * ((float)row/255.0f) +0.5f);

g = endColor[1] + (int)(gg * ((float)row/255.0f) +0.5f);

b = endColor[2] + (int)(bb * ((float)row/255.0f) +0.5f);

实现水平梯度变化代码如下：

// set gradient color valuefor each pixel

r = endColor[0] + (int)(rr * ((float)col/255.0f) +0.5f);

g = endColor[1] + (int)(gg * ((float)col/255.0f) + 0.5f);

b = endColor[2] + (int)(bb * ((float)col/255.0f) +0.5f);

实现水平和垂直两个方向上Gradient叠加代码如下：

r = endColor[0] + (int)(rr * (((float)col * (float)row)/size) +0.5f);

g = endColor[1] + (int)(gg * (((float)col * (float)row)/size) +0.5f);

b = endColor[2] + (int)(bb * (((float)col * (float)row)/size) +0.5f);

程序对上面三种Gradient方法分别放在三个不同的方法中，根据参数调用。

程序的完全Java源代码如下：

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;

import javax.swing.JComponent;
import javax.swing.JFrame;

public class ColorGradientDemo extends JComponent {

	/**
	 * 
	 */
	private static final long serialVersionUID = -4134440495899912869L;
	private BufferedImage image = null;
	
	protected void paintComponent(Graphics g) {
		Graphics2D g2 = (Graphics2D)g;
		g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
		g2.drawImage(getImage(4), 5, 5, image.getWidth(), image.getHeight(), null);
	}
	
	public BufferedImage getImage(int type) {
		if(image == null) {
			image = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);
			int[] rgbData = new int[256*256];
			if(type == 1) {
				generateVGradientImage(rgbData);
			} else if(type == 2) {
				generateHGradientImage(rgbData);
			} else {
				generateHVGradientImage(rgbData);
			}
			setRGB(image, 0, 0, 256, 256, rgbData);
		}
		return image;
	}

	private void generateVGradientImage(int[] rgbData) {
		int[] startColor = getStartColor();
		int[] endColor = getEndColor();
		
		float rr = startColor[0] - endColor[0];
		float gg = startColor[1] - endColor[1];
		float bb = startColor[2] - endColor[2];
		
		int a=255;
		int r=0, g=0, b=0;
		int index = 0;
		for(int row=0; row<256; row++) {
			for(int col=0; col<256; col++) {
				// set random color value for each pixel
				// set gradient color value for each pixel
				r = endColor[0] + (int)(rr * ((float)row/255.0f) + 0.5f);
				g = endColor[1] + (int)(gg * ((float)row/255.0f) + 0.5f);
				b = endColor[2] + (int)(bb * ((float)row/255.0f) + 0.5f);
				
				rgbData[index] = ((a & 0xff) << 24) |
								((r & 0xff) << 16)  |
								((g & 0xff) << 8)   |
								((b & 0xff));
				index++;
			}
		}
	}
	
	private void generateHGradientImage(int[] rgbData) {
		int[] startColor = getStartColor();
		int[] endColor = getEndColor();
		
		float rr = startColor[0] - endColor[0];
		float gg = startColor[1] - endColor[1];
		float bb = startColor[2] - endColor[2];
		
		int a=255;
		int r=0, g=0, b=0;
		int index = 0;
		for(int row=0; row<256; row++) {
			for(int col=0; col<256; col++) {
				
				// set gradient color value for each pixel
				r = endColor[0] + (int)(rr * ((float)col/255.0f) + 0.5f);
				g = endColor[1] + (int)(gg * ((float)col/255.0f) + 0.5f);
				b = endColor[2] + (int)(bb * ((float)col/255.0f) + 0.5f);
				
				rgbData[index] = ((a & 0xff) << 24) |
								((r & 0xff) << 16)  |
								((g & 0xff) << 8)   |
								((b & 0xff));
				index++;
			}
		}
	}
	
	private void generateHVGradientImage(int[] rgbData) {
		int[] startColor = getStartColor();
		int[] endColor = getEndColor();
		
		float rr = startColor[0] - endColor[0];
		float gg = startColor[1] - endColor[1];
		float bb = startColor[2] - endColor[2];
		
		int a=255;
		int r=0, g=0, b=0;
		int index = 0;
		float size = (float)Math.pow(255.0d, 2.0);
		for(int row=0; row<256; row++) {
			for(int col=0; col<256; col++) {
				// set random color value for each pixel
				r = endColor[0] + (int)(rr * (((float)col * (float)row)/size) + 0.5f);
				g = endColor[1] + (int)(gg * (((float)col * (float)row)/size) + 0.5f);
				b = endColor[2] + (int)(bb * (((float)col * (float)row)/size) + 0.5f);
				
				rgbData[index] = ((a & 0xff) << 24) |
								((r & 0xff) << 16)  |
								((g & 0xff) << 8)   |
								((b & 0xff));
				index++;
			}
		}
	}
	
	public int[] getStartColor() {
		return new int[]{246,53,138};
	}
	
	public int[] getEndColor() {
		return new int[]{0,255,255};
	}
	
	public void setRGB( BufferedImage image, int x, int y, int width, int height, int[] pixels ) {
		int type = image.getType();
		if ( type == BufferedImage.TYPE_INT_ARGB || type == BufferedImage.TYPE_INT_RGB )
			image.getRaster().setDataElements( x, y, width, height, pixels );
		else
			image.setRGB( x, y, width, height, pixels, 0, width );
    }
	
	public static void main(String[] args) {
		JFrame frame = new JFrame("Gradient Color Panel");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.getContentPane().setLayout(new BorderLayout());
		
		// Display the window.
		frame.getContentPane().add(new ColorGradientDemo(), BorderLayout.CENTER);
		frame.setPreferredSize(new Dimension(280,305));
		frame.pack();
		frame.setVisible(true);
	}

}