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); 	}  }

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