当图片很大的时候，要生成预览图来提高网站响应速率，采用java的image相关类来生成缩略图
package com.liuc.core;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
import com.liuc.config.ImageSizeConfig;
import com.liuc.util.UUIDUtil;
/**
*
* @brief ThumbnailUtil.java 生成缩略图
*/
public class ThumbnailUtil {
/**
* 宽度
*/
private int width;
/**
* 高度
*/
private int height;
private int scaleWidth;
double support = (double) 3.0;
double PI = (double) 3.14159265358978;
double[] contrib;
double[] normContrib;
double[] tmpContrib;
int startContrib, stopContrib;
int nDots;
int nHalfDots;
/** *//**
* Start: Use Lanczos filter to replace the original algorithm for image
* scaling. Lanczos improves quality of the scaled image modify by :blade
*/
public static void main(String[] args) {
ThumbnailUtil is = new ThumbnailUtil();
try {
is.compressImageAsJpg(new File("D:/123/1.jpg"), new File("D:/123/1111.jpg"), 765, 129);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public File compressImgByAssignMinBoundLength(File inFile, ImageSizeConfig pc) throws Exception{
try {
Image img = ImageIO.read(inFile);
int width = img.getWidth(null);
int height = img.getHeight(null);
int OutputWidth = pc.getWidth();
int OutputHeight = pc.getHeight();
int new_w,new_h;
if (height <= OutputWidth && width <= OutputHeight) {// 不压缩
new_w = width;
new_h = height;
} else if (height > width) {// 已宽为准
new_w = OutputWidth;
new_h = (int) (new_w / ((double) width / (double) height));
} else {// 已高为准
new_h = OutputHeight;
new_w = (int) ((new_h * (double) width / (double) height));
}
String fileName = UUIDUtil.getUUID() + pc.getExt();
File tmpFile = new File("D:/123", fileName);
compressImageAsJpg(inFile, tmpFile, new_w, new_h);
return tmpFile;
} catch (Exception e) {
throw new Exception("compress img error.", e);
}
}
/**
* 压缩图片
* @param fromFileStr
* @param saveToFileStr
* @param formatWideth
* @param formatHeight
* @throws Exception
*/
public void compressImageAsJpg(File fromFile, File saveToFile,
int formatWideth, int formatHeight) throws Exception{
try {
saveImageAsJpg(fromFile, saveToFile, formatWideth, formatHeight);
} catch (Exception e) {
throw new Exception("compress img error.", e);
}
}
// fromFileStr原图片地址,saveToFileStr生成缩略图地址,formatWideth生成图片宽度,formatHeight高度
public void saveImageAsJpg(File inputFile, File saveToFile,
int formatWideth, int formatHeight) throws Exception {
BufferedImage srcImage;
File saveFile = saveToFile;
File fromFile = inputFile;
srcImage = javax.imageio.ImageIO.read(fromFile); // construct image
int imageWideth = srcImage.getWidth(null);
int imageHeight = srcImage.getHeight(null);
int changeToWideth = 0;
int changeToHeight = 0;
if (imageWideth > 0 && imageHeight > 0) {
// flag=true;
if (imageWideth / imageHeight >= formatWideth / formatHeight) {
if (imageWideth > formatWideth) {
changeToWideth = formatWideth;
changeToHeight = (imageHeight * formatWideth) / imageWideth;
} else {
changeToWideth = imageWideth;
changeToHeight = imageHeight;
}
} else {
if (imageHeight > formatHeight) {
changeToHeight = formatHeight;
changeToWideth = (imageWideth * formatHeight) / imageHeight;
} else {
changeToWideth = imageWideth;
changeToHeight = imageHeight;
}
}
}
srcImage = imageZoomOut(srcImage, changeToWideth, changeToHeight);
ImageIO.write(srcImage, "JPEG", saveFile);
}
public BufferedImage imageZoomOut(BufferedImage srcBufferImage, int w, int h) {
width = srcBufferImage.getWidth();
height = srcBufferImage.getHeight();
scaleWidth = w;
if (DetermineResultSize(w, h) == 1) {
return srcBufferImage;
}
CalContrib();
BufferedImage pbOut = HorizontalFiltering(srcBufferImage, w);
BufferedImage pbFinalOut = VerticalFiltering(pbOut, h);
return pbFinalOut;
}
/**
* 决定图像尺寸
*/
private int DetermineResultSize(int w, int h) {
double scaleH, scaleV;
scaleH = (double) w / (double) width;
scaleV = (double) h / (double) height;
// 需要判断一下scaleH，scaleV，不做放大操作
if (scaleH >= 1.0 && scaleV >= 1.0) {
return 1;
}
return 0;
} // end of DetermineResultSize()
private double Lanczos(int i, int inWidth, int outWidth, double Support) {
double x;
x = (double) i * (double) outWidth / (double) inWidth;
return Math.sin(x * PI) / (x * PI) * Math.sin(x * PI / Support)
/ (x * PI / Support);
}
private void CalContrib() {
nHalfDots = (int) ((double) width * support / (double) scaleWidth);
nDots = nHalfDots * 2 + 1;
try {
contrib = new double[nDots];
normContrib = new double[nDots];
tmpContrib = new double[nDots];
} catch (Exception e) {
System.out.println("init contrib,normContrib,tmpContrib" + e);
}
int center = nHalfDots;
contrib[center] = 1.0;
double weight = 0.0;
int i = 0;
for (i = 1; i <= center; i++) {
contrib[center + i] = Lanczos(i, width, scaleWidth, support);
weight += contrib[center + i];
}
for (i = center - 1; i >= 0; i--) {
contrib[i] = contrib[center * 2 - i];
}
weight = weight * 2 + 1.0;
for (i = 0; i <= center; i++) {
normContrib[i] = contrib[i] / weight;
}
for (i = center + 1; i < nDots; i++) {
normContrib[i] = normContrib[center * 2 - i];
}
} // end of CalContrib()
// 处理边缘
private void CalTempContrib(int start, int stop) {
double weight = 0;
int i = 0;
for (i = start; i <= stop; i++) {
weight += contrib[i];
}
for (i = start; i <= stop; i++) {
tmpContrib[i] = contrib[i] / weight;
}
} // end of CalTempContrib()
private int GetRedValue(int rgbValue) {
int temp = rgbValue & 0x00ff0000;
return temp >> 16;
}
private int GetGreenValue(int rgbValue) {
int temp = rgbValue & 0x0000ff00;
return temp >> 8;
}
private int GetBlueValue(int rgbValue) {
return rgbValue & 0x000000ff;
}
private int ComRGB(int redValue, int greenValue, int blueValue) {
return (redValue << 16) + (greenValue << 8) + blueValue;
}
// 行水平滤波
private int HorizontalFilter(BufferedImage bufImg, int startX, int stopX,
int start, int stop, int y, double[] pContrib) {
double valueRed = 0.0;
double valueGreen = 0.0;
double valueBlue = 0.0;
int valueRGB = 0;
int i, j;
for (i = startX, j = start; i <= stopX; i++, j++) {
valueRGB = bufImg.getRGB(i, y);
valueRed += GetRedValue(valueRGB) * pContrib[j];
valueGreen += GetGreenValue(valueRGB) * pContrib[j];
valueBlue += GetBlueValue(valueRGB) * pContrib[j];
}
valueRGB = ComRGB(Clip((int) valueRed), Clip((int) valueGreen),
Clip((int) valueBlue));
return valueRGB;
} // end of HorizontalFilter()
// 图片水平滤波
private BufferedImage HorizontalFiltering(BufferedImage bufImage, int iOutW) {
int dwInW = bufImage.getWidth();
int dwInH = bufImage.getHeight();
int value = 0;
BufferedImage pbOut = new BufferedImage(iOutW, dwInH,
BufferedImage.TYPE_INT_RGB);
for (int x = 0; x < iOutW; x++) {
int startX;
int start;
int X = (int) (((double) x) * ((double) dwInW) / ((double) iOutW) + 0.5);
int y = 0;
startX = X - nHalfDots;
if (startX < 0) {
startX = 0;
start = nHalfDots - X;
} else {
start = 0;
}
int stop;
int stopX = X + nHalfDots;
if (stopX > (dwInW - 1)) {
stopX = dwInW - 1;
stop = nHalfDots + (dwInW - 1 - X);
} else {
stop = nHalfDots * 2;
}
if (start > 0 || stop < nDots - 1) {
CalTempContrib(start, stop);
for (y = 0; y < dwInH; y++) {
value = HorizontalFilter(bufImage, startX, stopX, start,
stop, y, tmpContrib);
pbOut.setRGB(x, y, value);
}
} else {
for (y = 0; y < dwInH; y++) {
value = HorizontalFilter(bufImage, startX, stopX, start,
stop, y, normContrib);
pbOut.setRGB(x, y, value);
}
}
}
return pbOut;
} // end of HorizontalFiltering()
private int VerticalFilter(BufferedImage pbInImage, int startY, int stopY,
int start, int stop, int x, double[] pContrib) {
double valueRed = 0.0;
double valueGreen = 0.0;
double valueBlue = 0.0;
int valueRGB = 0;
int i, j;
for (i = startY, j = start; i <= stopY; i++, j++) {
valueRGB = pbInImage.getRGB(x, i);
valueRed += GetRedValue(valueRGB) * pContrib[j];
valueGreen += GetGreenValue(valueRGB) * pContrib[j];
valueBlue += GetBlueValue(valueRGB) * pContrib[j];
// System.out.println(valueRed+"->"+Clip((int)valueRed)+"<-");
//
// System.out.println(valueGreen+"->"+Clip((int)valueGreen)+"<-");
// System.out.println(valueBlue+"->"+Clip((int)valueBlue)+"<-"+"-->");
}
valueRGB = ComRGB(Clip((int) valueRed), Clip((int) valueGreen),
Clip((int) valueBlue));
// System.out.println(valueRGB);
return valueRGB;
} // end of VerticalFilter()
private BufferedImage VerticalFiltering(BufferedImage pbImage, int iOutH) {
int iW = pbImage.getWidth();
int iH = pbImage.getHeight();
int value = 0;
BufferedImage pbOut = new BufferedImage(iW, iOutH,
BufferedImage.TYPE_INT_RGB);
for (int y = 0; y < iOutH; y++) {
int startY;
int start;
int Y = (int) (((double) y) * ((double) iH) / ((double) iOutH) + 0.5);
startY = Y - nHalfDots;
if (startY < 0) {
startY = 0;
start = nHalfDots - Y;
} else {
start = 0;
}
int stop;
int stopY = Y + nHalfDots;
if (stopY > (int) (iH - 1)) {
stopY = iH - 1;
stop = nHalfDots + (iH - 1 - Y);
} else {
stop = nHalfDots * 2;
}
if (start > 0 || stop < nDots - 1) {
CalTempContrib(start, stop);
for (int x = 0; x < iW; x++) {
value = VerticalFilter(pbImage, startY, stopY, start, stop,
x, tmpContrib);
pbOut.setRGB(x, y, value);
}
} else {
for (int x = 0; x < iW; x++) {
value = VerticalFilter(pbImage, startY, stopY, start, stop,
x, normContrib);
pbOut.setRGB(x, y, value);
}
}
}
return pbOut;
} // end of VerticalFiltering()
int Clip(int x) {
if (x < 0)
return 0;
if (x > 255)
return 255;
return x;
}
}
package com.liuc.util;
import java.util.UUID;
public class UUIDUtil {
public static String getUUID() {
UUID uuid = UUID.randomUUID();
String str = uuid.toString();
// 去掉"-"符号
String temp = str.substring(0, 8) + str.substring(9, 13) + str.substring(14, 18) + str.substring(19, 23) + str.substring(24);
return str+","+temp;
}
}
package com.liuc.config;
public class ImageSizeConfig {
public int getWidth() {
return 320;
}
public int getHeight() {
return 240;
}
public String getExt() {
return ".jpg";
}
}