用java imageio调整图片DPI，例如从96调整为300
用java imageio调整图片DPI，例如从96调整为300 - 古语云 - 博客园
Excerpt
因项目需求把图片的DPI值提升到300，否则OCR识别产生错乱：直接上源码：1、图片处理接口： 2、JEPG图片的实现类 3、PNG图片的实现类
package util.image.dpi;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.MalformedURLException;
import java.util.Iterator;
import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.metadata.IIOInvalidTreeException;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.metadata.IIOMetadataNode;
import javax.imageio.stream.ImageOutputStream;
/**
* PNG图片的实现类
* @author jffan
*
*/
public class PngDPIProcessor implements ImageDPIProcessor {
/**
* 1英寸是2.54里面
*/
private static final double INCH_2_CM = 2``.54d;
/**
* 根据文件后缀扩展名判断是否能进行处理
* @param fileName
* @return
*/
@Override
public boolean canHandle(String fileName) {
assert fileName != null : "fileName should not be null"``;
return fileName.endsWith(``"png"``) || fileName.endsWith(``"PNG"``);
}
/**
* 处理图片，设置图片DPI值
* @param path
* @param dpi dot per inch
* @return
* @throws IOException
*/
@Override
public byte``[] process(BufferedImage image, int dpi) throws MalformedURLException, IOException {
for (Iterator<ImageWriter> iw = ImageIO.getImageWritersByFormatName(``"png"``); iw.hasNext();) {
ImageWriter writer = iw.next();
ImageWriteParam writeParam = writer.getDefaultWriteParam();
ImageTypeSpecifier typeSpecifier = ImageTypeSpecifier.createFromBufferedImageType(BufferedImage.TYPE_INT_RGB);
IIOMetadata metadata = writer.getDefaultImageMetadata(typeSpecifier, writeParam);
if (metadata.isReadOnly() || !metadata.isStandardMetadataFormatSupported()) {
continue``;
}
ByteArrayOutputStream output = new ByteArrayOutputStream();
ImageOutputStream stream = null``;
try {
setDPI(metadata, dpi);
stream = ImageIO.createImageOutputStream(output);
writer.setOutput(stream);
writer.write(metadata, new IIOImage(image, null``, metadata), writeParam);
} finally {
try {
stream.close();
} catch (IOException e) {
}
}
return output.toByteArray();
}
return null``;
}
/**
* 设置图片的DPI值
* @param metadata
* @param dpi
* @throws IIOInvalidTreeException
* @author 范继峰
* @date 2019年7月30日上午10:53:18
* @return void
*/
private void setDPI(IIOMetadata metadata, int dpi) throws IIOInvalidTreeException {
double dotsPerMilli = 1.0 * dpi / 10 / INCH_2_CM;
IIOMetadataNode horiz = new IIOMetadataNode(``"HorizontalPixelSize"``);
horiz.setAttribute(``"value"``, Double.toString(dotsPerMilli));
IIOMetadataNode vert = new IIOMetadataNode(``"VerticalPixelSize"``);
vert.setAttribute(``"value"``, Double.toString(dotsPerMilli));
IIOMetadataNode dim = new IIOMetadataNode(``"Dimension"``);
dim.appendChild(horiz);
dim.appendChild(vert);
IIOMetadataNode root = new IIOMetadataNode(``"javax_imageio_1.0"``);
root.appendChild(dim);
metadata.mergeTree(``"javax_imageio_1.0"``, root);
}
}