有关 java 设置图片 DPI
作者：夜的第七章
- 2023-11-09 山西
本文字数：1976 字
阅读完需：约 6 分钟
背景：
java 端调用 python 算法修图接口后，返回了 base64 字符串，需要将 base64 字符串转图片，用文件流的方式写入图片会增大图片大小，不太明白当中为什么会增大，代码如下：
String base64String = "base64字符串";BASE64Decoder decode = new BASE64Decoder();byte[] imageBytes = decode.decodeBuffer(base64String);FileOutputStream stream = new FileOutputStream("test.jpg");stream.write(imageBytes);stream.close();
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而用 ImageIO.wirte 来写入图片，不会增大图片大小，但输出的图片 dpi 会变为 96,可能是默认会设置为 96dpi,手动设置一下图片 dpi,代码如下：
public void base642img() { //读取txt文件为String String base64String = FileUtils.readFileToString(new File("D:\\tmp\\A0001\\1.1.1\\A0001-1.1.1-0004\\result\\test.txt"), "utf-8"); BASE64Decoder decode = new BASE64Decoder(); byte[] imageBytes = decode.decodeBuffer(base64String); ByteArrayInputStream inputStream = new ByteArrayInputStream(imageBytes); BufferedImage image = ImageIO.read(inputStream); JpegDPIProcessor processor = new JpegDPIProcessor(); byte[] img = processor.process(image,300); //将img字节写到本地 try (FileOutputStream outputStream = new FileOutputStream("D:\\tmp\\A0001\\1.1.1\\A0001-1.1.1-0004\\result\\test.jpg");){ outputStream.write(img); }}复制代码
import lombok.SneakyThrows;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;import java.awt.image.BufferedImage;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.util.Iterator;
public class JpegDPIProcessor { private String formatName = "jpeg"; public byte[] process(BufferedImage image, int dpi) throws IOException { for (Iterator<ImageWriter> iw = ImageIO.getImageWritersByFormatName(formatName); iw.hasNext();) { ImageWriter writer = iw.next(); ImageWriteParam writeParams = writer.getDefaultWriteParam(); ImageTypeSpecifier typeSpecifier = ImageTypeSpecifier.createFromBufferedImageType(BufferedImage.TYPE_INT_RGB); IIOMetadata metadata = writer.getDefaultImageMetadata(typeSpecifier, writeParams); if (metadata.isReadOnly() || !metadata.isStandardMetadataFormatSupported()) { continue; } String metadataFormat = "javax_imageio_jpeg_image_1.0"; IIOMetadataNode root = new IIOMetadataNode(metadataFormat); IIOMetadataNode jpegVariety = new IIOMetadataNode("JPEGvariety"); IIOMetadataNode markerSequence = new IIOMetadataNode("markerSequence"); IIOMetadataNode app0JFIF = new IIOMetadataNode("app0JFIF"); app0JFIF.setAttribute("majorVersion", "1"); app0JFIF.setAttribute("minorVersion", "2"); app0JFIF.setAttribute("thumbWidth", "0"); app0JFIF.setAttribute("thumbHeight", "0"); app0JFIF.setAttribute("resUnits", "01"); app0JFIF.setAttribute("Xdensity", String.valueOf(dpi)); app0JFIF.setAttribute("Ydensity", String.valueOf(dpi)); root.appendChild(jpegVariety); root.appendChild(markerSequence); jpegVariety.appendChild(app0JFIF); metadata.mergeTree(metadataFormat, root); ByteArrayOutputStream out = new ByteArrayOutputStream(); ImageOutputStream stream = null; try { stream = ImageIO.createImageOutputStream(out); writer.setOutput(stream); writer.write(metadata, new IIOImage(image, null, metadata), writeParams); } finally { stream.close(); } return out.toByteArray(); } return null; }}复制代码
使用 Java 原生的 jdk 即可实现设置图片 dpi
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