如何將grails中的png/gif/jpg轉換爲jpg以保持圖像中的高質量？

Question

我使用以下方法將圖像轉換爲jpg。我的解決方案的問題是，它會降低質量。

什麼是保持圖像質量，同時減小文件大小的好方法？

def convertToJpg(currentImage) { 
    try { 
     InputStream inStreamCrop = new ByteArrayInputStream(currentImage) 
     BufferedImage bufferedImage = ImageIO.read(inStreamCrop) 

     // create a blank, RGB, same width and height, and a white background 
     BufferedImage newBufferedImage = new BufferedImage(bufferedImage.getWidth(), 
       bufferedImage.getHeight(), BufferedImage.TYPE_INT_RGB); 
     newBufferedImage.createGraphics().drawImage(bufferedImage, 0, 0, Color.WHITE, null); 

     ByteArrayOutputStream baos=new ByteArrayOutputStream() 
     // write to jpeg file 
     ImageIO.write(newBufferedImage, "jpg", baos); 
     baos.flush() 
     def image = baos.toByteArray() 
     baos.close() 
     return image 

    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

Answer 1

您可以通過獲取ImageWriter對象並通過參數設置來控制JPEG的質量。例如：

import javax.imageio.stream.* 
import javax.imageio.* 

BufferedImage bufferedImage = ImageIO.read(new File("test.png")); 
float quality = 0.9; 
ImageWriter writer = ImageIO.getImageWritersByFormatName("jpg").next(); 
ImageWriteParam param = writer.getDefaultWriteParam(); 
param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); 
param.setCompressionQuality(quality); 
writer.setOutput(new FileImageOutputStream(new File("test.jpg"))); 
writer.write(null, new IIOImage(bufferedImage, null, null), param); 

質量參數的範圍介於0和1之間，其中1的壓縮率最低。嘗試不同的值;我發現0.9是低壓縮（但大文件大小）的好選擇。

注意JPEG圖像不與OpenJDK的支持：ImageIO not able to write a JPEG file