使用 ImageIO.write() 创建一个 JPEG 创建一个 0 字节的文件

Question

I am trying to write a method that takes an image, and saves a 100 by 100 thumbnail of that image. However, when I save the file, it comes out as an unreadable 0 byte image (with the error "Error interpreting JPEG image file (Improper call to JPEG library in state 200)") in Ubuntu's ImageViewer. My code is as follows:

public boolean scale(){

    String file = filename.substring(filename.lastIndexOf(File.separator)+1);
    File out = new File("data"+File.separator+"thumbnails"+File.separator+file);

    if( out.exists() ) return false;

    BufferedImage bi;
    try{
        bi = ImageIO.read(new File(filename));
    }
    catch(IOException e){
        return false;
    }

    Dimension imgSize = new Dimension(bi.getWidth(), bi.getHeight());
    Dimension bounds = new Dimension(100, 100);
    int newHeight = imgSize.height;
    int newWidth = imgSize.width;

    if( imgSize.width > bounds.width ){
        newWidth = bounds.width;
        newHeight = (newWidth*imgSize.height)/imgSize.width;
    }

    if( imgSize.height > bounds.width ){
        newHeight = bounds.height;
        newWidth = (newHeight*imgSize.width)/imgSize.height;
    }

    Image img = bi.getScaledInstance(newWidth, newHeight, BufferedImage.SCALE_SMOOTH);
    BufferedImage thumb = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_4BYTE_ABGR);
    Graphics2D g2d = thumb.createGraphics();
    g2d.drawImage(img, 0, 0, null);
    g2d.dispose();

    try{
        ImageIO.write(thumb, "jpg", out);
    }
    catch(IOException e){
        return false;
    }

    return true;
}

Where "filename" is a global variable for the class housing this method, representing the path to the original image. My main issue is that I do not see why I'm creating a 0 byte image.

Answer 1

So, the issue was this. I'm working in OpenJDK. OpenJDK doesn't have a JPEG encoder, apparently, so while the file was being created by

ImageIO.write(thumb, "jpg", out);

it wasn't actually creating anything for the file to save; hence the empty 0 byte unreadable file. Changing the ImageIO argument to "png" (and adjusting the new File() extension, appropriately) successfully created the desired image with the above code.

Answer 2

I experienced the same issue even though the JVM had a JPG encoder and it was caused by using an unsupported type of BufferImage underneath. I had used BufferedImage.TYPE_USHORT_GRAY which is evidently not supported and gave no error messages but produced a 0 byte file. When I switched to BufferedImage.TYPE_BYTE_GRAY it worked perfectly.

Answer 3

JPG have no alpha channel, ImageIO.write() will fail silently (just return false) one way is to copy your image into another one

BufferedImage newBufferedImage = new BufferedImage(bufferedImage.getWidth(),
  bufferedImage.getHeight(), BufferedImage.TYPE_INT_RGB);
newBufferedImage.getGraphics().drawImage(bufferedImage, 0, 0, null);

boolean write = ImageIO.write(newBufferedImage, extension, outputfile);
if (!write) {
  // do something
}