从图像格式8BPP创建BufferedImage

Question

In my project I receive an Base64-encoded image that is in a greyscale 8BPP format. I am having trouble converting this into a BufferedImage. I have some code that works when I read an image (f.ex png) from disk, base64-encode it and the reverse the process.

Anyway, when I try to convert my received String, everything seems to work, but null is returned. It is not the catch that is invoked, but rather ImageIO.read that returns null.

Any suggestions? I know that the base64 string is valid, because I have tried to save it as a raw file and open it in an editor, which shows the image properly.

This is my code:

public static BufferedImage convertBase64StringToBufferedImage(String base64String){
    byte[] pictureBytes = Base64Coder.decode(base64String);

    InputStream is = new ByteArrayInputStream(pictureBytes);

    BufferedImage image;
    try {
        image = ImageIO.read(new ByteArrayInputStream(pictureBytes));
    } catch (IOException e) {
        log.error(e.getMessage(), e);
        return null;
    }
    return image;
}

Answer 1

From the documentation :

Returns a BufferedImage as the result of decoding a supplied InputStream with an ImageReader chosen automatically from among those currently registered. The InputStream is wrapped in an ImageInputStream. If no registered ImageReader claims to be able to read the resulting stream, null is returned.

Here's the code that gets executed:

public static BufferedImage read(ImageInputStream stream)
    throws IOException {
    if (stream == null) {
        throw new IllegalArgumentException("stream == null!");
    }

    Iterator iter = getImageReaders(stream);
    if (!iter.hasNext()) {
        return null;                  // <~~~~~ here's your null
    }

    ImageReader reader = (ImageReader)iter.next();
    ImageReadParam param = reader.getDefaultReadParam();
    reader.setInput(stream, true, true);
    BufferedImage bi;
    try {
        bi = reader.read(0, param);
    } finally {
        reader.dispose();
        stream.close();
    }
    return bi;
}

Perhaps you can try explicitly getting an ImageReader based on the appropriate mime-type, and do the read code (as seen above) with that reader.