Java: BufferedImage to byte array and back

Question

I see that a number of people have had a similar problem, however I'm yet to try find exactly what I'm looking for.

So, I have a method which reads an input image and converts it to a byte array:

    File imgPath = new File(ImageName);
    BufferedImage bufferedImage = ImageIO.read(imgPath);
    WritableRaster raster = bufferedImage .getRaster();
    DataBufferByte data   = (DataBufferByte) raster.getDataBuffer();

What I now want to do is convert it back into a BufferedImage (I have an application for which I need this functionality). Note that "test" is the byte array.

    BufferedImage img = ImageIO.read(new ByteArrayInputStream(test));
    File outputfile = new File("src/image.jpg");
    ImageIO.write(img,"jpg",outputfile);

However, this returns the following exception:

    Exception in thread "main" java.lang.IllegalArgumentException: im == null!

This is because the BufferedImage img is null. I think this has something to do with the fact that in my original conversion from BufferedImage to byte array, information is changed/lost so that the data can no longer be recognised as a jpg.

Does anyone have any suggestions on how to solve this? Would be greatly appreciated.

Answer 1

This is recommended to convert to a byte array

ByteArrayOutputStream baos = new ByteArrayOutputStream(); ImageIO.write(img, "jpg", baos); byte[] bytes = baos.toByteArray(); 

Answer 2

Note that calling close or flush will do nothing, you can see this for yourself by looking at their source/doc:

Closing a ByteArrayOutputStream has no effect.

The flush method of OutputStream does nothing.

Thus use something like this:

ByteArrayOutputStream baos = new ByteArrayOutputStream(THINK_ABOUT_SIZE_HINT);
boolean foundWriter = ImageIO.write(bufferedImage, "jpg", baos);
assert foundWriter; // Not sure about this... with jpg it may work but other formats ?
byte[] bytes = baos.toByteArray();

Here are a few links concerning the size hint:

• Java: Memory efficient ByteArrayOutputStream
• jpg bits per pixel

Of course always read the source code and docs of the version you are using, do not rely blindly on SO answers.