Compress image without saving it -- in Java

Question

Is there a way, in Java, to compute what the size of a compressed image will be w/o saving the image? (This will be used to determine the quality necessary to compress an image to a specific size.)

Something like this, but in Java instead of C#, and where the Stream can be a dead end.

Java's `MemoryStream` equivalent is `ByteArrayOutputStream`. Once you compress the image you can [write it to that stream](https://docs.oracle.com/javase/7/docs/api/javax/imageio/ImageIO.html#write(java.awt.image.RenderedImage,%20java.lang.String,%20java.io.OutputStream)), get the size in bytes and discard the stream. — BackSlash, Jul 03 '19 at 12:49
@BackSlash: I fear the answer is to write my own, but is there a stream I could use that wouldn't even save the data in memory but still allow me to determine what the size *would* have been? — Scott Hunter, Jul 03 '19 at 12:53
@ScottHunter AFAIK no default way. But you could extend InputStream and instead of storing the bytes just count the length. Should be painless — Matthew Kerian, Jul 03 '19 at 12:59

score 2 · Accepted Answer · answered Jul 03 '19 at 13:25

Here's a simple implementation.

public class LengthCounterOutputStream extends OutputStream{

    private int byteCounter = 0;

    @Override
    public void write(int b){
        byteCounter++;
    }

    @Override
    public void write(@NotNull byte[] b){
        this.write(b, 0, b.length);
    }

    @Override
    public void write(@NotNull byte[] b, int off, int len){
        byteCounter += len;
    }

    public int getByteCounter(){
        return byteCounter;
    }
}

Compress image without saving it -- in Java

1 Answers1

Linked