磁盘上的映像文件大小（KB）随着java中动态映像大小调整（缩小大小）而增加

I'm new to Java. I resized the large sized png files to standard file size by maintaining the aspect ratio. Below is the code snippet that i used. But the downside i see in this code snippet is that, after re-size the file size is much larger than the original. For e.g original is 5kb and the re-sized new one is 16kb.I'm new to Java. I resized the large sized png