图片无法放大?

使用ScaleParameter对图片进行缩放,缩小是正常的..但是无法放大.请问下是什么原因

WriteParameter wp = new WriteParameter();
wp.setDefaultQuality(level);
ScaleParameter sp = new ScaleParameter(width, height, ScaleParameter.Algorithm.LANCZOS);
ImageRender ir = new ReadRender(bis, true);
ImageRender sc = new ScaleRender(ir, sp);
wr = new WriteRender(sc, bos, ImageFormat.getImageFormat(FilenameUtils.getExtension(outFile.getName())), wp);
wr.render();

Start by reproducing the reported enlargement behavior with the shown ScaleParameter, ReadRender, ScaleRender, and WriteRender sequence, comparing it with the working reduction case. Trace how the requested width and height move through ScaleParameter and ScaleRender, and consider the issue done when enlargement either works with the expected output format or the limitation is documented with a clear explanation.

Written by the indexing model from the issue text.