After some horsing around here is what appears to work, but my choice
of type  TYPE_INT_BGR was arbitrary.  It seems goofy to change from
JPEG to bit map to convert back to JPEG map gain.

// magnify which has side effect of turning back to plain Image.
Image magnifiedImage
 = image.getScaledInstance( magnifiedImageWidth,
                                         magnifiedImageHeight,
                                         BufferedImage.SCALE_SMOOTH);

// convert back to BufferedImage
BufferedImage bufferedImage = new BufferedImage (

magnifiedImageWidth,

magnifiedImageHeight,

BufferedImage.TYPE_INT_BGR);
bufferedImage.createGraphics().drawImage(
                       magnifiedImage, 0, 0, this /* observer */ );

// write out the BufferedImage as a JPEG
ImageIO.write( bufferedImage,
                       "JPEG" /* format desired */ ,
                        file );

.