int numPix = (int)((1000 / pixSzMM) + 0.5);
renderParams.setPhysicalDimension(numPix, numPix, 1); // 1 means 'pix/meter'
// Encode PNG image
PNGImageEncoder encoder = new PNGImageEncoder(os, renderParams);
encoder.encode(image);
} finally {
//Only close self-created OutputStreams
if (os != firstOutputStream) {
IOUtils.closeQuietly(os);
}