TIFF and PNG images should not be bigger than the ones created by java ImageIO

I tried to use Apache Imaging for the PDFBOX project (PDFBOX-1734) because of problems with setting the tiff resolution in java imageio.

While the code is pretty nice, I found that the generated images are sometimes much bigger in size than the ones generated by java imageio.

Example:
pdfbox-1870-devicen3-01.png 50 KB (imageio)
pdfbox-1870-devicen3.pdf-1.png 70 KB (imaging)

pdfbox-1870-devicen3-01.tif 401 KB (imageio)
pdfbox-1870-devicen3.pdf-1.tif 1063 KB (imaging)