Optimized thumbnail generation
You probably reached the maximum speed you can achieve with the API you are using. You could try the following extra hints, just in case they’re not the default values:

g2dBuffer.setRenderingHint(RenderingHints.KEY_RENDERING,
                                              RenderingHints.VALUE_RENDER_SPEED);
g2dBuffer.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
                                              RenderingHints.VALUE_ANTIALIAS_OFF);
g2dBuffer.setRenderingHint(RenderingHints.KEY_DITHERING, 
                                              RenderingHints.VALUE_DITHER_DISABLE);
g2dBuffer.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, 
                                              RenderingHints.VALUE_COLOR_RENDER_SPEED);


Also, try replacing TYPE_INT_RGB with TYPE_INT_BGR or TYPE_3BYTE_BGR to experiment with how efficiently the Java graphics libraries do their byte packing. But it’s pretty unlikely you’ll see a noticeable difference.