I believe these are the lines you need to look at. In this file --> dosbox-SVN.conf Found here --> /opt/retropie/configs/pc fullresolution= aspect= scaler= Use your monitor's native resolution for the first option. Use aspect=true, if you want the correct aspect ratio - after scaling. False, if you want it stretched to fill your monitor. scaler=XXXX - XXXX=your scaler of choice...none, normal2x, normal3x, advmame2x,....etc... Use this to scale the image.