I've also started to use the xBR filter for some MS-DOS titles (i.e. Explosiv, Northern Lights, Morning Star, etc.). The current xBR filter compatible with DOSBox doesn't smooth gradients as the HQx filter will, so it's primarily used to smoothly scale up line art images, producing smooth lines for a wider variety of angles than HQx. A recent xBR update appears to smooth gradients, but it is currently only compatible with emulators supporting multi-pass shaders.