A method and apparatus is provided to generate two X-ray projection images, using different focal-spot sizes in the X-ray source. The large and small focal-spot images have different image qualities (e.g., different signal-to-noise rations (SNR) and different resolution). The two images are combined, in either the spatial or frequency domains, to generate a combined image, exhibiting the best attributes of the constitutive small and large focal-spot images. In the spatial domain, change regions and uniform regions are determined based on spatial variations within the images, and the superposition generating the combined image weights the small focal-spot image more in the change regions and the large focal-spot image more in the uniform regions. In the frequency domain, the combined image superimposes low-frequency components of the large focal-spot image with high-frequency components of the small focal-spot image.
