An apparatus and method for enlarging a source image on a computer display is described. A scanline buffer stores pixels in a first row of the source image. Coordination circuitry receives from a processor and stores pixels in a second row of the source image. Blend circuitry generates output pixels, such that each of the output pixels corresponds to a weighted average of a plurality of input pixels. The plurality of input pixels comprises two pixels stored in the scanline buffer and two pixels stored in the coordination circuitry. Control circuitry determines weight values and provides the weight values to the blend circuitry for calculating the weighted average. The control circuitry also determines, based on the weight values, which pixels stored in the scanline buffer and in the coordination circuitry are used by the blend circuitry as the input pixels. In addition, the control circuitry replaces the pixels in the scanline buffer with corresponding pixels from the coordination circuitry after the last time the pixels in the scanline buffer are used as the input pixels.