Methods and apparatus for interpolating existing gray-level pixel data to obtain new pixel values during image reduction and enlargement. A quadratic interpolation equation is used to apply location weighting factors to the density values of neighboring pixels. Edge strength modifying factors are used to modify the weighting factors in the x, y, and diagonal directions. In one embodiment, the modifying factors are set to greater than unity when the corresponding edge strength is greater than a predetermined threshold value. In another embodiment, the modifying factors are a non-linear function of the edge strength. These techniques preserve the sharpness of high contrast edges in the original image.