To satisfy fast image zooming requirement with preserving edge-sharpness, a quasi-bilinear algorithm based on profile curvature of brightness surface is introduced. Firstly, in view of inherent low-pass property of bilinear, an amendatory formula is established via including pixel variation. Then, for obtaining the dominant direction of neighboring pixels, image coordinate and its brightness are treated as surface when gray value being simulated as altitude of earth surface. Lastly, magnitudes of curvatures of specified direction is regarded as adjustment reference of structures type of image, such as edge or texture. Therefore, weights of direction of a pair of two pixels average can be adaptively evaluated according to several thresholds of curvatures. Experiment results of synthetic data demonstrate that, compared with other similar techniques, Power Signal to Noise Ratio (PSNR) gain of image twice-interpolated is 7.8 dB, and improvement of Structural Similarity (SSIM) is 0.1. Especially, arithmetic type of proposed algorithm is simple, and its complexity is relatively low, thus it is convenient to real-time application over fixed platform.