An apparatus and method for deinterlacing video images with improved slope detection is described. In one exemplary implementation, the apparatus includes an input buffer, a processor, and an output buffer. The input buffer is configured to receive a video stream in an interlaced format. The processor is configured to convert the video stream from the interlaced format to a progressive format. This conversion process includes calculating the slope for a diagonal line of an image at a pixel to-be-interpolated (i.e., at a missing pixel) using a slope protection operation to increase the accuracy of the slope calculation. The output buffer is then configured to transmit the video stream in the progressive format.