1. An image display apparatus comprising: input means for entering image data; quantizing means for quantizing the entered image data by quantizing input data while correcting an error between input data and output data; and display means for displaying an image based upon the quantized data from said quantizing means, with said display means displaying the image by scanning a specific area by non-interlacing and scanning other areas by interlacing, wherein said quantizing means performs quantization, starting while correcting the error from the entered image data for a preceding area located a plurality of lines before the specific area without storing error data of the preceding area in a memory, when said display means scans the specific area by the non-interlacing, and wherein said quantizing means outputs the quantized data in the specific area without outputting the quantized data in the preceding area.