An image processing method and a display device are provided. The display device includes a computation circuit and a display panel. In the image processing method, at first, an original image including a straight line pattern and upper pixels is provided. The straight line pattern includes lower pixels opposite to the upper pixels. The display panel includes first lower sub-pixel structures corresponding to the first lower pixels and first upper sub-pixel structures corresponding to the first upper pixels. Thereafter, vertical sub-pixel rendering methods are performed on pixel luminances of the first lower pixels and the upper first upper pixels to obtain rendering sub-pixel luminances of the first lower pixels and the upper first upper pixels. Then, the first lower sub-pixel structures and the first upper sub-pixel structures are driven according to the rendering sub-pixel luminances.