1. An image processing apparatus comprising: an outline extracting section for extracting an outline pixel composing an outline area of an image; a first screen processing section for performing a multi-level screen processing to image data of the image; a second screen processing section for performing a bi-level screen processing to estimate a screen dot output condition for a peripheral pixel of the outline pixel, wherein the screen dot output condition specifies whether or not a screen dot is outputted for the peripheral pixel; and an outline processing section for determining whether to output or not to output a dot with respect to the outline pixel extracted by the outline extracting section and subjected to the multi-level screen processing by the first screen processing section, based on the screen dot output condition estimated by the second screen processing section for the peripheral pixel of the outline pixel.