Speckle reduction method

A projection apparatus comprising a light source for projecting an illumination light through an illumination optical system to a spatial light modulator (SLM) for modulating the illumination light for generating and transmitting an image projection light to an image projection surface through a projection optical system to display an image. The projection apparatus further includes an image process unit for receiving and analyzing an input image data; and the image process unit applies a conversion process to a signal related to the input image data to generate different control patterns for a plurality of adjacent pixel elements included in the SLM for a predetermined period during at least one frame period to reproduce a gradation of the pixel whereby each of the plurality of adjacent pixel elements has a gradation of approximately a same level.