object detection is an important task in computer vision and machine intelligence systems. multistage particle windows (mpw), proposed by gualdi et al., is an algorithm of fast and accurate object detection. by sampling particle windows (pws) from a proposal distribution (pd), mpw avoids exhaustively scanning the image. despite its success, it is unknown how to determine the number of stages and the number of pws in each stage. moreover, it has to generate too many pws in the initialization step and it unnecessarily regenerates too many pws around object-like regions. in this paper, we attempt to solve the problems of mpw. an important fact we used is that there is a large probability for a randomly generated pw not to contain the object because the object is a sparse event relative to the huge number of candidate windows. therefore, we design a pd so as to efficiently reject the huge number of nonobject windows. specifically, we propose the concepts of rejection, acceptance, and ambiguity windows and regions. then, the concepts are used to form and update a dented uniform distribution and a dented gaussian distribution. this contrasts to mpw which utilizes only on region of support. the pd of mpw is acceptance-oriented whereas the pd of our method (called ipw) is rejection-oriented. experimental results on human and face detection demonstrate the efficiency and the effectiveness of the ipw algorithm. the source code is publicly accessible.