By performing a reduction of the spatial resolution over a total of two times by the low-frequency characteristic generator 43 and the low-frequency image generation unit 41, the radiation image processing apparatus of this invention reduces the amount of calculation by reducing the influence of noise. Also, among the feature quantity extracted through feature extraction unit 42 and the low-frequency image generation unit 41, reduced by reduction of the spatial resolution of the low-frequency feature generation unit 43, an extra characteristic amount that can not be removed (pattern) it becomes possible. Therefore, as regards the irradiation field region extracted and low frequency characteristics that were generated by the low-frequency feature generation unit 43, the region extraction unit 44 of the subsequent stage, to reduce the influence of noise or the like, to reduce the amount of computation. As a result, it is possible to realize the region extraction and feature extraction high accuracy by reducing the influence of noise or the like, to reduce the amount of computation.この発明の放射線画像処理装置は、低周波画像生成部41および低周波特徴生成部43による合計2回にわたる空間分解能の低下を行って、ノイズ等の影響を減らして演算量を低減させる。また、低周波画像生成部41および特徴抽出部42を経て抽出された特徴量のうち、除去しきれなかった余分な特徴量(パターン)を、低周波特徴生成部43の空間分解能の低下によって減らすことが可能となる。したがって、低周波特徴生成部43により生成された低周波特徴や、後段の領域抽出部44により抽出された照視野領域について、ノイズ等の影響を減らし、演算量を低減させることができる。その結果、ノイズ等の影響を減らして精度の高い特徴抽出および領域抽出を実現し、演算量を低減させることができる。
