PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of stably performing a gradation processing of a pectoral X-ray image without depending on a lung field detecting technique, and an X-ray image diagnostic apparatus.SOLUTION: A vertebra distribution region 52 including a vertebra region in which the vertebra of a body to be examined is photographed, is set based on a pixel value or at least one of the pixel position in the pectoral X-ray image to the pectoral X-ray image obtained by photographing the pectoral part of the body to be examined, and the vertebra distribution region 52 is divided into a plurality of small regions 53a, 53b, 53c... standing in a line along the body axial direction of the pectoral part X-ray image. Then, on respective small regions 53a, 53b, 53c..., first profiles 54a, 54b, 54c...showing the distribution of characteristic quantities of the pixel values of the pixel rows standing in a line along the body axial direction are formed, and the pixels corresponding to the pixel values being at most a first threshold value determined based on the minimum value in the first profile, are extracted from respective small regions as a vertebra region 56. The characteristic quantity of the pixel value of the extracted vertebra region 56 is calculated, and the gradation processing is performed so that the characteristic quantity becomes a target value.COPYRIGHT: (C)2012,JPO&INPIT【課題】肺野検出手法に依存することなく、胸部X線画像の階調処理を安定して行うことができる画像処理装置及びX線画像診断装置を提供する。【解決手段】被検体の胸部を撮影して得た胸部X線画像に対し、画素値又は前記胸部X線画像における画素位置の少なくとも一つに基づいて、被検体の椎体が撮影された椎体領域を含む椎体分布領域52を設定し、その椎体分布領域52を胸部X線画像の体軸方向に沿って並んだ複数の小領域53a、53b、53c・・・に分割する。そして、小領域53a、53b、53c・・・毎に、体軸方向に沿って並んだ画素列の画素値の特徴量の分布を示す第1プロファイル54a、54b、54c・・・を生成し、当該第1プロファイルにおける最小値を基に定めた第1閾値以下の画素値に相当する画素を、各小領域から椎体領域56として抽出する。抽出された椎体領域56の画素値の特徴量を算出し、その特徴量が目標値となるように階調処理を行う。【選択図】図7
