A composition information obtaining unit calculates a mammary gland/fat ratio and a first information obtaining unit obtains imaged contrast information representing a contrast of the radiation image. A second information obtaining unit sets target application condition of X-ray, and obtains target contrast information representing an intended contrast for the radiation image based on the intended application condition. A contrast correction amount determination unit determines a contrast correction amount based on the imaged contrast information and the target contrast information. An image processing unit performs image processing, including gradation processing based on the determined contrast correction amount, on the radiation image, and obtains a processed radiation image.

A thermionic emission device includes an indirectly heatable main emitter, which is constructed as a flat emitter with a main emission surface, and at least one connectible heat emitter with a heat emission surface. The heat emission surface is disposed at a predefinable distance from the main emission surface. The main emission surface can be asymmetrically heated by the heat emission surface. In the operating state, the main emitter is at a main potential and the heat emitter is at a heating potential which differs from the main potential. An x-ray tube with the thermionic emission device has a longer service life with a consistent image quality.

A thermionic emission device includes an indirectly heatable main emitter, which is constructed as a flat emitter with a main emission surface, and at least one connectible heat emitter with a heat emission surface. The heat emission surface is disposed at a predefinable distance from the main emission surface. The main emission surface can be asymmetrically heated by the heat emission surface. In the operating state, the main emitter is at a main potential and the heat emitter is at a heating potential which differs from the main potential. An x-ray tube with the thermionic emission device has a longer service life with a consistent image quality.