The present invention relates to an image processing device, an information storage device, an image processing method, and the like.
When observing tissue using an endoscope apparatus, and making a diagnosis, a method has been widely used that determines whether or not an early lesion has occurred by observing the surface of tissue as to the presence or absence of minute irregularities (irregular parts). When using an industrial endoscope apparatus instead of a medical endoscope apparatus, it is useful to observe the object (i.e., the surface of the object in a narrow sense) as to the presence or absence of an irregular structure in order to detect whether or not a crack has occurred in the inner side of a pipe that is difficult to directly observe with the naked eye, for example. It is normally useful to detect the presence or absence of an irregular structure from the processing target image (object) when using an image processing device other than an endoscope apparatus.
A process that enhances a specific spatial frequency has been widely used as a process for enhancing a structure (e.g., an irregular structure such as a groove) within the captured image. However, this method is not suitable for detecting the presence or absence of minute irregularities (see above). A method has also been known that effects some change in the object, and captures the object, instead of detecting the presence or absence of irregularities by image processing. For example, when using a medical endoscope apparatus, the contrast of the mucous membrane in the surface area may be increased by spraying a dye (e.g., indigocarmine) to stain the tissue. However, it takes time and cost to spray a dye, and the original color of the object, or the visibility of a structure other than irregularities, may be impaired due to the sprayed dye. Moreover, the method that sprays a dye to tissue may be highly invasive for the patient.
JP-A-2003-88498 discloses a method that enhances an irregular structure by comparing the luminance level of an attention pixel in a locally extracted area with the luminance level of its peripheral pixel, and coloring the attention area when the attention area is darker than the peripheral area.
The process disclosed in JP-A-2003-88498 is designed based on the assumption that the object (i.e., the surface of tissue) is captured darkly when the distance from the imaging section to the object is long, since the intensity of reflected light from the surface of the tissue decreases.