1. A medical image processing apparatus, comprising: a display; and processing circuitry configured, by executing a program, to extract at least part of a lung from three-dimensional image data, extract a tubular structure from at least part of the extracted lung, calculate area ratios between a lumen and a wall of the extracted tubular structure along the tubular structure, and generate area ratio images by allocating pixel values, corresponding to the calculated area ratios, to corresponding positions on the tubular structure having the area ratios being calculated, and displays the area ratio images on the display.