1. A method of grading tubules, which may be any of round, oval, cylindrical or irregularly shaped, in a first image of a histological specimen, the method comprising using computer apparatus to carry out the steps of: a) providing a second image distinguishing first objects in the first image which are sufficiently large to indicate potential tubules and have pixel values at boundaries indicating epithelial layers, the first objects being processed so as to fill in any holes therein, by setting pixel values within the hole to its boundary value, b) providing a third image distinguishing second objects in the first image which have pixel values not indicating epithelial layers but instead fat and holes within said potential tubules, c) combining data from the second and third images to identify as holes within tubules those second objects which are contained within first objects by excluding objects not indicated to have epithelial layers and first objects not containing second objects, said second objects being contained second objects, d) performing one or more of the following: i) counting as tubules those of the first objects which have contained second objects within them to provide a number of tubules parameter, ii) counting the first objects to provide a number of objects parameter and determining a parameter expressing the number of tubules parameter as a proportion of the number of objects parameter, iii) determining the relative areas of the contained second objects as proportions of respective first objects within which they are located to provide respective ratio parameters, iv) determining the total area of contained second objects as a proportion of total area of first objects within which they are located to provide a surface area ratio parameter, and v) counting the number of first objects containing second objects having a ratio parameter as calculated in step iii) of at least 0.03, to provide a tubules parameter, e) grading the first image's tubules on the basis of the one or more parameters as aforesaid with reference to parameter threshold values, and f) using the grading of the first image's tubules to provide a tubule score for use in diagnosis.