H. Mitchell, "Practical Procedures for Breast Profiling Using Shape-from-Shading", Proc. of 3DBODY.TECH 2020 - 11th Int. Conf. and Exh. on 3D Body Scanning and Processing Technologies, Online/Virtual, 17-18 Nov. 2020, #42, https://doi.org/10.15221/20.42.
Practical Procedures for Breast Profiling Using Shape-from-Shading
Conjoint Fellow, School of Engineering, University of Newcastle, Newcastle, NSW, Australia
The measurement of female breast shapes appears to be a useful procedure for a number of medical purposes. Achieving this measurement by the numerical analysis of a single digital photograph of the breast, by utilising the principle known as shape-from-shading (SfS), is appealing because of its advantage of simplicity: the technique requires the analysis of only one image. However, the advantage of simplicity can be lost if practical implementation becomes complicated. This paper examines the practical steps required to implement the SfS measurement, in order to reflect on its feasibility.
The SfS method seeks to deduce surface gradients across an object - the breast in this case - by using the reflectance levels which are apparent in the image of the breast. From the gradients, shape can be deduced. But, because it is theoretically impossible to deduce the two parameters of surface slope from the single reflectance level at individual pixels, the method followed here is restricted to obtaining profiles which pass through the breast centre, when the theory is then simple.
Practical implementation involves a number of complications: the imagery must be taken with a flash in dark conditions, in order to provide a known illumination model; the centre of the breast should be at the centre of the image; the focal length of the camera is needed for use in the mathematical model; a means of scaling the resultant breast shape is required if a single image is used; the analysis needs to be undertaken on a monochrome image, which needs in turn to be transformed into a text file for numerical analysis; the method requires that the object has smooth physical texture and light even colouring, as the breast generally does, but the irregularly textured areola region needs to be excluded from the shape analysis; the analysis also requires finding the breast’s limits, defined as occurring when the breast rises from the background chest shape. If all these practical requirements tasks can be satisfied, the subsequent analysis is easy, involving little more than simply fitting a simple cubic or quadratic function to the reflectance levels across the breast cross-section.
Each of these practical steps is assessed in this paper, which reports on the feasibility and costs of procedures followed by the writer so far in attempts to achieve the measurement goals. It is shown that none of the problems is impossible to solve.
shape-from-shading, digital imagery, breast measurement
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