# Using Nonlinear Client Coordinates

If you supply a run-time image that has a nonlinear client coordinate system, the Blob tool will operate as normal (using the pixels in the image). For each feature (blob or hole) detected in the image, the Blob tool computes the best linear approximation of the nonlinear client coordinate system at the center of mass of the feature. This local linearization is then used to map each of the feature's measurements (center of mass, area, perimeter, and so on) before returning them.

Keep in mind that any local linearization of a nonlinear client coordinate system is most accurate at the point for which the linearization is computed. In the case of a Blob feature, this point is the center of mass. Accordingly, the greatest improvement in Blob tool accuracy offered by this method is for the center of mass. Particularly in the case of larger features (those spanning more than 10 pixels), measures related to the whole feature (perimeter, area, acircularity, and the bounding box-related measures) may tend to show less improvement.