Chances are that raw pixel values are not the most informative way to represent the data, as we have already realized in Chapter 3, Finding Objects via Feature Matching and Perspective Transforms. Instead, we need to derive a measurable property of the data that is more informative for classification.
However, often, it is not clear which features would perform best. Instead, it is often necessary to experiment with different features that the practitioner finds appropriate. After all, the choice of features might strongly depend on the specific dataset to be analyzed or the specific classification task to be performed.
For example, if you have to distinguish between a stop sign and a warning sign, then the most distinctive feature might be the shape of the sign or the color scheme. However, if you have to distinguish between two warning...
