Point operations

A step used to process an image in some way can be called an operation.

The simplest operations are point operations, which act on individual pixels. Point operations change each pixel in a way that depends upon its own value, but not upon where it is in the image nor upon the values of other pixels. This is in contrast to neighborhood operations, which calculate new pixel values based upon the values of pixels nearby.

While not immediately very glamorous, point operations often have indispensable roles in more interesting contexts – and so it’s essential to know how they are used, and what complications to look out for.

Isn’t modifying pixels bad?

Part I stressed repeatedly that modifying pixels is a bad thing. Since image processing is all about changing pixel values, it’s time to add a bit more nuance:

Modifying pixel values is bad – unless you have a good reason.

A ‘good reason’ is something you can justify based upon the image data. Something you could confidently include in a journal article describing how you analyzed your image, and convince a reviewer was sensible.

You should also make sure to apply the processing to a duplicate of the image, and keep the original file. That way you can always return to the original data if you need to.