Training Resources: Glossary

LUT stands for “look-up table”; it defines how numeric pixel values are mapped to colors for display.

A LUT has configurable contrast limits that determine the pixel value range that is rendered linearly.

LUT settings must be responsibly chosen to convey the intended scientific message and not to hide relevant information.

A gray scale LUT is usually preferable over a colour LUT, especially blue and red are not well visible for many people.

For high dynamic range images multi-color LUTs may be useful to visualise a wider range of pixel values.

A watershed transform can separate touching objects if there are intensity valleys (or ridges) between touching objects. In case of intensity ridges the image needs to be inverted before being subjected to the watershed transform.

To separate object by their shape, use a distance transform on the binary image and inject this into the watershed transform. It is often good to smooth the distance transform to remove spurious minima, which could serve as wrong seed points and thus lead to an over-segmentation.