The Threshold Function

The Threshold function (Colors > Threshold) converts a color or grayscale image into a pure black-and-white graphic. More specifically, it represents areas with a brightness value of less than 50% black and a brightness value of more or equal to 50% white.

If the Preview control is checked, you will see a pure black-and-white representation in the image window. The Threshold Range input boxes allow you to manually select the upper and lower intensity ranges, i.e., the black-white distribution in the image. You can either enter numerical values in the intended fields or you can move the sliders beneath the histogram curve with the left mouse button.

The Linear and Logarithmic buttons in the upper-right corner can be clicked to determine how the histogram will be represented in the visual graph.