Threshold setting

Pixstat analyses pictures by classifying each pixel to either white = background or black = objects. This means that colours or grey tones have to be first separated into bright or dark pixels according to a threshold value between 1 and 255. The user can chose the threshold by selecting Threshold black/white in the Options menu. Alternatively, Pixstat can automatically calculate the optimal threshold according to an algorithm which recognises edges on the picture (Nobis & Hunziker, For. Agric. Meteorol. 128 (2005), 243-250). The determination of the threshold takes the γ (gamma) factor of the picture into account, thereby correcting for the non-linearity between real light intensity and brightness coding in the picture file. Note that the colours setting directly affects the calculation of the threshold from colour pictures.

If the threshold is set to automatic, it can be calculated by selecting Calculate threshold in the File menu or by clicking on the corresponding button . It will be calculated whenever necessary before the analysis of the pictures or before displaying a colour or grey picture in black and white.