Basic Threshold

Segmentation > Basic Threshold

Selects pixels based on whether they are below or above a certain pixel value. “Auto” determines this threshold value using Otsu’s method, which chooses the value which minimizes the average grayscale variance of the pixels which have been selected and not selected.

1. Value

Threshold value which sets pixels as selected or not

2. Select

• Dark: Selects pixels whose values are below the threshold value
• Bright: Selects pixels whose values are above the threshold value

3. Mode

• Manual: Allows manual selection of threshold value
• Auto: Auto-determines threshold value based on Otsu’s method [1]
  - Adjustment: Specifies offset to make to auto-determined threshold value.

4. Select

• Value: Selects pixels whose values are above or below the threshold value
• Percentage: Selects pixels whose values are above or below a percentage of the 0-255 image range

References

[1] Otsu, N., “A Threshold Selection Method from Gray-Level Histograms,” IEEE Transactions on Systems, Man, and Cybernetics, Vol. 9, No. 1, 1979, pp. 62-66.

Tips

• Avoid using a Basic Threshold without any pre-processing. This often results in subjective, inconsistent results.
• Recommend trying a Smart Cluster or other image normalization technique before applying a threshold.