Segmentation > Adaptive Threshold

Selects pixels as either black or white based on their intensity relative to some statistic of the surrounding neighborhood.

In the common Percentage mode, with “Statistic” set to Box Mean, pixel values are compared to their local average grayscale value. For example, if Percentage and Box Mean modes are checked, “White Pixels” is set to Above, Percentage value is 98, and Window Size is 30, then a pixel has to be more than 98% of the average grayscale value in a 30×30 pixel window centered around it, in order to be set to white. If “White Pixels” is set to Below, then the pixel must be less than 98% of its local 30×30 window average to be set to white.

The window size is typically best set to be just larger than the size of the largest feature one is hoping to capture. The Distance Line tool can help approximate this size.

1. White Pixels

  • Above: White pixels will be those that meet or exceed the criteria
  • Below: White pixels will be those that meet or fall below the criteria
  • Both: White pixels will be those that are the more than critical departure value above or bellow their neighborhood statistic. Only applies to “Departure” mode.

2. Statistic

  • Box Mean: Critical stat for each pixel is the mean of its neighborhood
  • Box Median: Critical stat for each pixel is the median of its neighborhood
  • Gaussian Mean: Critical stat for each pixel is the Gaussian mean of its neighborhood

3. Dynamic

  • On: Critical difference or percentage for each pixel will be scaled based on local variance
    - Direct: Higher local variance will raise critical difference or percentage
    - Inverse: Higher local variance will lower critical difference or percentage
  • Weight: Sets how strong the local variance will scale the critical difference or percentage

4. Mask

Only considers and thresholds pixels within the black features of the mask image

5. Operation

  • Departure: Sets the critical threshold for each pixel as its difference from its neighborhood statistic
  • Percentage: Sets the critical threshold for each pixel as its difference from its neighborhood statistic

6. Percentage/Departure Value

Sets the critical value each pixel get assessed relative to (Recommended: Percentage = 100)

7. Window Size

Size of the local neighborhood that each pixel is considered against (Recommended: 30)

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