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The Threshold algorithm replaces the image pixel values with the fill values specified by a user. The pixel values change or remain unchanged depending on whether the original color value is within the threshold range. For RGB or RGBa images, the Threshold command works on each individual RGB channel.

Image types

You can apply this algorithm to all 2D, 3D, and 4D color (RGB) and grayscale images.

Applying the Threshold algorithm

To use this algorithm, do the following:

  1. Select Algorithms > Segmentation> Threshold in the MIPAV window. The Threshold dialog box (Figure 1) appears.
  2. Complete the information in the dialog box.
  3. Click OK. The algorithm begins to run, and a progress bar appears momentarily with the status. When the algorithm finishes running, the progress bar disappears, and the results appear in a separate image window.

Dialog box options:

Figure 1. The Threshold dialog box.


Apply same threshold to all channels
If checked, applies the same threshold values to all RGB channels. In that case only the Red box becomes available for entering the threshold values. Other boxes became unavailable.
Use <red, green, or blue> channel
Applies the threshold operation to each channel independently. For each pixel, the R, G, and B values will set to 255 if it is in range for that particular channel and to 0 otherwise.
Use inverse threshold
If checked, changes all pixels which are outside of the specified range. In that case you must specify the desired pixel values into the Set outside values text box.
Red, Green, Blue
For each channel, specify the threshold values in the corresponding boxes - Red, Green or Blue:
Lower limit - end of threshold range;
Upper Limit - beginning of threshold range;
Set outside values to: enter the pixel values for pixels outside the threshold.
New image - places the result of the algorithm in a new image window.
Replace image - replaces the current active image with the results of the algorithm.
Whole image - applies the algorithm to the whole image.
VOI region(s)- applies the algorithm to the selected VOI(s).
OK - applies the algorithm according to the specifications in this dialog box.
Cancel- disregards any changes that you made in the dialog box and closes this dialog box.
Help -Displays online help for this dialog box.