Class: Gradient Amplification

 

The Gradient Amplification module is a new class for sliceOmatic 5.0.  This class enable you to artificially increase the gradient around a specific target GLI value.  This will help segmentation techniques that are gradient based (such as "Morpho" and "Snake"). It can be used for example in segmenting CT images where you know you want to segment at specific Hounsfield values but do not want to use threshold based techniques.  By increasing the gradient at the desired Hounsfield value, you insure that the gradient based technique will find the correct boundary.

 

The Gradient Amplification class is enabled through the 2D Mode: "DB Class management" interface.  Once you have an instance of this class in your database tree, a new "Gradient" button will be present in the Modes menu.  This button will open the gradient amplification's interface.

 

 

 

 

 

As an example we have an image composed of a linearly decreasing values of GLI (from 255 to 0) starting from a point in the center of the image.

 

Since there is no clear gradient variation in this image, the "Morpho" mode will be enable to compute a good watershed of the image.

 

By increasing the gradient of the image at GLI=100, we create an artificial drop in the GLI values around GLI=100, and enable "Morpho" to latch to the desired value.

Original Images

Watershed

Modified Image

"Morpho" segmentation

 

 

 

You can create multiple instances of the class and use these to create multiples false gradients (here at GLI=100, 150 and 200).

 

Instancing the class 3 times

Modified Image

"Morpho" segmentation

 

Note:

 

If you use multiple instances of the class, there must be no overlap in the affected GLI values.

 

 

From the Graphic Interface

 

 

 

Instance selection

 

Select which of the instances of the class you want to work on.

GLI Graph

 

This graph show you the modifications that will be applied to the GLI value.  The horizontal axis represent the original GLI values while the vertical axis represent the modified values.

Center Value

 

The class affect a small range of the GLI values.  This parameter is used to select the center of the affected region.

Power

Specify the shape of the transformation curve.  The values range from 1.0 (no changes) to 0.0 (sharp changes)

 

Power = 1.0

Power = 0.5

Power = 0.0

 

Affected Range

 

The class affect a small range of the GLI values.  This parameter is used to select the width of the affected region.

Update DB

Clicking on this button will apply this filter to the selected images.

 

 

The GLI Computation

 

Using the notation:

 

X

= old GLI value

 

X'

= new GLI value

 

C

= Center

 

W

= Affected Range

 

P

= Power

 

∆

= (C - X) = Distance from Center

 

Depending on the value of ∆, there are 4 possibilities when computing the new GLI value X':

 

 

∆ < -W

 

X' = X (We are outside the affected range)

 

(∆ < 0) And (∆ > -W)

 

X' = X - (∆/W)P * W

 

(∆ > 0) And (∆ < W)

 

X' = X + (∆/W)P * W

 

∆ > W

 

X' = X (We are outside the affected range)

 

 

From the Display Area

 

There is no Display Area interaction specific to this class.

 

 

From the Keyboard

 

There is no keyboard interface specific to this class.

 

 

From the Command Line

 

There is no command line or variables directly associated with this class.