Band math

Perform calculations, per pixel or object, using arithmetic and logical expressions of spectral band values.

Parameters

Expression

The expression to evaluate using the syntax w[WAVE_LENGHT] or b[INDEX] to specify bands. If the wavelength syntax is used, the band with the closest wavelength value will be selected. This also applies if the wavelength is outside of the data cube.

Range operator :, standard arithmetic (+,-,/,* …) and comparison operators (=,>,< …) as well as some mathematical expressions (…) and constant values () can be used in expressions.

Note that Breeze does not validate the provided expression until you click Apply changes to apply it to some data.

Expand to see all available operators

Arithmetic Operator	Description
`-`	Subtract
`+`	Add
`/`	Divide
`*`	Multiply
`%`	Modulo
`^`	Raised to a power

Generic Operator	Description
`:`	Range operator, average a range of values. For example: `w1200:w1500` yields average value of all data points between wavelength 1200 nm and 1500 nm.

Comparison Operator	Description
`=`	Equal to
`\|` `OR`	TRUE if any of the conditions separated by OR is TRUE
`&` `AND`	TRUE if all the conditions separated by AND is TRUE
`!=` `<>`	Not equal to
`<`	Less than
`<=`	Less than or equal to
`>`	Greater than
`>=`	Greater than or equal to

Function operator	Description
`SQRT(N)`
`SIN(N)`
`COS(N)`
`EXP(N)`
`LOG(N)`
`LOG10(N)`
`AVG(N)`
`ROUND(N)`

Constants	Description
`TRUE`	Always evaluates to TRUE
`FALSE`	Always evaluates to FALSE
`INF`	token value
`PI`	approximated to

To average over a spectral region, the following expression is used “:”, see example 2 below.

Type

If the expression should be applied to pixels in an image or entire objects

Object
- Average spectrum for each object
Pixels
- Values for each pixel in the object

Min

The minimum value used in the visualization of the object in the Table, corresponding to the darkest blue color seen in the Legend. Values lower values than Min will also be displayed with the same color.

This limit can also be specified and auto-adjusted by right-clicking in the Legend in Table.

Max

The maximum value used in the visualization of the object in the Table, corresponding to the darkest red color seen in the Legend. Values higher than Max will also be displayed with the same color.

This limit can also be specified and auto-adjusted by right-clicking in the Legend in Table.

Smooth

Smooth prediction result using median filter kernel

None
- No Smoothing prediction.
Low
- Smoothing using median filter kernel with 5x5 pixel box
Medium
- Smoothing using median filter kernel with 10x10 pixel box
High
- Smoothing using median filter kernel with 15x15 pixel box

Examples

Example 1

In this example, we aim to investigate whether the ratio between two wavelengths is larger than that of another wavelength for the object average spectrum. In expression, we write the following

(w1700 / w2200) > w1200

This will returns 1 if the ratio of intensity between bands at 1700 nm and 2200 nm is larger than the value of intensity at 1200 nm.

For type, we choose 'object' to focus only on the segmented object average.

The min and max are left at 0 and 1, respectively

The parameters for the descriptor should look like this

Example 2

In this example, we investigate the ratio between two wavelength averages on the pixel level.

The expression we will use is

(w2335:w2345)/(w1445:w1455)

For Type, we leave it at 'pixels'.

Min is left at 0, but max is changed to 2.

The parameters in the software should look like this