Particle Analysis - Intensity Selection

The fundamental property that is used to select image pixels is the intensity (brightness) value. The brightness you wish to select is determined by an expression that you type into the Particle Analysis frame. An example is shown below.

In this simple example, the expression GE 100 has been entered. Here, GE stands for "greater than or equal to" 100. All the intensity selectors are shown below:

Intensity selector Description

GE Greater than or equal to.

GT Greater than.

LE Less than or equal to.

LT Less than.

Intensity selector	Description
GE	Greater than or equal to.
GT	Greater than.
LE	Less than or equal to.
LT	Less than.

In addition, boolean operators can be applied to refine the intensity range. These are:

Boolean operator Description

&& Logical AND.

|| Logical OR.

&! Logical AND NOT

|! Logical OR NOT.

Boolean operator	Description
&&	Logical AND.
\|\|	Logical OR.
&!	Logical AND NOT
\|!	Logical OR NOT.

Using the intensity selectors, and boolean operators, pixels within any range (or ranges) of intensity can be isolated within the image. Some example intensity expressions are shown below:

Example Expression Description

GE 100 Selects only pixels whose intensities are greater than or equal to 100.

GT 0 && LT 100 Selects only pixels whose intensities are greater than 0 and less than 100 (1-99 inclusive).

LT 100 || GT 200 Excludes pixels whose intensities are between 100 and 200 inclusive. (i.e., selects pixels with intensities that are either less than 100 or greater than 200).

(GT 100 &! GT 200) || (GT 300 &! GT 500) Selects pixels with intensity ranges 101-200 and 301-500 inclusive.

Example Expression	Description
GE 100	Selects only pixels whose intensities are greater than or equal to 100.
GT 0 && LT 100	Selects only pixels whose intensities are greater than 0 and less than 100 (1-99 inclusive).
LT 100 \|\| GT 200	Excludes pixels whose intensities are between 100 and 200 inclusive. (i.e., selects pixels with intensities that are either less than 100 or greater than 200).
(GT 100 &! GT 200) \|\| (GT 300 &! GT 500)	Selects pixels with intensity ranges 101-200 and 301-500 inclusive.

The formal BNF for an intensity-selection expression is given below. To remind you of the correct form of an intensity expression, some example expressions are given in the menu to the right of the intensity expression pane.

Backus-Naur Form of an Intensity Expression

`<intensity-expression> ::=`	`<simple-intensity-spec> \| <compound-intensity-spec>`
`<simple-intensity-spec> ::=`	`<relational-operator value> \| <(relational-operator value)>`
`<compound-intensity-spec> ::=`	`<intensity-expression boolean-operator intensity-expression> \| <(intensity-expression boolean-operator intensity-expression)>`
`<relational-operator> ::=`	`GE \| LE \| GT \| LT`
`<boolean-operator> ::=`	`‘\|\|’ \| ‘&&’ \| ‘\|&’ ‘\|!’`

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