**Name**

**llremove** Remove small level lines in an gray level image

**Command Synopsis**

**llremove** [-i] [-l *Lmin*] [-L *Lmax*] *input* *output*

-i : Invert: remove first gray levels local minima and then local maxima

-lLmin: Minimal level lines length (local gray levels minima)

-LLmax: Minimal level lines length (local gray levels maxima)

input: Original fimage

output: Output fimage with missing level lines

**Function Summary**

Fimage llremove (Input , Lmin , Lmax , invert )

Fimage Input ;

int *Lmin , *Lmax ;

char *invert ;

**Description**

This module applies a morphological thresholding of extrema gray levels values
in small areas.
The critical size of the area in given by the minimal length of the level lines
to keep (in pixels).
This length threshold (10 by default) can be changed using the options
`-l`

and `-L`

.
The option `-l`

is related to the minima gray levels while the option
`-L`

is for the maxima.

You don't get the same result if you begin by removing the gray levels maxima
and then the gray levels minima (the default) or if you remove first the
gray levels minima, and after the the gray levels maxima.
Select the option `-i`

if you want this second order.
This order of thresholding is important since, by removing a level
line (and therefore a level set), close but non-connex level sets of same
value can be made connex so that the length of the new level line is upper
the threshold, and the new level line will not be removed.

Therefore, the gray levels average of the output image obtained by this
module called without the option `-i`

is always less than the
one obtained with the option `-i`

.

You may get some applications of this filter in [Fro00]
and [Fro99].
It is a good example of a very simple use of the modules `ml_decompose`

and
`ml_reconstruct`

. However, since the Fast Level Sets
Transform [MG00] (`flst`

) has been implemented,
you would get faster computation by using flst-based modules
(such as `fgrain`

, which considers the area instead of the length).

**See Also**

`ll_remove`, `ml_decompose`, `ml_reconstruct`.

**Version 1.1**

Last Modification date : Thu Jan 24 18:42:10 2002

**Author**

Jacques Froment