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>  Docs Center  >  IDL Reference  >  Math - Image Processing  >  MORPH_TOPHAT

### MORPH_TOPHAT

MORPH_TOPHAT

The MORPH_TOPHAT function applies the top-hat operator to a grayscale image. The top-hat operator is implemented by first applying the opening operator to the original image, then subtracting the result from the original image. Applying the top-hat operator provides a result that shows the bright peaks within the image.

This routine is written in the IDL language. Its source code can be found in the file morph_tophat.pro in the lib subdirectory of the IDL distribution.

## Examples

The following example illustrates an application of the top-hat operator to an image in the examples/demo/demodata directory:

`; Handle TrueColor displays:DEVICE, DECOMPOSED=0; Read the imagepath=FILEPATH('pollens.jpg',SUBDIR=['examples','demo','demodata']) READ_JPEG, path, img; Create window:WINDOW, 0, XSIZE=700, YSIZE=280; Show originalXYOUTS, 180, 265, 'Original Image', ALIGNMENT=.5, /DEVICETVSCL, img, 20, 20; Radius of discr = 2; Create a binary disc of given radius.disc = SHIFT(DIST(2*r+1), r, r) LE r; Apply top-hat operatortophat = MORPH_TOPHAT(img, disc); Display stretched result.XYOUTS, 520, 265, 'Stretched Result', ALIGNMENT=.5, /DEVICETVSCL, tophat < 50, 360, 20`

## Syntax

Result = MORPH_TOPHAT ( Image, Structure [, PRESERVE_TYPE=bytearray | /UINT | /ULONG] [, VALUES=array] )

## Return Value

Returns the resulting one-, two-, or three-dimensional array.

## Arguments

### Image

A one-, two-, or three-dimensional array upon which the top-hat operation is to be performed.

### Structure

A one-, two-, or three-dimensional array to be used as the structuring element. The elements are interpreted as binary values — either zero or nonzero. The structuring element must have the same number of dimensions as the Image argument.

## Keywords

### PRESERVE_TYPE

Set this keyword to return the same type as the input array. The input array must be of type BYTE, UINT, or ULONG. This keyword only applies for grayscale erosion/dilation, and is mutually exclusive of the UINT and ULONG keywords.

### UINT

Set this keyword to return an unsigned integer array. This keyword is mutually exclusive of the ULONG and PRESERVE_TYPE keywords.

### ULONG

Set this keyword to return an unsigned longword integer array. This keyword is mutually exclusive of the UINT and PRESERVE_TYPE keywords.

### VALUES

An array of the same dimensions as the Structure argument providing the values of the structuring element. If the VALUES keyword is not present, all elements of the structuring element are 0.

## Version History

 5.3 Introduced