Image Processing Toolbox

imtophat

Perform top-hat filtering

Syntax

• IM2 = imtophat(IM,SE)
  IM2 = imtophat(IM,NHOOD)
  

Description

IM2 = imtophat(IM,SE) performs morphological top-hat filtering on the grayscale or binary input image IM using the structuring element SE, where SE is returned by strel. SE must be a single structuring element object, not an array containing multiple structuring element objects.

IM2 = imtophat(IM,NHOOD), where NHOOD is an array of 0's and 1's that specifies the size and shape of the structuring element, is the same as imptophat(IM,strel(NHOOD)).

Class Support

IM can be numeric or logical and must be nonsparse. The output image, IM2, has the same class as the input image. If the input is binary (logical), then the structuring element must be flat.

Example

You can use top-hat filtering to correct uneven illumination when the background is dark. This example uses top-hat filtering with a disk-shaped structuring element to remove the uneven background illumination from the image rice.tif.

1. Read the image into the MATLAB workspace.

• I = imread('rice.tif');
  imshow(I), title('Original')
  
  
  

2. Create the structuring element and perform top-hat filtering of the image.

• se = strel('disk',12);
  J = imtophat(I,se);
  figure, imshow(J), title('Step 1: Top-hat filtering')
  
  
  

3. Use imadjust and stretchlim to make the result more easily visible.

• K = imadjust(J,stretchlim(J));
  figure, imshow(K), title('Step 2: Contrast adjustment')
  
  
  

See Also

imbothat, strel

imsubtract

imtransform