blkproc (Image Processing Toolbox)

Implement distinct block processing for an image

Syntax

B = blkproc(A,[m n],fun)
B = blkproc(A,[m n],fun,P1,P2,...)
B = blkproc(A,[m n],[mborder nborder],fun,...)
B = blkproc(A,'indexed',...)

Description

B = blkproc(A,[m n],fun) processes the image A by applying the function fun to each distinct m-by-n block of A, padding A with zeros if necessary. fun is a function that accepts an m-by-n matrix, x, and returns a matrix, vector, or scalar y.

```
y = fun(x)
```

blkproc does not require that y be the same size as x. However, B is the same size as A only if y is the same size as x.

B = blkproc(A,[m n],fun,P1,P2,...) passes the additional parameters P1,P2,..., to fun.

B = blkproc(A,[m n],[mborder nborder],fun,...) defines an overlapping border around the blocks. blkproc extends the original m-by-n blocks by mborder on the top and bottom, and nborder on the left and right, resulting in blocks of size (m+2*mborder)-by-(n+2*nborder). The blkproc function pads the border with zeros, if necessary, on the edges of A. The function fun should operate on the extended block.

The line below processes an image matrix as 4-by-6 blocks, each having a row border of 2 and a column border of 3. Because each 4-by-6 block has this 2-by-3 border, fun actually operates on blocks of size 8-by-12.

```
B = blkproc(A,[4 6],[2 3],fun,...)
```

B = blkproc(A,'indexed',...) processes A as an indexed image, padding with zeros if the class of A is uint8 or uint16, or ones if the class of A is double.

Class Support

The input image A can be of any class supported by fun. The class of B depends on the class of the output from fun.

Example

fun can be a function_handle created using @. This example uses blkproc to compute the 2-D DCT of each 8-by-8 block to the standard deviation of the elements in that block.

I = imread('cameraman.tif');
fun = @dct2;
J = blkproc(I,[8 8],fun);
imagesc(J), colormap(hot)

fun can also be an inline object. This example uses blkproc to set the pixels in each 8-by-8 block to the standard deviation of the elements in that block.

I = imread('alumgrns.tif');
fun = inline('std2(s)*ones(size(x))');
I2 = blkproc(I,[8 8],'std2(x)*ones(size(x))');
imshow(I)
figure, imshow(I2,[]);

See Also

colfilt, nlfilter, inline

bestblk brighten