colfilt() - Image Processing

B = colfilt(A,[m n],block_type,fun) processes
the image A by rearranging each m-by-n block
of A into a column of a temporary matrix, and then
applying the function fun to this matrix. fun must
be a function handle. The function colfilt zero-pads A,
if necessary.Before calling fun, colfilt calls im2col to
create the temporary matrix. After calling fun, colfilt rearranges
the columns of the matrix back into m-by-n blocks
using col2im.block_type is a string that can have
one of the values listed in this table.Note:  


colfilt can perform operations similar to blockproc and nlfilter,
but often executes much faster.ValueDescription
'distinct'Rearranges each m-by-n distinct
block of A into a column in a temporary matrix,
and then applies the function fun to this matrix. fun must
return a matrix the same size as the temporary matrix. colfilt then
rearranges the columns of the matrix returned by fun into m-by-n distinct
blocks.
'sliding'Rearranges each m-by-n sliding
neighborhood of A into a column in a temporary
matrix, and then applies the function fun to this
matrix. fun must return a row vector containing
a single value for each column in the temporary matrix. (Column compression
functions such as sum return the appropriate type
of output.) colfilt then rearranges the vector
returned by fun into a matrix the same size as A.
B = colfilt(A,[m n],[mblock nblock],block_type,fun) processes
the matrix A as above, but in blocks of size mblock-by-nblock to
save memory. Note that using the [mblock nblock] argument
does not change the result of the operation.B = colfilt(A,'indexed',...) processes A as
an indexed image, padding with 0's if the class of A is uint8 or uint16,
or 1's if the class of A is double or single.Note  


To save memory, the colfilt function might
divide A into subimages and process one subimage
at a time. This implies that fun may be called
multiple times, and that the first argument to fun may
have a different number of columns each time.

Syntax

B = colfilt(A,[m n],block_type,fun)B = colfilt(A,[m n],[mblock nblock],block_type,fun)B = colfilt(A,'indexed',...)

Example

I = imread('tire.tif');
I2 = uint8(colfilt(I,[5 5],'sliding',@mean));
figure
subplot(1,2,1), imshow(I), title('Original Image')
subplot(1,2,2), imshow(I2), title('Filtered Image')

Output / Return Value

Limitations

Alternatives / See Also

Reference