From: https://ww2.mathworks.cn/help/images/ref/bwareaopen.html
Remove small objects from binary image
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BW2 = bwareaopen(BW,P)
BW2 = bwareaopen(BW,P,conn)
example
removes all connected components (objects) that have fewer than BW2
= bwareaopen(BW
,P
)P
pixels from the binary image BW
, producing another binary image, BW2
. This operation is known as an area opening.
BW2 = bwareaopen(
removes all connected components, where BW
,P
,conn
)conn
specifies the desired connectivity.
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Try This Example
Read binary image.
BW = imread('text.png');
Remove objects containing fewer than 50 pixels using bwareaopen
function.
BW2 = bwareaopen(BW, 50);
Display original image next to morphologically opened image.
imshowpair(BW,BW2,'montage')
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BW
— Binary imageBinary image, specified as a nonsparse, logical or numeric array of any dimension.
Example: BW2 = bwareaopen(BW, 50);
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| logical
P
— Maximum number of pixels in objectsMaximum number of pixels in objects, specified as a nonnegative, integer-valued, numeric scalar.
Example: BW2 = bwareaopen(BW, 50);
Data Types: double
conn
— Pixel connectivity4
| 8
| 6
| 18
| 26
| 3-by-3-by- ... -by-3 matrix of 0
s and 1
sPixel connectivity, specified as one of the values in this table. The default connectivity is 8
for 2-D images, and 26
for 3-D images.
Value |
Meaning |
|
---|---|---|
Two-Dimensional Connectivities |
||
4-connected |
Pixels are connected if their edges touch. Two adjoining pixels are part of the same object if they are both on and are connected along the horizontal or vertical direction. |
|
8-connected |
Pixels are connected if their edges or corners touch. Two adjoining pixels are part of the same object if they are both on and are connected along the horizontal, vertical, or diagonal direction. |
|
Three-Dimensional Connectivities |
||
6-connected |
Pixels are connected if their faces touch. Two adjoining pixels are part of the same object if they are both on and are connected in:
|
|
18-connected |
Pixels are connected if their faces or edges touch. Two adjoining pixels are part of the same object if they are both on and are connected in
|
|
26-connected |
Pixels are connected if their faces, edges, or corners touch. Two adjoining pixels are part of the same object if they are both on and are connected in
|
For higher dimensions, bwareaopen
uses the default value
.conndef
(ndims(BW),'maximal')
Connectivity can also be defined in a more general way for any dimension by specifying a 3-by-3-by- ... -by-3 matrix of 0
s and 1
s. The 1
-valued elements define neighborhood locations relative to the center element of conn
. Note that conn
must be symmetric about its center element. See Specifying Custom Connectivities for more information.
Data Types: double
| logical
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BW2
— Image that has been morphologically openedImage that has been morphologically opened, specified as a nonsparse, logical array the same size as BW
.
The basic steps are
Determine the connected components:
CC = bwconncomp(BW, conn);
Compute the area of each component:
S = regionprops(CC, 'Area');
Remove small objects:
L = labelmatrix(CC);
BW2 = ismember(L, find([S.Area] >= P));