Displaying Binary Images :: Displaying and Exploring Images (Image Processing Toolbox User's Guide)

Image Processing Toolbox User's Guide

Displaying Binary Images

In MATLAB, a binary image is of class logical. Binary images contain only 0's and 1's. Pixels with the value 0 are displayed as black; pixels with the value 1 are displayed as white.

Note For the toolbox to interpret the image as binary, it must be of class logical. Grayscale images that happen to contain only 0's and 1's are not binary images.

To display a binary image, using either imshow or imtool, specify the image matrix as an argument. For example, this code reads a binary image into the MATLAB workspace and then displays the image. This documentation uses the variable name BW to represent a binary image in the workspace

```
BW = imread('circles.png');
imshow(BW)
```

```
imtool(BW)
```

Changing the Display Colors of a Binary Image

You might prefer to invert binary images when you display them, so that 0 values are displayed as white and 1 values are displayed as black. To do this, use the NOT (~) operator in MATLAB. (In this figure, a box is drawn around the image to show the image boundary.) For example:

```
imshow(~BW)
```

```
imtool(~BW)
```

You can also display a binary image using the indexed image colormap syntax. For example, the following command specifies a two-row colormap that displays 0's as red and 1's as blue.

```
imshow(BW,[1 0 0; 0 0 1])
```

```
imtool(BW,[1 0 0; 0 0 1])
```

Displaying Grayscale Images Displaying Truecolor Images