Image Processing Toolbox

Using the truesize Function

The truesize function assigns a single screen pixel to each image pixel, e.g., a 200-by-300 image will be 200 screen pixels in height and 300 screen pixels in width. This is generally the preferred way to display an image. In most situations, when the toolbox is operating under default behavior, imshow calls the truesize command automatically before displaying an image.

In some cases, you may not want imshow to automatically call truesize (for example, if you are working with a small image). If you display an image without calling truesize, the image displays at the default axis size. In such cases, MATLAB must use interpolation to determine the values for screen pixels that do not directly correspond to elements in the image matrix. (See Interpolation for more information.)

You can affect whether MATLAB automatically calls truesize by using either of these methods:

• Set the preference for the current MATLAB session. This example sets the ImshowTruesize preference to 'manual', meaning that truesize will not be automatically called by imshow.

• iptsetpref('ImshowTruesize','manual')
  

• Set the preference for a single imshow command by setting the display_option parameter. This example sets the display_option parameter to truesize, so that truesize is called for the image displayed, regardless of the current preference setting.

• imshow(X, map,'truesize')
  

For more information see the reference descriptions for imshow and truesize.

Toolbox Preferences

Zooming in on a Region of an Image