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imref2d

Reference 2-D image to world coordinates

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Description

An imref2d object stores the relationship between the intrinsic coordinates anchored to the rows and columns of a 2-D image and the spatial location of the same row and column locations in a world coordinate system.

The image is sampled regularly in the planar world-x and world-y coordinate system such that intrinsic-x values align with world-x values, and intrinsic-y values align with world-y values. The resolution in each dimension can be different.

Creation

You can create an imref2d object in these ways.

  • affineOutputView — Store the spatial extent of an image that is warped by a 2-D affine geometric transformation.

  • The imref2d function described here

Syntax

R = imref2d
R = imref2d(imageSize)
R = imref2d(imageSize,pixelExtentInWorldX,pixelExtentInWorldY)
R = imref2d(imageSize,xWorldLimits,yWorldLimits)

Description

R = imref2d creates an imref2d object with default property settings.

R = imref2d(imageSize) sets the optional ImageSize property.

R = imref2d(imageSize,pixelExtentInWorldX,pixelExtentInWorldY) sets the optional ImageSize, PixelExtentInWorldX, and PixelExtentInWorldY properties.

example

R = imref2d(imageSize,xWorldLimits,yWorldLimits) sets the optional ImageSize, XWorldLimits, and YWorldLimits properties.

example

Properties

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Span of image in the x-dimension in the world coordinate system, specified as a numeric scalar. The imref2d object sets this value as PixelExtentInX * ImageSize(2).

Data Types: double

Span of image in the y-dimension in the world coordinate system, specified as a numeric scalar. The imref2d object sets this value as PixelExtentInY * ImageSize(1).

Data Types: double

Number of elements in each spatial dimension, specified as a 2-element positive row vector. ImageSize is the same form as that returned by the size function.

Data Types: double

Size of a single pixel in the x-dimension measured in the world coordinate system, specified as a positive number.

Data Types: double

Size of a single pixel in the y-dimension measured in the world coordinate system, specified as a positive number.

Data Types: double

Limits of image in world x-dimension, specified as a 2-element row numeric vector [xMin xMax].

Data Types: double

Limits of image in world y-dimension, specified as a 2-element numeric row vector [yMin yMax].

Data Types: double

Limits of image in intrinsic units in the x-dimension, specified as a 2-element row vector [xMin xMax]. For an m-by-n image (or an m-by-n-by-p image), XIntrinsicLimits equals [0.5, n+0.5].

Data Types: double

Limits of image in intrinsic units in the y-dimension, specified as a 2-element row vector [yMin yMax]. For an m-by-n image (or an m-by-n-by-p image), YIntrinsicLimits equals [0.5, m+0.5].

Data Types: double

Object Functions

containsDetermine if image contains points in world coordinate system
intrinsicToWorldConvert from intrinsic to world coordinates
sizesMatchDetermine if object and image are size-compatible
worldToIntrinsicConvert from world to intrinsic coordinates
worldToSubscriptConvert world coordinates to row and column subscripts

Examples

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Open Live Script

Read a 2-D grayscale image into the workspace.

A = imread('pout.tif');

Create an imref2d object, specifying the size and world limits of the image associated with the object.

xWorldLimits = [2 5];
yWorldLimits = [3 6];
RA = imref2d(size(A),xWorldLimits,yWorldLimits)
RA = 
  imref2d with properties:

           XWorldLimits: [2 5]
           YWorldLimits: [3 6]
              ImageSize: [291 240]
    PixelExtentInWorldX: 0.0125
    PixelExtentInWorldY: 0.0103
    ImageExtentInWorldX: 3
    ImageExtentInWorldY: 3
       XIntrinsicLimits: [0.5000 240.5000]
       YIntrinsicLimits: [0.5000 291.5000]

Display the image, specifying the spatial referencing object. The axes coordinates reflect the world coordinates.

figure
imshow(A,RA);

Figure contains an axes object. The axes object contains an object of type image.

Open Live Script

Read a 2-D grayscale image into the workspace.

m = dicominfo('knee1.dcm');
A = dicomread(m);

Create an imref2d object, specifying the size and the resolution of the pixels. The DICOM file contains a metadata field PixelSpacing that specifies the image resolution in each dimension in millimeters per pixel.

RA = imref2d(size(A),m.PixelSpacing(2),m.PixelSpacing(1))
RA = 
  imref2d with properties:

           XWorldLimits: [0.1562 160.1562]
           YWorldLimits: [0.1562 160.1562]
              ImageSize: [512 512]
    PixelExtentInWorldX: 0.3125
    PixelExtentInWorldY: 0.3125
    ImageExtentInWorldX: 160
    ImageExtentInWorldY: 160
       XIntrinsicLimits: [0.5000 512.5000]
       YIntrinsicLimits: [0.5000 512.5000]

Display the image, specifying the spatial referencing object. The axes coordinates reflect the world coordinates.

figure
imshow(A,RA,'DisplayRange',[0 512])

Figure contains an axes object. The axes object contains an object of type image.

Compare the width of the image in world coordinates and intrinsic coordinates. This image width in intrinsic coordinates, with units of pixels, is:

RA.ImageSize(1)
ans = 
512

The image width in world coordinates, with units of millimeters, is:

RA.ImageExtentInWorldX
ans = 
160

More About

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Tips

  • You can create an imref2d object for an RGB image. If you create the object specifying the ImageSize property as a three-element vector (such as that returned by the size function), only the first two elements are used to set ImageSize.

Extended Capabilities

Version History

Introduced in R2013a

See Also

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