Documentation |
Apply 2-D spatial transformation to image
imtransform is not recommended. Use imwarp instead.
B = imtransform(A,tform)
B = imtransform(A,tform,interp)
[B,xdata,ydata] = imtransform(...)
[B,xdata,ydata] = imtransform(...,Name,Value)
B = imtransform(A,tform) transforms the image A according to the 2-D spatial transformation defined by tform. If ndims(A) > 2, such as for an RGB image, then imtransform applies the same 2-D transformation to all 2-D planes along the higher dimensions.
B = imtransform(A,tform,interp) specifies the form of interpolation to use.
[B,xdata,ydata] = imtransform(...) returns the location of the output image B in the output X-Y space. By default, imtransform calculates xdata and ydata automatically so that B contains the entire transformed image A. However, you can override this automatic calculation by specifying values for the 'XData' and 'YData' arguments.
[B,xdata,ydata] = imtransform(...,Name,Value) transforms the image with additional options for controlling various aspects of the spatial transformation specified by one or more Name,Value pair arguments.
A |
An image of any nonsparse numeric class (real or complex) or of class logical. |
tform |
A spatial transformation structure returned by maketform or cp2tform. imtransform assumes spatial-coordinate conventions for the transformation tform. Specifically, the first dimension of the transformation is the horizontal or x-coordinate, and the second dimension is the vertical or y-coordinate. This convention is the reverse of the array subscripting convention in MATLAB^{®}. |
interp |
A string that specifies the form of interpolation to use. interp can be one of the following strings: 'bicubic', 'bilinear', or 'nearest' (nearest-neighbor). Alternatively, interp can be a resampler structure returned by makeresampler. This option allows more control over how imtransform performs resampling. Default: 'bilinear' |
Optional comma-separated pairs of Name,Value arguments, where Name is the argument name and Value is the corresponding value. Name must appear within single quotes (' ') and is not case sensitive. You can specify several name and value pair arguments in any order as Name1, Value1, ..., NameN, ValueN.
'UData' |
A two-element, real vector that, when combined with 'VData', specifies the spatial location of image A in the 2-D input space U-V. The two elements of 'UData' give the u-coordinates (horizontal) of the first and last columns of A, respectively. Default: [1 size(A,2)] | ||||||||||||||
'VData' |
A two-element, real vector that, when combined with 'UData', specifies the spatial location of image A in the 2-D input space U-V. The two elements of 'VData' give the v-coordinates (vertical) of the first and last rows of A, respectively. Default: [1 size(A,1)] | ||||||||||||||
'XData' |
A two-element, real vector that, when combined with 'YData', specifies the spatial location of the output image B in the 2-D output space X-Y. The two elements of 'XData' give the x-coordinates (horizontal) of the first and last columns of B, respectively. Default: If you do not specify 'XData' and 'YData', imtransform estimates values that contain the entire transformed output image. To determine these values, imtransform uses the findbounds function. | ||||||||||||||
'YData' |
A two-element real vector that, when combined with 'XData', specifies the spatial location of the output image B in the 2-D output space X-Y. The two elements of 'YData' give the y-coordinates (vertical) of the first and last rows of B, respectively. Default: If you do not specify 'XData' and 'YData', imtransform estimates values that contain the entire transformed output image. To determine these values, imtransform uses the findbounds function. | ||||||||||||||
'XYScale' |
A one- or two-element real vector. The first element of 'XYScale' specifies the width of each output pixel in X-Y space. The second element (if present) specifies the height of each output pixel. If 'XYScale' has only one element, then the same value specifies both width and height. Default: If you do not specify 'XYScale' but you do specify 'Size', then imtransform calculates 'XYScale' from 'Size', 'XData', and 'YData'. If you do not provide 'XYScale' or 'Size', then imtransform uses the scale of the input pixels for 'XYScale', except in cases where an excessively large output image would result.
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'Size' |
A two-element vector of nonnegative integers that specifies the number of rows and columns of the output image B. For higher dimensions, imtransform takes the size of B directly from the size of A. Thus, size(B,k) equals size(A,k) for k > 2. Default: If you do not specify 'Size', imtransform derives this value from 'XData', 'YData', and 'XYScale'. | ||||||||||||||
'FillValues' |
An array containing one or several fill values. The imtransform function uses fill values for output pixels when the corresponding transformed location in the input image is completely outside the input image boundaries. If A is 2-D, 'FillValues' requires a scalar. However, if A's dimension is greater than two, then you can specify 'FillValues' as an array whose size satisfies the following constraint: size(fill_values,k) must equal either size(A,k+2) or 1. For example, if A is a uint8 RGB image that is 200-by-200-by-3, then possibilities for 'FillValues' include the following values.
If A is 4-D with size 200-by-200-by-3-by-10, then you can specify 'FillValues' as a scalar, 1-by-10, 3-by-1, or 3-by-10. |
Simple Transformation. Apply a horizontal shear to an intensity image:
I = imread('cameraman.tif'); tform = maketform('affine',[1 0 0; .5 1 0; 0 0 1]); J = imtransform(I,tform); imshow(I), figure, imshow(J)
Horizontal Shear
Projective Transformation. Map a square to a quadrilateral with a projective transformation:
% Set up an input coordinate system so that the input image % fills the unit square with vertices (0 0),(1 0),(1 1),(0 1). I = imread('cameraman.tif'); udata = [0 1]; vdata = [0 1]; % Transform to a quadrilateral with vertices (-4 2),(-8 3), % (-3 -5),(6 3). tform = maketform('projective',[ 0 0; 1 0; 1 1; 0 1],... [-4 2; -8 -3; -3 -5; 6 3]); % Fill with gray and use bicubic interpolation. % Make the output size the same as the input size. [B,xdata,ydata] = imtransform(I, tform, 'bicubic', ... 'udata', udata,... 'vdata', vdata,... 'size', size(I),... 'fill', 128); subplot(1,2,1), imshow(I,'XData',udata,'YData',vdata), ... axis on subplot(1,2,2), imshow(B,'XData',xdata,'YData',ydata), ... axis on
Projective Transformation
Image Registration. Register an aerial photo to an orthophoto.
Read an aerial photo into the MATLAB workspace and view it.
unregistered = imread('westconcordaerial.png'); figure, imshow(unregistered)
Aerial Photo
Read an orthophoto into the MATLAB workspace and view it.
figure, imshow('westconcordorthophoto.png')
Orthophoto
Load control points that were previously picked.
load westconcordpoints
Create a transformation structure for a projective transformation using the points.
t_concord = cp2tform(movingPoints,fixedPoints,'projective');
Get the width and height of the orthophoto, perform the transformation, and view the result.
info = imfinfo('westconcordorthophoto.png'); registered = imtransform(unregistered,t_concord,... 'XData',[1 info.Width], 'YData',[1 info.Height]); figure, imshow(registered)
Transformed Image
checkerboard | cp2tform | imresize | imrotate | makeresampler | maketform | tformarray