Documentation

images.geotrans.Warper

Apply same geometric transformation to many images efficiently

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Description

AWarperobject creates an image warper from anaffine2dorprojective2dgeometric transformation object for images with a specific size.

Creation

Syntax

w = images.geotrans.Warper(tform,inputSize)
w = images.geotrans.Warper(tform,inputRef)
w = images.geotrans.Warper(tform,inputRef,outputRef)
w = images.geotrans.Warper(sourceX,sourceY)
w = images.geotrans.Warper(___,Name,Value)

Description

example

w = images.geotrans.Warper(tform,inputSize)creates an image warper from the geometric transformation objecttformfor images with sizeinputSize.

w = images.geotrans.Warper(tform,inputRef)creates an image warper, whereinputRefspecifies the coordinate system of the input images.

w = images.geotrans.Warper(tform,inputRef,outputRef)creates an image warper, whereoutputRefspecifies the coordinate system of the output image. This syntax can be used to improve performance by limiting the application of the geometric transformation to a specific output region of interest.

w = images.geotrans.Warper(sourceX,sourceY)creates an image warper, wheresourceXandsourceYspecify the input image coordinates required to perform the geometric transformation.sourceXandsourceYare 2-D matrices of the same size as the required output image. Each (x,y) index insourceXandsourceYspecifies the location in the input image for the corresponding output pixel.

w = images.geotrans.Warper(___,Name,Value)sets properties using one or more name-value pairs, for any of the previous syntaxes. For example,warper = images.geotrans.Warper(tform,size(im),'FillValue',1)specifies the value used for pixels outside the original image. Enclose each property name in single quotes.

Input Arguments

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Geometric transformation, specified as anaffine2dorprojective2dgeometric transformation object.

Input image size, specified as a 1-by-2 or 1-by-3 vector of the form[m n]or[m n p].

Data Types:single|double|int8|int16|int32|uint8|uint16|uint32

Referencing object associated with the input image, specified as animref2dspatial referencing object.

Referencing object associated with the output image, specified as animref2dspatial referencing object.

Input image coordinates, specified as a 2-D matrix the same size as the required output image.

Data Types:single

Properties

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Size of the input images, specified as a two-element vector of the form[m n]or a three-element vector of the form[m n p].

Data Types:single|double|int8|int16|int32|int64|uint8|uint16|uint32|uint64|logical

Size of the first two dimensions of the output image, specified as a two-element vector of the form[m n].

Data Types:single|double|int8|int16|int32|int64|uint8|uint16|uint32|uint64|logical

Interpolation method, specified as'linear','nearest', or'cubic'.

Data Types:char|string

Value used for output pixels outside the input image boundaries, specified as a numeric scalar.Warpercasts the fill value to the data type of the input image.

Data Types:single|double|int8|int16|int32|int64|uint8|uint16|uint32|uint64

Object Functions

warp Apply geometric transformation

例子

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Open Live Script

Pick a set of images of the same size. The example uses a set of images that show cells.

imds = imageDatastore(fullfile(matlabroot,'toolbox','images','imdata','AT*'));

创建一个geometric transform to rotate each image by 45 degrees and to shrink each image.

tform = affine2d([ 0.5*cos(pi/4) sin(pi/4) 0; -sin(pi/4) 0.5*cos(pi/4) 0; 0 0 1]);

创建一个Warperobject, specifying the geometric transformation object,tform, and the size of the input images.

im = readimage(imds,1); warper = images.geotrans.Warper(tform,size(im));

Determine the number of images to be processed and preallocate the output array.

numFiles = numel(imds.Files); imr = zeros([warper.OutputSize 1 numFiles],'like',im);

Apply the geometric transformation to each of the input images by calling thewarpfunction of theWarperobject.

forind = 1:numFiles im = read(imds); imr(:,:,1,ind) = warp(warper,im);end

Visualize the output images. (Turn off the warning message about the images being scaled for display.)

warning('off','images:initSize:adjustingMag') montage(imr);

Tips

  • If the input images havepplanes ([m,n,p]),warpapplies the transform to each plane independently.

Algorithms

Warperis optimized to apply the same geometric transformation across a batch of same size images.Warperachieves this optimization by splitting the warping process into two steps: computation of the transformed coordinates (done once) and interpolation on the image (done for each image). Compared toimwarp, this approach speeds up the whole process significantly for small to medium-sized images, with diminishing returns for larger images.

See Also

Functions

Objects

Introduced in R2017b

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