imrotate

Rotate image

Syntax

J = imrotate(I,angle)

J = imrotate(I,angle,method)

J = imrotate(I,angle,method,bbox)

Description

J = imrotate(I,angle) rotates image I by angle degrees in a counterclockwise direction around its center point. To rotate the image clockwise, specify a negative value for angle. imrotate makes the output image J large enough to contain the entire rotated image. imrotate uses nearest neighbor interpolation, setting the values of pixels in J that are outside the rotated image to 0 (zero).

You optionally can perform the rotation using a GPU (requires Parallel Computing Toolbox™). For more information, see Image Processing on a GPU.

J = imrotate(I,angle,method) rotates image I, using the interpolation method specified by method.

Note

The 'bicubic' interpolation method may give slightly different results on a GPU and CPU.

J = imrotate(I,angle,method,bbox) rotates image I, where bbox specifies the size of the output image. If you specify 'crop', then imrotate makes the output image the same size as the input image. If you specify 'loose', then imrotate makes the output image large enough to include the entirety of the rotated image.

Examples

Rotate Image Clockwise for Better Horizontal Alignment

Read an image into the workspace, and convert it to a grayscale image.

I = fitsread('solarspectra.fts');
I = rescale(I);

Display the original image.

figure
imshow(I)
title('Original Image')

Rotate the image 1 degree clockwise to bring it into better horizontal alignment. The example specified bilinear interpolation and requests that the result be cropped to be the same size as the original image.

J = imrotate(I,-1,'bilinear','crop');

Display the rotated image.

figure
imshow(J)
title('Rotated Image')

Rotate Image on GPU

Read image into a gpuArray object.

 X = gpuArray(imread('pout.tif'));

Rotate the image, performing the operation on the graphics processing unit (GPU).

Y = imrotate(X,37,'bilinear','loose');

Display the rotated image.

figure; imshow(Y)

Input Arguments

I — Image to be rotated

numeric array | logical array | gpuArray

Image to be rotated, specified as a numeric or logical array.

To perform the computation using a GPU, specify I as a gpuArray that contains a numeric or logical array.

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

angle — Amount of rotation in degrees

numeric scalar

Amount of rotation in degrees, specified as a numeric scalar.

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

method — Interpolation method

'nearest' (default) | 'bilinear' | 'bicubic'

Interpolation method, specified as one of the following values:

Value	Description
'nearest'	Nearest-neighbor interpolation; the output pixel is assigned the value of the pixel that the point falls within. No other pixels are considered.
'bilinear'	Bilinear interpolation; the output pixel value is a weighted average of pixels in the nearest 2-by-2 neighborhood
'bicubic'	Bicubic interpolation; the output pixel value is a weighted average of pixels in the nearest 4-by-4 neighborhood Note Bicubic interpolation can produce pixel values outside the original range.

Data Types: char | string

bbox — Bounding box defining size of output image

'loose' (default) | 'crop'

Bounding box that defines the size of output image, specified as either of the following values:

Value	Description
'crop'	Make output image J the same size as the input image I, cropping the rotated image to fit.
'loose'	Make output image J large enough to contain the entire rotated image. J is larger than I.

Data Types: char | string

Output Arguments

J — Rotated image

numeric array | logical array | gpuArray

Rotated image, returned as a numeric or logical array.

If the image is rotated using a GPU, then J is returned as a gpuArray containing a numeric or logical array.

Tips

• This function changed in version 9.3 (R2015b). Previous versions of the Image Processing Toolbox™ use different spatial conventions. If you need the same results produced by the previous implementation, use the function imrotate_old.

• In some instances, this function takes advantage of hardware optimization for data types uint8, uint16, single, and double to run faster.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• imrotate supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, imrotate generates code that uses a precompiled, platform-specific shared library. Use of a shared library preserves performance optimizations but limits the target platforms for which code can be generated. For more information, see Code Generation Using a Shared Library.

• The method and bbox arguments must be compile-time constants.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Usage notes and limitations:

• The 'bicubic' interpolation mode used in the GPU implementation of this function differs from the default (CPU) bicubic mode. The GPU and CPU versions of this function are expected to give slightly different results.

For more information, see Image Processing on a GPU.