Resize image - MATLAB imresize (2024)

Table of Contents
Syntax Description Examples Shrink Image By Factor of Two Using Default Interpolation Method Shrink Image Using Nearest-Neighbor Interpolation Resize RGB Image Specifying Size of Output Image Resize Indexed Image Input Arguments A — Image to be resized numeric array | logical array | categorical array scale — Resize factor positive number [numrows numcols] — Row and column dimensions of output image two-element vector of positive numbers X — Indexed image to be resized real, nonsparse numeric array map — Colormap associated with indexed image c-by-3 numeric matrix method — Interpolation method character vector | string scalar | two-element cell array Name-Value Arguments Antialiasing — Perform antialiasing when shrinking an image true | false Colormap — Return optimized colormap "optimized" (default) | "original" Dither — Perform color dithering true (default) | false Method — Interpolation method character vector | string scalar | cell array OutputSize — Size of output image two-element vector of positive numbers Scale — Resize scale factor positive number | two-element vector of positive numbers Output Arguments B — Resized image numeric array | logical array | categorical array Y — Resized indexed image numeric array newmap — Colormap of resized indexed image m-by-3 numeric matrix Extended Capabilities C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™. GPU Code Generation Generate CUDA® code for NVIDIA® GPUs using GPU Coder™. Thread-Based Environment Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool. GPU Arrays Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™. Version History R2019a: Supports categorical images See Also Topics MATLAB Command Americas Europe Asia Pacific FAQs

Resize image

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Syntax

B = imresize(A,scale)

B = imresize(A,[numrows numcols])

[Y,newmap]= imresize(X,map,___)

___ = imresize(___,method)

___ = imresize(___,Name,Value)

Description

example

B = imresize(A,scale) returns image B that is scale times the size of image A. The input image A can be a grayscale, RGB, binary, or categorical image.

If A has more than two dimensions, then imresize only resizes the first two dimensions. If scale is between 0 and 1, then B is smaller than A. If scale is greater than 1, then B is larger than A. By default, imresize uses bicubic interpolation.

example

B = imresize(A,[numrows numcols]) returns image B that has the number of rows and columns specified by the two-element vector [numrows numcols].

example

[Y,newmap]= imresize(X,map,___) resizes the indexed image X where map is the colormap associated with the image.

example

___ = imresize(___,method) specifies the interpolation method used.

___ = imresize(___,Name,Value) returns the resized image where name-value arguments control various aspects of the resizing operation. Specify name-value arguments after all other input arguments.

Examples

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Shrink Image By Factor of Two Using Default Interpolation Method

Open Live Script

Load image into the workspace.

I = imread('ngc6543a.jpg');

Shrink the image by a factor of two.

J = imresize(I, 0.5);

Display the original image and the resized image.

figure, imshow(I), figure, imshow(J)

Resize image - MATLAB imresize (1)

Resize image - MATLAB imresize (2)

Shrink Image Using Nearest-Neighbor Interpolation

Open Live Script

Load an image into the workspace.

I = imread('ngc6543a.jpg');

Shrink the image to 40% of the original size using nearest-neighbor interpolation. This is the fastest method, but it has the lowest quality.

J = imresize(I,0.4,'nearest');

Display the original image and the resized image.

imshow(I)title('Original Image')

Resize image - MATLAB imresize (3)

Resize image - MATLAB imresize (4)

Resize RGB Image Specifying Size of Output Image

Open Live Script

Read an RGB image into the workspace.

RGB = imread('peppers.png');

Resize the RGB image to have 64 rows. imresize calculates the number of columns automatically.

RGB2 = imresize(RGB,[64 NaN]);

Get the size of the resized image.

sz = size(RGB2)
sz = 1×3 64 86 3

Display the original image and the resized image.

imshow(RGB)title("Original Image")

Resize image - MATLAB imresize (5)

imshow(RGB2)title("Resized Image with 64 Rows")

Resize image - MATLAB imresize (6)

Resize Indexed Image

Open Live Script

Read an indexed image into the workspace.

[X,map] = imread("corn.tif");

Increase the size of the indexed image by 50%.

[Y,newmap] = imresize(X,map,1.5);

Display the original image and the resized image.

imshow(X,map)title("Original Indexed Image and Colormap")

Resize image - MATLAB imresize (7)

imshow(Y,newmap)title("Resized Image and Optimized Colormap")

Resize image - MATLAB imresize (8)

Input Arguments

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AImage to be resized
numeric array | logical array | categorical array

Image to be resized, specified as a numeric array, logical array, or categorical array of any dimension. Input must be nonsparse, and numeric input must be real.

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

scaleResize factor
positive number

Resize factor, specified as a positive number. imresize applies the same scale factor to the row and column dimensions. To apply a different resize factor to each dimension, use the Scale name-value argument.

If you specify a resize factor that does not result in integer-length image dimensions, then imresize follows the resizing operation with a call to the ceil function. In other words, the output image has ceil(scale*size(A,1)) rows and ceil(scale*size(A,2)) columns.

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

[numrows numcols]Row and column dimensions of output image
two-element vector of positive numbers

Row and column dimensions of output image, specified as a two-element vector of positive numbers. You can specify the value NaN for either numrows or numcols. In this case, imresize calculates the number of rows or columns for that dimension automatically, preserving the aspect ratio of the image.

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

XIndexed image to be resized
real, nonsparse numeric array

Indexed image to be resized, specified as a real, nonsparse numeric array of positive integers.

Data Types: double | uint8 | uint16

mapColormap associated with indexed image
c-by-3 numeric matrix

Colormap associated with indexed image X, specified as a c-by-3 numeric matrix with values in the range [0, 1]. Each row is a three-element RGB triplet that specifies the red, green, and blue components of a single color of the colormap.

Data Types: double

methodInterpolation method
character vector | string scalar | two-element cell array

Interpolation method, specified as a character vector, string scalar, or two-element cell array. The default value for numeric and logical images is "bicubic". The default value for categorical images is "nearest". Categorical images only support the values "nearest" and "box".

When method is a character vector or string scalar, it identifies a particular method or named interpolation kernel, listed in the following table.

MethodDescription

"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.

Interpolation KernelDescription
"box"

Box-shaped kernel

"triangle"Triangular kernel (equivalent to "bilinear")
"cubic"Cubic kernel (equivalent to "bicubic")
"lanczos2"Lanczos-2 kernel
"lanczos3"Lanczos-3 kernel

When method is a two-element cell array, it defines a custom interpolation kernel. The cell array has the form {f,w}, where f is a function handle for a custom interpolation kernel and w is the width of the custom kernel. f(x) must be zero outside the interval -w/2 <= x < w/2. The function handle f can be called with a scalar or a vector input. For user-specified interpolation kernels, the output image can have some values slightly outside the range of pixel values in the input image.

For more information about the built-in and custom interpolation kernels, see Create and Compare Resizing Interpolation Kernels.

Data Types: char | string | cell

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: B = imresize(A,0.5,Antialiasing=false) does not perform antialiasing when shrinking an image.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: B = imresize(A,0.5,"Antialiasing",false) does not perform antialiasing when shrinking an image.

AntialiasingPerform antialiasing when shrinking an image
true | false

Perform antialiasing when shrinking an image, specified as true or false.

  • If the interpolation method is "nearest", then the default value of Antialiasing is false.

  • If the interpolation method is "box" and the input image is categorical, then the default value of Antialiasing is false.

  • For all other interpolation methods, the default value is true.

Data Types: logical

ColormapReturn optimized colormap
"optimized" (default) | "original"

Return optimized or original colormap for indexed image, specified as one of the following values.

ValueDescription
"original"The output colormap newmap is the same as the input colormap map.
"optimized"imresize returns a new optimized colormap.

The Colormap argument is valid only when resizing indexed images.

Data Types: char | string

DitherPerform color dithering
true (default) | false

Perform color dithering, specified as true or false. In dithering, you apply a form of noise to the image to randomize quantization error and prevent large-scale patterns.

The Dither argument is valid only when resizing indexed images.

Data Types: logical

MethodInterpolation method
character vector | string scalar | cell array

Interpolation method, specified as a character vector, string scalar, or two-element cell array. For details, see method.

Data Types: char | string | cell

OutputSizeSize of output image
two-element vector of positive numbers

Size of the output image, specified as a two-element vector of positive numbers. For details, see [numrows numcols].

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

ScaleResize scale factor
positive number | two-element vector of positive numbers

Resize scale factor, specified as a positive number or two-element vector of positive numbers. If you specify a scalar, then imresize applies the same scale factor to the row and column dimensions. If you specify a two-element vector, then imresize applies a different scale value to each dimension.

If you specify a resize scale factor that does not result in integer-length image dimensions, then imresize follows the resizing operation with a call to the ceil function. In other words, the output image has ceil(Scale(1)*size(A,1)) rows and ceil(Scale(2)*size(A,2)) columns.

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

Output Arguments

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B — Resized image
numeric array | logical array | categorical array

Resized image, returned as a numeric, logical, or categorical array of the same data type as the input image, A.

Y — Resized indexed image
numeric array

Resized indexed image, returned as a numeric array of the same data type as the input indexed image, X.

newmap — Colormap of resized indexed image
m-by-3 numeric matrix

Colormap of the resized indexed image Y, returned as an m-by-3 numeric matrix. By default, imresize returns a new, optimized colormap with the resized image. To return a colormap that is the same as the original colormap, use the Colormap name-value argument.

Extended Capabilities

Version History

Introduced before R2006a

expand all

The imresize function now supports categorical images.

See Also

imresize3 (Image Processing Toolbox) | interp2

Topics

  • Working with Image Types in MATLAB
  • Create and Compare Resizing Interpolation Kernels

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Resize image - MATLAB imresize (9)

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Resize image - MATLAB imresize (2024)

FAQs

How do I resize an image in Matlab? ›

B = imresize( A , scale ) returns image B that is scale times the size of image A . The input image A can be a grayscale, RGB, binary, or categorical image. If A has more than two dimensions, then imresize only resizes the first two dimensions. If scale is between 0 and 1, then B is smaller than A .

How can we resize the image answer? ›

Select the File button, choose Open, pick the image you want to resize and then select Open. 3. On the Home tab, in the Image group, select Resize. *Once the Maintain aspect ratio check box is selected, you only need to enter the horizontal value (width) or vertical value (height).

What is the default Imresize in Matlab? ›

By default, imresize uses bicubic interpolation, but you can specify other interpolation methods or interpolation kernels. You can also specify your own custom interpolation kernel. This example use nearest neighbor interpolation. L = imresize(I,magnificationFactor,"nearest");

How do I resize an image in image Resizer? ›

How to resize an image.
  1. Select. Upload your JPG or PNG to our image resizer tool.
  2. Resize. Choose a size template based on the social platform or add your own.
  3. Continue editing. Instantly download your resized image or keep editing in Adobe Express.

How do I resize an image keeping proportions? ›

If the Shift key is held down whilst moving the handle, then the proportions of the object will be preserved. For example, if I hold Shift and drag the bottom edge upwards to reduce the size by half, then the right edge will automatically move to the left to reduce the width of the object by the same amount.

How do I resize an image in coding? ›

One of the simplest ways to resize an image in the HTML is using the height and width attributes on the img tag. These values specify the height and width of the image element. The values are set in px i.e. CSS pixels.

How can we resize an object answer? ›

Resize a picture, shape, text box, or other object
  1. Select the object.
  2. Hold down CTRL.
  3. Move the mouse pointer over one of the handles and then click and drag the mouse.
  4. Release the mouse button before you release CTRL.

How do I resize a JPEG image? ›

You can also go directly to your image, click on it while pressing "Ctrl", click "Open", and then "Preview." Navigate to the "Tools" option in the menu bar and choose "Adjust Size." Select whether you want to adjust by size or percentage in the "Image Dimensions" window. Adjust your width and height.

How to get image size in MATLAB? ›

[height, width] = size(image); This is because imread stores the RGB values separately (for colour images), resulting in a three dimensional matrix. For example, if you loaded a 500p high, 200p wide colour image, this would result in a 500x200x3 matrix.

How to resize raster MATLAB? ›

Resize the raster using mapresize . Double the length and width of the raster by specifying the scale as 2. Use nearest neighbor interpolation by specifying the interpolation method as 'nearest' . [Z2,R2] = mapresize(Z,R,2,'nearest');

How to do size in MATLAB? ›

size (MATLAB Functions) d = size(X) returns the sizes of each dimension of array X in a vector d with ndims(X) elements. [m,n] = size(X) returns the size of matrix X in separate variables m and n . m = size(X,dim) returns the size of the dimension of X specified by scalar dim .

How do I resize an image without changing the size? ›

To change the image size without stretching it, you should keep the aspect ratio — the proportion between the width and height of the image — the same. Most editing tools have an option to 'maintain aspect ratio' when resizing, which automatically adjusts the height when you change the width, and vice versa.

How is image resizing done? ›

Generally speaking, image resizing comes in two forms: Making the image bigger (upscaling) by increasing the dimensions, adding or stretching pixels, or increasing the file size. Making the image smaller (downscaling) by decreasing the dimensions, subtracting or contracting pixels, or decreasing the overall file size.

How do I fix the size of a figure in MATLAB? ›

All you have to do is to replace the values of startingX startingY Width Height, like the following:
  1. figure('Position',[startingX startingY Width Height]);
  2. % Example with numerical values.
  3. figure('Position',[600 100 1500 1000]);
Jan 30, 2015

How do you resize image and bounding box in MATLAB? ›

Resize Image and Bounding Box

Use imresize to scale down the image by a factor of 2. scale = 1/2; J = imresize(I,scale); Use bboxresize to apply the same scaling to the associated bounding box. bboxResized = bboxresize(bbox,scale);

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