imsharpen

Sharpen image using unsharp masking

Syntax

B = imsharpen(A)

B = imsharpen(A,Name,Value)

Description

B = imsharpen(A) sharpens the grayscale or truecolor (RGB) image A by using the unsharp masking method.

B = imsharpen(A,Name,Value) uses name-value arguments to control aspects of the unsharp masking.

Examples

Sharpen Image

Read an image into the workspace and display it.

a = imread('hestain.png');
imshow(a)
title('Original Image');

Sharpen the image using the imsharpen function and display it.

b = imsharpen(a);
figure, imshow(b)
title('Sharpened Image');

Control the Amount of Sharpening at the Edges

Read an image into the workspace and display it.

a = imread('rice.png');
imshow(a), title('Original Image');

Sharpen image, specifying the radius and amount parameters.

b = imsharpen(a,'Radius',2,'Amount',1);
figure, imshow(b)
title('Sharpened Image');

Input Arguments

A — Image to be sharpened

grayscale image | RGB image

Image to be sharpened, specified as a grayscale or RGB image.

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

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 = imsharpen(A,Radius=1.5); performs sharpening using a Gaussian lowpass filter with standard deviation 1.5.

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

Example: B = imsharpen(A,"Radius",1.5);

Radius — Standard deviation of Gaussian lowpass filter

1 (default) | positive number

Standard deviation of the Gaussian lowpass filter, specified as a positive number. This argument controls the size of the region around the edge pixels that is affected by sharpening. A large value sharpens wider regions around the edges, whereas a small value sharpens narrower regions around edges.

Example: Radius=1.5

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

Amount — Strength of sharpening effect

0.8 (default) | number

Strength of the sharpening effect, specified as a number. A larger value leads to larger increase in the contrast of the sharpened pixels. Typical values for this parameter are within the range [0, 2], although values greater than 2 are allowed. Very large values for this argument may create undesirable effects in the output image.

Example: Amount=1.2

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

Threshold — Minimum contrast required for a pixel to be considered an edge pixel

0 (default) | number in the range [0, 1]

Minimum contrast required for a pixel to be considered an edge pixel, specified as a number in the range [0, 1]. Larger values (closer to 1) allow sharpening only in high-contrast regions, such as strong edges, while leaving low-contrast regions unaffected. Smaller values (closer to 0) additionally allow sharpening in relatively smoother regions of the image. This argument is useful in avoiding sharpening noise in the output image.

Example: Threshold=0.7

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

Output Arguments

B — Sharpened image

numeric array

Sharpened image, returned as a numeric array of the same size and data type as the input image A.

More About

Sharpening

Sharpness is the contrast between different colors. A quick transition from black to white looks sharp. A gradual transition from black to gray to white looks blurry. Sharpening images increases the contrast along the edges where different colors meet.

Unsharp masking

The unsharp masking technique comes from a publishing industry process in which an image is sharpened by subtracting a blurred (unsharp) version of the image from itself. Do not be confused by the name of this filter: an unsharp filter is an operator used to sharpen an image.

Tips

• If A is a truecolor (RGB) image, then imsharpen converts the image to the L*a*b* color space, applies sharpening to the L* channel only, and then converts the image back to the RGB color space before returning it as the output image B.

Extended Capabilities

C/C++ Code Generation

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

imsharpen supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

Version History

Introduced in R2013a

R2022a: imsharpen function uses new color space conversion operations for RGB images

Behavior changed in R2022a

Starting in R2022a, the imsharpen uses different color space conversion operations to sharpen RGB images. In R2021b and earlier, the imsharpen function performed the color space conversions using the makecform and applycform functions. Starting in R2022a, the imsharpen function performs the color space conversions using the rgb2lab and lab2rgb functions.

The new operations yield different results for sharpened RGB images. If you need to reproduce the old behavior, then you can replace the call to imsharpen with a call to the images.compatibility.imsharpen.r2021b.imsharpen function instead. You do not need to change the input arguments.