directional

imgradient

Gradientmagnitudeanddirectionofanimage

collapallinpage

Syntax

[Gmag,Gdir]=imgradient(I)

[Gmag,Gdir]=imgradient(I,method)

example

[gpuarrayGmag,gpuarrayGdir]=imgradient(gpuarrayI,___)

example

[Gmag,Gdir]=imgradient(GxGy)

example

[gpuarrayGmag,gpuarrayGdir]=imgradient(gpuarrayGx,gpuarrayGy)

example

Description

[Gmag,Gdir]=imgradient(I)returnsthegradientmagnitude,Gmag,andthe

gradientdirection,Gdir,forthegrayscaleorbinaryimageI.

example

[Gmag,Gdir]=imgradient(I,method)returnsthegradientmagnitudeand

directionusingspecifiedmethod.

example

[gpuarrayGmag,gpuarrayGdir]=imgradient(gpuarrayI,___)performsthe

utimageandthereturnvaluesaregpuArrays.

ThissyntaxrequirestheParallelComputingToolbox™.

example

[Gmag,Gdir]=imgradient(GxGy)returnsthegradientmagnitudeanddirection

usingdirectionalgradientsalongthex-axis,Gx,andthey-axis,Gy,suchas

-axispointsinthedirectionof

increasingcolumnsubscriptsandthey-axispointsinthedirectionof

increasingrowsubscripts.

example

[gpuarrayGmag,gpuarrayGdir]=imgradient(gpuarrayGx,gpuarrayGy)performsthe

utxandygradientsandthereturnvaluesare

ntaxrequirestheParallelComputingToolbox.

Examples

collapall

Calculategradientmagnitudeandgradientdirection

Readimageandcomputegradientmagnitudeandgradientdirectionusing

Prewitt'sgradientoperator.

Readimage.

I=imread('');

Calculategradientsanddisplay.

[Gmag,Gdir]=imgradient(I,'prewitt');

figure;imshowpair(Gmag,Gdir,'montage');

title('GradientMagnitude,Gmag(left),andGradientDirection,Gdir(right),

usingPrewittmethod')

axisoff;

Calculategradientmagnitudeandgradientdirection

onaGPU

Readimageandcomputegradientmagnitudeandgradientdirectionusing

Prewitt'sgradientoperator.

Readimage.

I=gpuArray(imread(''));

imshow(I)

Calculategradientsanddisplay.

[Gmag,Gdir]=imgradient(I,'prewitt');

figure,imshow(Gmag,[]),title('Gradientmagnitude')

figure,imshow(Gdir,[]),title('Gradientdirection')

Calculatedirectionalgradientsinadditionto

gradientmagnitudeanddirection

Readimageandreturndirectionalgradients,GxandGy,aswellasgradient

magnitudeanddirection,GmagandGdir,utilizingdefaultSobelgradient

operator.

Readimage.

I=imread('');

Calculategradientsanddisplaythem.

[Gx,Gy]=imgradientxy(I);

[Gmag,Gdir]=imgradient(Gx,Gy);

figure,imshow(Gmag,[]),title('Gradientmagnitude')

figure,imshow(Gdir,[]),title('Gradientdirection')

title('GradientMagnitude(Gmag)andGradientDirection(Gdir)usingSobel

method')

figure;imshowpair(Gx,Gy,'montage');axisoff;

title('DirectionalGradients,GxandGy,usingSobelmethod')

Calculatedirectionalgradientsinadditionto

gradientmagnitudeanddirectiononaGPU

Readimageandreturndirectionalgradients,GxandGy,aswellasgradient

magnitudeanddirection,GmagandGdir,utilizingdefaultSobelgradient

operator.

Readimage.

I=gpuArray(imread(''))

atwhenyouspecifya

gpuArraytoimgradientxy,ultsare

thesameasthepreviouxample.

[Gx,Gy]=imgradientxy(I);

[Gmag,Gdir]=imgradient(Gx,Gy);

figure,imshow(Gmag,[]),title('Gradientmagnitude')

figure,imshow(Gdir,[]),title('Gradientdirection')

figure,imshow(Gx,[]),title('Directionalgradient:Xaxis')

figure,imshow(Gy,[]),title('Directionalgradient:Yaxis')

InputArguments

collapall

I—Inputimagegrayscaleimage|binaryimage

Inputimage,specifiedasagrayscaleorbinaryimage,thatis,anumericor

logical2-Dmatrixthatmustbenonspar.

DataTypes:single|double|int8|int32|uint8|uint16|uint32|logical

gpuarrayI—InputimagegpuArray

Inputimage,specifiedasa2-DgrayscaleorbinarygpuArrayimage.

DataTypes:single|double|int8|int32|uint8|uint16|uint32|logical

method—Gradientoperator‘Sobel'(default)|

‘Prewitt'|'CentralDifference'|

'IntermediateDifference'|‘Roberts'

Gradientoperator,specifiedasoneofthetextstringsinthefollowingtable.

MethodDescription

‘Sobel'

Sobelgradientoperator(default)

‘Prewitt'

Prewittgradientoperator

'CentralDifference',Centraldifferencegradient:dI/dx=(I(x+1)-I(x-1))/2

'IntermediateDifference'

Intermediatedifferencegradient:dI/dx=I(x+1)-I(x)

‘Roberts'

Robertsgradientoperator

DataTypes:char

Gx—Directionalgradientsalongx-axis(horizontal)

matrix

Directionalgradientalongx-axis(horizontal),specifiedasnon-sparmatrix

equalinsizetoimageI,typicallyreturnedbyimgradientxy.

DataTypes:single|double|int8|int32|uint8|uint16|uint32

Gy—Directionalgradientsalongthey-axis

(vertical)matrix

Directionalgradientalongy-axis(vertical),specifiedasnon-sparmatrix

equalinsizetoimageI,typicallyreturnedbyimgradientxy.

DataTypes:single|double|int8|int32|uint8|uint16|uint32

gpuarrayGx—Directionalgradientsalongx-axis

gpuArray

Directionalgradientalongx-axis,specifiedasagpuArray,typicallyreturned

byimgradientxy.

DataTypes:single|double|int8|int32|uint8|uint16|uint32

gpuarrayGy—Directionalgradientsalongthe

y-axisgpuArray

Directionalgradientalongy-axis,specifiedasagpuArray,typicallyreturned

byimgradientxy.

DataTypes:single|double|int8|int32|uint8|uint16|uint32

OutputArguments

collapall

Gmag—Gradientmagnitudematrix

Gradientmagnitude,returnedasanon-sparmatrixthesamesizeas

ofclassdouble,unlesstheinputimageIisofclasssingle,in

whichcaitisofclasssingle.

DataTypes:double|single

gpuarrayGmag—GradientmagnitudegpuArray

Gradientmagnitude,returnedasanon-spargpuArraythesamesizeas

ofclassdouble,unlesstheinputimageIisofclasssingle,in

whichcaitisofclasssingle.

DataTypes:double|single

Gdir—Gradientdirectionmatrix|gpuArray

Gradientdirection,returnedasanonsparmatrixthesamesizeasimageI.

Gdircontainsanglesindegreeswithintherange[-180180]measured

counterclockwifromthepositivex-axis.(Thex-axispointsinthedirection

ofincreasingcolumnsubscripts.)Gdirisofclassdouble,unlesstheinput

imageIisofclasssingle,inwhichcaitisofclasssingle.

WhenIorGxandGyaregpuArrays,GdirisagpuArray.

DataTypes:double|single

gpuarrayGdir—GradientdirectiongpuArray

Gradientdirection,returnedasanonspargpuArraythesamesizeas

ntainsanglesindegreeswithintherange[-180180]

measuredcounterclockwifromthepositivex-axis.(Thex-axispointsin

thedirectionofincreasingcolumnsubscripts.)Gdirisofclassdouble,unless

theinputimageIisofclasssingle,inwhichcaitisofclasssingle.

DataTypes:double|single