MATLAB Central Newsreader - How to find Horizontal & Vertical Gradients?

Re: How to find Horizontal & Vertical Gradients?

dvt — Mon, 07 Jan 2008 18:23:52 -0500

Selwyna Bas wrote:
> dvt <dvt+usenet@psu.edu> wrote in message <flovn7
> $102o$1@f04n12.cac.psu.edu>...

>> x = rand(10);
>> i = 3:8;
>> j = 3:8;
>> DH(i,j) = abs( x(i,j-2) + x(i,j+2) - 2*x(i,j) ) +...
>> abs( x(i,j-1) - x(i,j+1) );
>> DV(i,j) =abs( x(i-2,j) + x(i+2,j) - 2*x(i,j) ) +...
>> abs( x(i-1,j) - x(i+1,j) );
>> mask = ((DH+35)< DV);
>> G(i,j) = ( x(i,j-1) + x(i,j+1) ) /2 +...
>> ( 2*x(i,j) - x(i,j-2) - x(i,j+2) )/4;
>> G = mask .* G;

> What is the meaning of G = mask .* G;

mask is a variable containing ones where DH+35<DV, zeros elsewhere.
Multiplying mask by G leaves nonzero values in the matrix G wherever
DH+35<DV, and zeros elsewhere. If you don't want zeros elsewhere, you
can modify the definition of mask... maybe you'd rather have NaN?

> Also explain whats the neccesity of this?
> x = rand(10);

x is a 10x10 random matrix; the code should calculate the gradient of
that matrix. You shouldn't need that line, since you already have a
matrix to operate upon. Note that the rest of the code assumes a 10x10
matrix, since i and j are 3:8. You'll have to modify to suit your needs.

BTW, I don't like using i and j as variables, since I often use them in
complex numbers. I usually use ii and jj instead.

>> Ga = zeros(10); %preallocate
>> DHa = Ga;
>> DVa = Ga;

oops... those three lines are unnecessary.

--
Dave
dvt at psu dot edu

Re: How to find Horizontal & Vertical Gradients?

Selwyna Bas — Sun, 06 Jan 2008 17:16:18 -0500

What is the meaning of G = mask .* G;
Also explain whats the neccesity of this?
x = rand(10);
> Ga = zeros(10); %preallocate
> DHa = Ga;
> DVa = Ga;
pl explain..
Thanku for your help

Re: How to find Horizontal & Vertical Gradients?

Selwyna Bas — Sun, 06 Jan 2008 08:49:53 -0500

dvt <dvt+usenet@psu.edu> wrote in message <flovn7
$102o$1@f04n12.cac.psu.edu>...
> selvi wrote:
> > Hi,
> > I want to implement the following Equations in
MATLAB to find hori
> > & Vert Gradient.
> >
> > DH = | x(i , j-2) + x(i ,,j+2) - 2x(i, j) | + | x
(i,,j-1) - x(i,,j
> > +1) |
> >
> > DV = | x(i-2, j) + x(i+2,,j) - 2x(i, j) | + | x(i-1,
j) - x(i+1,,j)
> > |
> >
> > If(DH+35< DV)
> >
> > G={ [ x(i,,j-1) + x(i,,j+1) ] /2 } + { [ 2x(i,
j) - x(i , j-2)
> > - x(i ,,j+2) ]/4}
>
> If I understand your question, try something like the
following:
>
> x = rand(10);
> Ga = zeros(10); %preallocate
> DHa = Ga;
> DVa = Ga;
>
> i = 3:8;
> j = 3:8;
> DH(i,j) = abs( x(i,j-2) + x(i,j+2) - 2*x(i,j) ) +...
> abs( x(i,j-1) - x(i,j+1) );
> DV(i,j) =abs( x(i-2,j) + x(i+2,j) - 2*x(i,j) ) +...
> abs( x(i-1,j) - x(i+1,j) );
> mask = ((DH+35)< DV);
> G(i,j) = ( x(i,j-1) + x(i,j+1) ) /2 +...
> ( 2*x(i,j) - x(i,j-2) - x(i,j+2) )/4;
> G = mask .* G;
>
> As Roger pointed out, you should look into the meanings
of {}, [], and
> () in Matlab.
> --
> Dave
> dvt at psu dot edu

What is the meaning of G = mask .* G;
Also explain whats the neccesity of this?
x = rand(10);
> Ga = zeros(10); %preallocate
> DHa = Ga;
> DVa = Ga;
pl explain..
Thanku for your help

Re: How to find Horizontal & Vertical Gradients?

dvt — Sat, 05 Jan 2008 22:18:12 -0500

selvi wrote:
> Hi,
> I want to implement the following Equations in MATLAB to find hori
> & Vert Gradient.
>
> DH = | x(i , j-2) + x(i ,,j+2) - 2x(i, j) | + | x(i,,j-1) - x(i,,j
> +1) |
>
> DV = | x(i-2, j) + x(i+2,,j) - 2x(i, j) | + | x(i-1, j) - x(i+1,,j)
> |
>
> If(DH+35< DV)
>
> G={ [ x(i,,j-1) + x(i,,j+1) ] /2 } + { [ 2x(i, j) - x(i , j-2)
> - x(i ,,j+2) ]/4}

If I understand your question, try something like the following:

x = rand(10);
Ga = zeros(10); %preallocate
DHa = Ga;
DVa = Ga;

i = 3:8;
j = 3:8;
DH(i,j) = abs( x(i,j-2) + x(i,j+2) - 2*x(i,j) ) +...
     abs( x(i,j-1) - x(i,j+1) );
DV(i,j) =abs( x(i-2,j) + x(i+2,j) - 2*x(i,j) ) +...
     abs( x(i-1,j) - x(i+1,j) );
mask = ((DH+35)< DV);
G(i,j) = ( x(i,j-1) + x(i,j+1) ) /2 +...
     ( 2*x(i,j) - x(i,j-2) - x(i,j+2) )/4;
G = mask .* G;

As Roger pointed out, you should look into the meanings of {}, [], and
() in Matlab.
--
Dave
dvt at psu dot edu

How to find Horizontal & Vertical Gradients?

selvi — Sat, 05 Jan 2008 16:40:48 -0500

Hi,
I want to implement the following Equations in MATLAB to find hori
& Vert Gradient.

DH = | x(i , j-2) + x(i ,,j+2) - 2x(i, j) | + | x(i,,j-1) - x(i,,j
+1) |

DV = | x(i-2, j) + x(i+2,,j) - 2x(i, j) | + | x(i-1, j) - x(i+1,,j)
|

If(DH+35< DV)

G={ [ x(i,,j-1) + x(i,,j+1) ] /2 } + { [ 2x(i, j) - x(i , j-2)
- x(i ,,j+2) ]/4}