2D Interpolation (Linear and spline) of a greyscale image

Hi Guys,

I have a grey scale image (shown below):

http://www.qfpost.com/download.do?get=f8295c24e09fe632b90a1d09ae5ac69a

Which I wish to interpolate to give 10 times the number of pixels - This is so I can find the edge of the beam when using a white-black intensity graph across the image as the edge is not exactly on a pixel - after carrying out a Canny edge detection.

The following code:

ZI = interp2(X,Y,Z,XI,YI,method)

seems to be the code I require where method will be 'linear' etc, however, I am not sure what the values X,Y,Z,XI and YI should be.

I guess that Z is my image, and the X and Y are co-ordinates of some kind but how would I determine then? I think it has something to do with meshgrids but I do not know very much about such techniques.

Any help would be much appreciated! Thanks, Graham

[Graham Boag]

Here is a picture of the graph of intensity across the beam...the edge is halfway down between the two points marked - which are the pixels that the edge lies between.

http://www.qfpost.com/download.do?get=37962f06f12de583c833deaa40bf3b30

[Graham Boag]

Also, the image is 256 by 256 pixels

[Deepshikha Bhargava]

did you find the solution?

[Image Analyst]

Yes. Scroll down the page and see the Answer with the green check mark, meaning he accepted that answer.

Answer 1

[Sean de Wolski]

Z is your image. You'll want to convert it to double for the interpolation and then back to uint8 or whatever other class after:

 I = your_image;
 class_of_I = class(I);
 [x y] = meshgrid(1:256);
 [xi yi] = meshgrid(1:0.1:256);
 class_of_I
 New_Image = cast(interp2(x,y,double(I),xi,yi,'linear'),class_of_I);

[Sean de Wolski]

PS. I (and probably others) don't trust the website you're using for image downloading. Try uploadhouse.com or tinypic or something that doesn't involve a download with all sorts of other products advertised.

[Graham Boag]

Sure no problem, Was just the first website I found that worked. Ill give the coding a try just now thanks! Graham

[Graham Boag]

>> I = 'f_000014';

class_of_I = class(I);

[x y] = meshgrid(1:256);

[xi yi] = meshgrid(1:0.1:256);

class_of_I

New_Image = cast(interp2(x,y,double(I),xi,yi,'linear'),class_of_I);

class_of_I =

char

??? Error using ==> interp2 at 147

When Z is a vector, X and Y must also be vectors.

Hmm, I still seem to be getting some errors, it doesn't seem to like me!

[Graham Boag]

Do you think the image is just to complex for the coding or is it just a basic problem that I probably can't see? Thanks, Graham

[Graham Boag]

Do you think the image is just to complex for the coding or is it just a basic problem that I probably can't see? Thanks, Graham

[Sean de Wolski]

You've defined I as a string not a numeric matrix!

I = imread('f_000012');

or dicomread/load/etc

[Graham Boag]

Aaah I will learn the in's and out's of matlab some day I hope!

On another note, you sir are a genius! It works - Thanks! Graham

[Graham Boag]

It does show me the new_image but also it says:

Warning: Image is too big to fit on screen; displaying at 25%

> In imuitools\private\initSize at 73

In imshow at 262

Is there a way I can save the full image to avoid the warning?

[Graham Boag]

I got it, sorry, nevermind!

imwrite(New_Image, 'new.tif')

seems to work! Thanks again for all your help with this problem Sean!

Answer 2

[Sean de Wolski]

X,Y are the results of:

 [X Y] = meshgrid(1:256)

Xi, Yi are the locations that you want an interpolated value at, for your example:

 [Xi Yi] = meshgrid(1:0.1:256);
 %SCd

[Graham Boag]

Excellent thanks! I was thinking it would be more complicated than that. Although what would Z refer to, I can't imagine a 3d co-ordinate from my image or do I just not include it?

[Graham Boag]

I seem to get the following error when I type my code:

ZI = interp2(X,Y,Z,Xi,Yi)

??? Error using ==> times

Integers can only be combined with integers of the same

class, or scalar doubles.

Error in ==> interp2>linear at 354

F = ( arg3(ndx).*(onemt) + arg3(ndx+1).*t ).*(1-s)

+ ...

Error in ==> interp2 at 220

zi = linear(ExtrapVal,x,y,z,xi,yi);

[Graham Boag]

Sorry the above answer is when i typed a random value for Z. If I type:

Z = peaks(X,Y);

It seems to run for ages..then i type imshow(ZI) and I get a message saying the image is too big to fit on screen. Have I run the method correctly? Sorry If this is not so clear

Answer 3

[pooja chandrabose]

I need to know how to apply interpolation in a image (biliner,cubic, convolution)plz I need this info as soon as possible

Answer 4

[image-pro]

did you get the answer please tell me the code?

[Image Analyst]

I don't know why all the answers were using interp2 and meshgrid when you can do it simply with imresize()

outputImage = imresize(inputImage, [numDesiredRows, numDesiredColumns]);

Answer 5

[Image Analyst]

I don't know why all the answers were using interp2 and meshgrid when you can do it simply with imresize()

outputImage = imresize(inputImage, [numDesiredRows, numDesiredColumns]);

imresize() has several interpolation schemes you can choose from.

[Bruno Luong]

Because imresize requires image processing toolbox.

[image-pro]

i want to know how to apply newton divided difference interpolation in image