How to set conditions to modify the pixel values: (1) at the right(x+1,y)-and-left (x-1,y); and (2) at the top (x,y-1)-and-bottom (x,y+1) with reference to the central pixel (x,y)

Hello!

I need your help to 'conditionally' modify the pixels around an arbitrary selected point/pixel at (x,y) using Matlab. First, please see the following 3 x 3 grid.

top-left (x-1,y-1); 
top-middle (x,y-1); 
top-right (x+1,y-1);

middle-left (x-1,y); 
middle-middle(x,y); 
middle-right (x+1,y);

bottom-left (x-1,y+1); 
bottom-middle(x,y+1); 
bottom-right (x+1,y+1);

As can be seen, in the following code - and thanks to a previously requested/obtained help - I could only modify the pixels at 8 locations adjacent to (x,y) but when I set the following conditions,

     sdh = 0;
        sdv = 0; 
        sdh = abs((1/4)*(Y(1:end-2,1:end-2)-Y(1:end-2,3:end)) + (1/2)*(Y(2:end-1,1:end-2)-Y(2:end-1,3:end)) + (1/4)*(Y(3:end,1:end-2)-Y(3:end,3:end)));
        sdv = abs((1/4)*(Y(1:end-2,1:end-2)-Y(3:end,1:end-2)) + (1/2)*(Y(1:end-2,2:end-1)-Y(3:end,2:end-1)) + (1/4)*(Y(1:end-2,3:end)-Y(3:end,3:end)));

    if  if sdh >= sdv  

    (x+1,y)  = (1/2)*((x+1,y)+(x+2,y));
    (x,y+1) = (1/2)*((x,y+1)+(x,y+2));

    and

    if  sdh < sdv 

   (x,y-1) = (1/2)*((x,y-1)+(x,y-2));
   (x,y+1) = (1/2)*((x,y+1)+(x,y+2));

I can't modify the pixels at the locations (x+1,y) & (x-1,y) when sdh >= sdv; and, at the locations (x,y-1) & (x,y+1) when sdh < sdv, as indicated above. Can you please have a look at the following code and help me, if possible ?

N = 8;

E = [46,38];

X = magic(N);

Y = false(N+2);

for k = 1:numel(E);

Y(2:end-1,2:end-1) = X==E(k);

Z = Y(1:end-2,2:end-1) | Y(3:end,2:end-1) | Y(2:end-1,3:end) | Y(2:end-1,1:end-2) | Y(1:end-2,1:end-2) | Y(1:end-2,3:end) | Y(3:end,1:end-2) | Y(3:end,3:end);

X(Z) = E(k);

end

Answer 1

[Image Analyst]

I think you can do what you want with conv2(), but I cant' figure out what you want. What does sdh and sdv represent? Why are there no comments in the code? Did you strip them out before posting or you just forgot to put them in (both are bad)?

And in words, tell me what "sdh >= sdv" represents, and, again in words, what you want to do if that condition is true. Saying that you want to "modify" the pixel is so vague that it's useless.

And, finally, what is the purpose of the "E" variable?

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

[Gobert]

Thank you very much for your reply and I am so sorry for forgetting to comment as follows: 'sdh' and 'sdv' are Sobel horizontal and vertical derivatives with reference to (x,y). E is a vector containing pixels perceived/detected as edges. If the condition is true, I want to get the pixels values - at the (x+1,y) and (x,y+1) locations (horizontally) (for example:

(x+1,y)  = (1/2)*((x+1,y)+(x+2,y)))

and at the (x,y-1) and (x,y+1) locations (vertically) - replaced by their equivalents as shown above or accordingly.

Please help and many thanks in advance.

[Image Analyst]

Did you read the link I gave you?

I still don't know what you want to do. And I don't know what E is yet.

What's the overall big picture, like you want to find the edges greater than a certain magnitude and threshold and get all parts of the image inside some continuous edge (make a masked image) or whatever... Post your image and script.

[Image Analyst]

To do that equation you'd do

outputImage(y, x+1) = (1/2)*(double(inputImage(y, x+1)) + double(inputImage(y, x+2)));

[Gobert]

Sir,

Again, thanks but I am sorry if you still don't understand my question! E letter represents a vector that contains two elements, picked from the output of magic(8) or magic (N) function because N = 8. Those two elements or numbers are 46 and 38 and are supposedly to represent 'edged pixels' or other selected peak-values. I am not using real image. I want to use the output of magic(8) so I can be able to show the changes (expected) happening around those two numbers/elements (contained in E). There's no other script other than that I posted. I want to explain that situation using the output of magic(8) and show how it works before using real images. Many thanks again for your efforts.

[Image Analyst]

You're right - I still don't understand, perhaps because you didn't answer my questions.

I don't know what the full code is. Is it the top chunk of code that talks about sdf, etc. Or is it the second chunk of code that talks about magic?

In your second chunk of code, Z will be either true or false, not an index. Why are you using Z as an index into X?

[Gobert]

Sir, it is the second. Z is used that way so that pixels at the Y locations in Z can be changed according to the E(k) locations.