Adding index to a function.

Hello, I am trying to add an index to a function. I have an ROI on an image. Each time the ROI moves on the image, I want the index to increase by 1. So when I move the ROI for a fourth time i want the index to be equal to 4. I have the index sum = 0, and then when the ROI moves I say sum = sum+1;. However, when I do this, the function repeats and just sets the sum = 0, and so the sum is always equal to 1, instead of increasing by integer values. Does anyone have an idea on how to fix this. I tried putting the sum = 0 line on the outside of the function but then the function doesn't know what sum is and it is undefined.

clear

clc

I = imread('air.jpg');

I = rgb2gray(I);

I = im2double(I);

imshow(I)

roi = drawrectangle('Color','r');

addlistener(roi,'MovingROI',@allevents)

addlistener(roi,'ROIMoved',@allevents)

function allevents(src,evt)

evname = evt.EventName;

I = imread('air.jpg');

I = rgb2gray(I);

I = im2double(I);

sum = 0;

switch(evname)

case{'MovingROI'}

%donothing for now

case{'ROIMoved'}

sum = sum+1

disp(['ROI moved previous position: ' mat2str(evt.PreviousPosition)]);

disp(['ROI moved current position: ' mat2str(evt.CurrentPosition)]);

end

end

Answer 1

[Matt J]

One way is to nest the function inside an outerFunction() and make the accumulator an externally scoped variable. In the example below, I've renamed your accumulator from sum to accum since the latter avoids conflict with the builtin Matlab sum() function.

function outerFunction

accum=0; %<-----------MOVE HERE

I = imread('air.jpg');

I = rgb2gray(I);

I = im2double(I);

imshow(I)

roi = drawrectangle('Color','r');

addlistener(roi,'MovingROI',@allevents)

addlistener(roi,'ROIMoved',@allevents)

function allevents(src,evt)

evname = evt.EventName;

I = imread('air.jpg');

I = rgb2gray(I);

I = im2double(I);

switch(evname)

case{'MovingROI'}

%donothing for now

case{'ROIMoved'}

accum = accum+1

disp(['ROI moved previous position: ' mat2str(evt.PreviousPosition)]);

disp(['ROI moved current position: ' mat2str(evt.CurrentPosition)]);

end

end

end

[Kevin P Meyer]

Thank you so much! I have been stuck on that for a while.Makes sense

Answer 2

[Matt J]

You could also have used a persistent variable.

function allevents(src,evt)

persistent accum

if isempty(accum), accum=0; end %first time called

evname = evt.EventName;

I = imread('air.jpg');

I = rgb2gray(I);

I = im2double(I);

switch(evname)

case{'MovingROI'}

%donothing for now

case{'ROIMoved'}

accum = accum+1

disp(['ROI moved previous position: ' mat2str(evt.PreviousPosition)]);

disp(['ROI moved current position: ' mat2str(evt.CurrentPosition)]);

end

end

[Kevin P Meyer]

Ah, okay. The nested function works well for my applications right now but I may try that way to see how it affects the speed. Do you think I could make my image, I, a persistent variable? Would this mean that the function wouldn't have to read it each time?

[Matt J]

Yes, you can make any variable a persistent variable.