how can I plot a graph over an image in Matlab?

I want to plot the graph over the 1st image.

Answer 1

[Kevin Holly]

Load Example Image

exampleimage = imread('peppers.png');

Flip the image vertically (y-axis direction will be flipped vertically later)

exampleimage = flipud(exampleimage);

Display image

imshow(exampleimage)

Use hold on so more children can be added to the axes

hold on

Create scatter plot

x=1:20:300;
y=x;
scatter(x,y,'filled','w')

Change y-dir to normal (Note, y-dir is upside down when images are displayed by default)

set(gca,'YDir','normal') %gca stand for get current axes

[DARSHAN KUMAR BISWAS]

I can't understand what is happening in the last line.please explain.

[Kevin Holly]

When you display an image. The y-axis is in the reverse direction by default. If one were to create a scatterplot ontop of the image, it would be at the wrong coordinates. To fix this, I flipped the image and then made the y-axis direction normal. Please see below. I have turn on the axes so the coordinates would be visible.

exampleimage = imread('peppers.png');
imshow(exampleimage)
axis on

figure
imshow(flipud(exampleimage))
axis on

figure
x=1:20:300;
y=x;
scatter(x,y,'filled','k')

figure
imshow(flipud(exampleimage))
hold on
scatter(x,y,'filled','w')
axis on

figure
imshow(flipud(exampleimage))
hold on
scatter(x,y,'filled','w')
set(gca,'YDir','normal')
axis on

[DARSHAN KUMAR BISWAS]

Thank you for explaining and giving a straight forward answer.

[DARSHAN KUMAR BISWAS]

Suppose there are multiple numbers of such images and I have to plot graph over each one of them and display all of them together. How can I do it?

[Rik]

Do you want to put them in subplots, or do you want to put all images in the same axes?

[Adam Danz]

The question is continued here:

https://www.mathworks.com/matlabcentral/answers/1753860

[Vaughan Clarkson]

I have a slight variation on the original question which has bugged me for years.

What if (a) the image you're wanting to plot over the top of is larger than your screen and (b) you afterwards want to retrieve the modified pixel data in the original image size?

The problem I run into with Kevin's otherwise excellent solution is that, if the image is larger than the screen size, the imshow command will resize it to fit the screen.

Answer 2

[Adam Danz]

Plot the image using image or imagesc or some other image function that allows you to specify the x and y values of the image. That way you set the image coordinates to the data coordinates.

Then just hold on and plot the data into the same axes.

Note that image functions flip the y axis so you may need to flip it back to normal using set(gca, 'YDir','Normal') or flip your data when you plot it.

If you have additional questions, share the code you've got so far and let us know specificially where you're stuck.

[DARSHAN KUMAR BISWAS]

a=imread('F:\Google drive\6.Internship\surge\Core Internship\IMG_0.jpg');

b=imread('F:\Google drive\6.Internship\surge\Core Internship\IMG_20.jpg');

c=a(:,:,3)-b(:,:,3);

imadjust(c);

H=fspecial("average",10);

cAvg=imfilter(c,H);

max(max(c));

min(min(c));

no_row=size(c,1);

no_col=size(c,2);

Xbox=50;

P=floor(no_col/Xbox);

k=zeros(1,4857);

x=linspace(1,Xbox,Xbox);

q=zeros(453,4857);

y=linspace(1,Xbox,Xbox);

for i=1:453

for j=1:4857

if cAvg(i,j)>10

q(i,j)=cAvg(i,j);

else

q(i,j)=5;

end

end

end

l=zeros(45,Xbox);

for m=1:45

for n=1:Xbox

l(m,n)=mean(mean(q(((m-1)*10+1):10*m,((n-1)*24+1):P*n)));

end

end

for i=1:Xbox

p=l(:,i);

for j=1:45

if p(j)>=10

o(i)=j;

break

else o(i)=45;

end

end

end

for i=1:Xbox

v=((45-o)*20)/45;

end

plot(y,v,'Bx')

[DARSHAN KUMAR BISWAS]

For the graph and the image, the y-axis values are opposite to each other.

Answer 3

[Rik]

You need to use the same axes. The easiest solution is to use hold, probably the line below will already do what you need:

hold(gca,'on')

[DARSHAN KUMAR BISWAS]

a=imread('F:\Google drive\6.Internship\surge\Core Internship\IMG_0.jpg');

b=imread('F:\Google drive\6.Internship\surge\Core Internship\IMG_20.jpg');

c=a(:,:,3)-b(:,:,3);

imadjust(c);

H=fspecial("average",10);

cAvg=imfilter(c,H);

max(max(c));

min(min(c));

no_row=size(c,1);

no_col=size(c,2);

Xbox=50;

P=floor(no_col/Xbox);

k=zeros(1,4857);

x=linspace(1,Xbox,Xbox);

q=zeros(453,4857);

y=linspace(1,Xbox,Xbox);

for i=1:453

for j=1:4857

if cAvg(i,j)>10

q(i,j)=cAvg(i,j);

else

q(i,j)=5;

end

end

end

l=zeros(45,Xbox);

for m=1:45

for n=1:Xbox

l(m,n)=mean(mean(q(((m-1)*10+1):10*m,((n-1)*24+1):P*n)));

end

end

for i=1:Xbox

p=l(:,i);

for j=1:45

if p(j)>=10

o(i)=j;

break

else o(i)=45;

end

end

end

for i=1:Xbox

v=((45-o)*20)/45;

end

plot(y,v,'Bx')