how to add grid to imagesc?

clear all

clc

a=rand(20,50)

x=linspace(-1,1,20)

y=linspace(-1,1,50)

imagesc(x,x,a)

I would like to add grid only at the border of every pixel in a way wen I zoom in only the initial grid appear

can someone help me with this.

thank you in advance

[yanqi liu]

only at the border of every pixel

may be use meshgrid and mesh to plot over image

Answer 1

[DGM]

It depends how you want to visualize the data. Tools like imshow() or imagesc() represent the data points at the center of each facet in the displayed image. Tools like pcolor() represent the data at the vertices. If the latter is what you intend, then just use pcolor() instead of imagesc().

If you actually want the matrix represented as an image, then you'll have to create the grid. One way would be to just overlay a mesh plot.

s = [4 5]; % [y x]
xrange = [-1 1]; % imagesc only needs the endpoints
yrange = [-1 1];

a = rand(s);

dx = diff(xrange)/(s(2)-1);
dy = diff(yrange)/(s(1)-1);
xg = linspace(xrange(1)-dx/2,xrange(2)+dx/2,s(2)+1);
yg = linspace(yrange(1)-dy/2,yrange(2)+dy/2,s(1)+1);

hi = imagesc(xrange,yrange,a); hold on
hm = mesh(xg,yg,zeros(s+1));
hm.FaceColor = 'none';
hm.EdgeColor = 'k';

You might try to do it by setting the grid properties of the axes, but you'll have to contend with the ticklabels if you do that.

As to how you make the added grid appear only at certain zoom levels, you'd have to create some sort of custom callback to do that. I'll leave that to someone else.

[Rabih Sokhen]

thank you DGM

[Rabih Sokhen]

Hello DGM

how can i add some transparency to the grid in a way the grid will not hide the figure in the case of a large array?

thank you in advance

[DGM]

You can try doing

hm.EdgeAlpha = 0.2; % pick some value

which will make the grid lines transparent, but adding alpha to plot objects tends to make plot manipulation laggy (at least for me, it does). It'll still make large images darker though.

If you don't intend on zooming in on larger images, you might just conditionally disable the grid lines if the image is larger than some particular size.

[Rabih Sokhen]

hy Dgm

i still have one more question

your code work very well

But how can I stop interaction between the "brush/data" and the grid line wen i use the brush in the figure to see point?

[DGM]

I messed around with that for a while and I don't know if it's possible. As far as I know, there is no way to restrict the brush to a particular object in a figure. At least in the version I'm using (R2019b), the data brush doesn't even interact with the image object alone, so the only brushable thing is the mesh. Unless something has changed (or if you've added other objects to the figure), then I don't know what you're trying to use the brush on. Strangely, the datatip tool seems to only work on the image, but not the mesh.

If the brush does interact with the image in newer versions, you could always use the xg and yg vectors to set the xticks and yticks of the parent axes. That way you could use the axes grid instead of a mesh overlay. Like I mentioned though, your ticklabels will be a mess to straighten out if you do that.

[Rabih Sokhen]

okay deal

what should i write in my code to use the xg and yg vectors to set the xticks and yticks of the parent axes. ?

thank you in advance

[DGM]

You can try this

s = [4 5]; % [y x]
xrange = [-1 1];
yrange = [-1 1];

a = rand(s);

dx = diff(xrange)/(s(2)-1);
dy = diff(yrange)/(s(1)-1);
xg = linspace(xrange(1)-dx/2,xrange(2)+dx/2,s(2)+1);
yg = linspace(yrange(1)-dy/2,yrange(2)+dy/2,s(1)+1);

hi = imagesc(xrange,yrange,a); hold on
set(gca,'xtick',xg,'ytick',yg)
grid on

Note that the ticklabels correspond to the ticks, and so are necessarily not aligned with the face centers anymore. Also, if you have a larger image, all the tick labels will end up overlapping and turning into a mess. You'll have to decide how you want to discard them. In this example, I'm discarding everything but every fourth label. This strategy obviously depends heavily on the size of the image, the label size, and the figure size.

figure % reset web-plot
s = [40 50]; % [y x]
xrange = [-1 1];
yrange = [-1 1];

a = rand(s);

dx = diff(xrange)/(s(2)-1);
dy = diff(yrange)/(s(1)-1);
xg = linspace(xrange(1)-dx/2,xrange(2)+dx/2,s(2)+1);
yg = linspace(yrange(1)-dy/2,yrange(2)+dy/2,s(1)+1);

hi = imagesc(xrange,yrange,a); hold on

set(gca,'xtick',xg,'ytick',yg)
grid on

% just skip some labels
xtlold = get(gca,'xticklabels');
xtlnew = repmat({''},numel(xtlold),1);
xtlnew(1:4:end) = xtlold(1:4:end);
set(gca,'xticklabels',xtlnew);

ytlold = get(gca,'yticklabels');
ytlnew = repmat({''},numel(ytlold),1);
ytlnew(1:4:end) = ytlold(1:4:end);
set(gca,'yticklabels',ytlnew);

[Rabih Sokhen]

thank you DGM, it works

[Kristoffer Walker]

This is a long-standing RSI issue. This seems like a low-hanging fruit that someone could easily create an API for to make it so much easier for those of us who use and love imagesc. Just add the property "grid", "on". How hard can it be?