Thread Subject: how to display IMAGE with custom X, Y axis ticks ?

Hi,

I want to display a Frequency vs Time plot.
The data are stored as an image in an array
and I can display using "imagesc",
but the X and Y labels are in 1000x1000 "pixel" units.

I want to relabel the X axis to represent time,
going from 0 to 10 seconds.

I want to relabel the Y axis to represent frequency,
which goes from 10 Hz to 1000 Hz, on a log scale.

I have looked at the "image()" function and its various
options, but I can't figure out how to do it.

Does anyone out there know how to put custom axis labels on
your image data?

Any help appreciated,
David Jones
djones.nospam@remove.mcmaster.ca

"David " <djones.nospam@remove.mcmaster.ca> wrote in message
<fifjdf$5s6$1@fred.mathworks.com>...

x=linspace(0,10,1000); % 0 to 10 s, 1000 samples
y=logspace(1,3,1000); % 10^1 to 10^3, 1000 samples
imagesc(x,y,data);
set(gca,'Yscale','log','Ydir','normal');

Bruno

"Bruno Luong" <brunoluong@yahoo.com> wrote in message
<fifklg$p53$1@fred.mathworks.com>...
> "David " <djones.nospam@remove.mcmaster.ca> wrote in message
> <fifjdf$5s6$1@fred.mathworks.com>...
>
> x=linspace(0,10,1000); % 0 to 10 s, 1000 samples
> y=logspace(1,3,1000); % 10^1 to 10^3, 1000 samples
> imagesc(x,y,data);
> set(gca,'Yscale','log','Ydir','normal');
>
> Bruno
>

Thanks, ... that *ALMOST* solves my problem,
but there is an error when I try this.

The Y axis labels are not positioned properly.
There seems to be a problem with the "YLim" axis property.
Presumably it is still linear, while the labels are log.

Any suggestions?
I don't know how to update "YLim" appropriately.


You can see for yourself:

N = 32;
data = rand(N,N);
x=linspace(0,10,N); % 0 to 10 s, 64 samples
A = log10(5);
B = log10(60);
y=logspace(A,B,N); % 10^A to 10^B, 64 samples
imagesc(x,y,data);
set(gca,'Yscale','log','Ydir','normal', 'YTick', [5 10 20 30
40 50 60]);
xlabel('Time (sec)'); ylabel('Frequency (Hz)');

"David " <djones.nospam@remove.mcmaster.ca> wrote in message
>
> The Y axis labels are not positioned properly.
> There seems to be a problem with the "YLim" axis property.
> Presumably it is still linear, while the labels are log.

You probably should define tick and label manually like this:

%%%%%%%%%%%%%%%%%

N = 16;
data = rand(N,N);
x=linspace(0,10,N); % 0 to 10 s, 16 samples

Ymin=5; Ymax=60; % Min and max of Y-axis
Ytick=[5 10 20 30 40 50 60];
logy=linspace(log(Ymin),log(Ymax),N);

imagesc(x,logy,data, ...
    'Ydir','normal', ...
    'YTick', log(Ytick), ...
    'YTickLabel', ...
    arrayfun(@num2str, Ytick(:), 'UniformOutput', false));

xlabel('Time (sec)');
ylabel('Frequency (Hz)');

Bruno