Thread Subject:

How to plot with "imagesc" with logarithmic axis

I need to plot an image, "apple" for example, that both x and y are in log axis.

x = 10.^linspace(log10(0.1),log10(3),10);
y = 10.^linspace(log10(1),log10(5),8);
apple = (y'*x/10);
imagesc(x,y,apple)
set(gca,'YScale','log','YMinorTick','on','Ydir','normal')
axis tight
set(gca,'XTick',([0.1,0.3, 1,3]))
set(gca,'YTick',([1 1.5 1.8 2.1 5]))
  
% lines below won't work
set(gca,'XScale','log')
set(gca,'XMinorTick','on')
set(gca,'YScale','log')
set(gca,'YMinorTick','on')

Thanks for your help,
Rebecca

"Rebecca " <rebecca.shuang@gmail.com> wrote in message <jrlodr$ckr$1@newscl01ah.mathworks.com>...
> I need to plot an image, "apple" for example, that both x and y are in log axis.
>
> x = 10.^linspace(log10(0.1),log10(3),10);
> y = 10.^linspace(log10(1),log10(5),8);
> apple = (y'*x/10);
> imagesc(x,y,apple)
> set(gca,'YScale','log','YMinorTick','on','Ydir','normal')
> axis tight
> set(gca,'XTick',([0.1,0.3, 1,3]))
> set(gca,'YTick',([1 1.5 1.8 2.1 5]))
>
> % lines below won't work
> set(gca,'XScale','log')
> set(gca,'XMinorTick','on')
> set(gca,'YScale','log')
> set(gca,'YMinorTick','on')

IMAGE and IMAGESC can't plot a irregular spaced pixel.

You can merely change the ticklabel.

Use patch or surf to plot irregular spaced data

z=peaks(40);

surf(1:40,1:40,zeros(size(z)),'CData',z, 'Linestyle','none')
view(0,90)
set(gca,'yscale','log')

% Bruno

or you could use imagescnan (from the file exchange). Then you can either fudge your x and y axes:

x_plot=log10(x);
y_plot=log10(y);
imagescnan(x_plot,y_plot,apple)

or use the set(gca...) commands you listed before.

also, instead of 10.^linspace, you may want to have a look at the function logspace

Hi Bruno,

Thanks for the reply.

Imagesc can show both axes in logarithmic with "set(gca,'xoryscale','log')",
but when I do this, the image goes blank.

Since the original data points are evenly located at log axis, I need them be displayed in the same way.

I didn't even know surf can be used for this task. Let me try!

Rebecca


"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <jrmjg3$qrs$1@newscl01ah.mathworks.com>...
>
>
> IMAGE and IMAGESC can't plot a irregular spaced pixel.
>
> You can merely change the ticklabel.
>
> Use patch or surf to plot irregular spaced data
>
> z=peaks(40);
>
> surf(1:40,1:40,zeros(size(z)),'CData',z, 'Linestyle','none')
> view(0,90)
> set(gca,'yscale','log')
>
> % Bruno

"craq" wrote in message <jrmlur$6n8$1@newscl01ah.mathworks.com>...
> or you could use imagescnan (from the file exchange). Then you can either fudge your x and y axes:
>
> x_plot=log10(x);
> y_plot=log10(y);
> imagescnan(x_plot,y_plot,apple)
>
> or use the set(gca...) commands you listed before.
>
> also, instead of 10.^linspace, you may want to have a look at the function logspace


Hi Craq,

You are right. I have to use TickLabel to trick the plot ticks so far...
But the actual need is to display them with accurate logarithmic ticks.
It seems imagesc won't do that for me.

Thank you for replying me.
Rebecca