Plotting an image, how to show origin tick marks?

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User1234
User1234 2017-1-27
评论： Image Analyst 2017-1-27
I'm trying to show the origin in this plot, but it is not working, any suggestions?
x1 = linspace(-1,1,256);
x2 = x1.';
A = 1;
f1 = (4);
f2 = (3);
ph = pi;
u = A*cos(2*pi*(f1*x1+x2*f2)/2+ph);
figure(1)
imshow(u)
title('Cosine Function, f=(4,3)c/ph')
xlabel('x1[ph]')
ylabel('x2[ph]')
axis on
xticks([0 50 100 150 200 250])
xticklabels({'0','50','100','150','200','250'})
yticks([0 50 100 150 200 250])
yticklabels({'0','50','100','150','200','250'})
In addition to this, I need to make another plot of this 3-d cosine, is there a command I can use with imshow to alter this image to give a perspective shot? Maybe via axis?

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回答（3 个）

Image Analyst
Image Analyst 2017-1-27
You can use imshow and pass in XData and YData. You can use line() to draw across the image at the origin/main axes if you want:
fontSize = 20;
x1 = linspace(-1,1,256);
x2 = x1.';
A = 1;
f1 = 4;
f2 = 3;
ph = pi;
u = A*cos(2*pi*(f1*x1+x2*f2)/2+ph);
imshow(u, 'XData', x1, 'YData', x2);
title('Cosine Function, f=(4,3)c/ph', 'FontSize', fontSize)
xlabel('x1[ph]', 'FontSize', fontSize)
ylabel('x2[ph]', 'FontSize', fontSize)
% Put tick marks at specified locations:
axis on
xticks([-1:0.2:1])
yticks([-1:0.2:1])
% Put lines across the entire image, in the overlay, where the main axes should be.
line(xlim, [0,0], 'LineWidth', 2, 'Color', 'r');
line([0,0], ylim, 'LineWidth', 2, 'Color', 'r');
Adam
Adam 2017-1-27
编辑：Adam 2017-1-27
[0, 0] is not visible on an image axes normally. The origin is at [0.5 0.5] because the first pixel is centred at [1 1], extending out in all directions by 0.5 to meet up with the next pixel.
You could force [0 0] to be on the axes by e.g.
xlim( hAxes, [0 250] )
ylim( hAxes, [0 250] )
but you may well get a small white border round your image in that case as there is no data between 0 and 0.5.
Alternatively you can use the XTickLabel property of axes instead and map and XTick at 0.5 onto a label of 0 and the same with YTickLabel.
It can all get a bit messy though, especially if you allow zooming and panning.
Jan
Jan 2017-1-27
imshow draws the image from the coordinates 1 to 256. Then the data do not contain the 0 and therefore no ticks appear at the origin.
If you use image instead, you can specify the X and Y coordinates.
What do you want to see in the tilted view? A tilted grey image or do you want a 3D graph with the Z position defined by the value of u?
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User1234
User1234 2017-1-27
@Jay Simon Thanks for the info!
As for your followup question I would like to see a 3d graph with the Z position defined by the value of u.
Right now I have something like this but it does not use imshow:
x1 = linspace(0,1,256);
x2 = x1.';
A = 1;
f1 = (4);
f2 = (3);
ph = pi;
u = A*cos(2*pi*(f1*x1+x2*f2)+ph);
b=figure(2);
u2=mesh(x1,x2,u);
colormap hsv;
title('Cosine Function, f=(4,3)c/ph');
xlabel('x1[ph]');
ylabel('x2[ph]');
saveas(b,'A1_3b.png');
Image Analyst
Image Analyst 2017-1-27
Sounds like you want surf() then, not image(), imagesc(), or imshow().

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