How can I get the right image ratio when displaying an image behind a graph?

I want to display an image behind the graph and would like to have to it as a specific X1 vlaue and length which is given by the X2. When I plot it like in my code the image is oversized along the y-axis and it would be nice to get the original ratios of the image. I know how long the object on the image is and I want to scale this to the x-axis (with the X1 and X2) and keep the right widht of the image.

X1 = X
X2 = X+590

figure
a1 = gca;
hold on
image('CData', imread('20-1.jpg'), 'XData', [X1 X2]);
plot(Pos9, TC_V9, '-', 'LineWidth', 2, 'Color', [0 0 0]);

ylabel('TC [W/m/K]', 'Fontweight', 'bold', 'FontSize', 14)
xlabel('Position (mm)', 'Fontweight', 'bold', 'FontSize', 14)
title('C20-1 (67-98 cm) Calc-Sil', 'FontSize', 16)

hold off

Answer 1

[Walter Roberson]

The rule is that the XData you provide will be used as the center of the pixels. You want to shift the boundaries by half of a pixel each.

img = imread('20-1.jpg');
numcol = size(img,2);
X1 = X + numcol/2;
X2 = X + 590 - numcol/2;

fig = figure();
a1 = axes('Parent', fig);
hold(a1, 'on');
image(a1, 'CData', img, 'XData', [x1 X2]);
plot(a1, Pos9, TC_V9, '-', 'LineWidth', 2, 'Color', [0 0 0]);
ylabel(a1, 'TC [W/m/K]', 'Fontweight', 'bold', 'FontSize', 14)
xlabel(a1, 'Position (mm)', 'Fontweight', 'bold', 'FontSize', 14)
title(a1, 'C20-1 (67-98 cm) Calc-Sil', 'FontSize', 16) )
hold(a1, 'off')

[Kim]

Thanks for the answer. It is not exactly what I am searching for. In the meantime I updated my code and this works quiet well, but the problem is that I have to define the values ymin and ymax to fit the image to the y-axis. BUT my question is: is it possible not set the x-values and not the y-values? Because the image doesn´t have the right aspect ratio when I am using the code in that way. Is it possible to size the image by only using the x-values, that the image has its original ratio of length and heigth by defining the length (here with the x-values) ? And I cannot use the x-values for that because they have another dimension as the y-values of the graph otherwise I would not see the graph properly.

Thanks !

Here my updated code:

F1 = imread('20-1.jpg');

X1 = X+590;

yMin = min(TC_V9); 
yMax = max(TC_V9);

figure
a1 = gca;
imagesc([X X1], [yMin yMax], F1);
set(a1, 'Color', 'none');
hold on 
plot(Pos9, TC_V9)
ylabel('TC [W/m/K]', 'Fontweight', 'bold', 'FontSize', 14)
xlabel('Position (mm)', 'Fontweight', 'bold', 'FontSize', 14)
title('C20-1', 'FontSize', 16)