[Scilab-users] Put an image as the background of an axis

[Philipp Mühlmann]

Well, as I understand you want to plot a function over an background image.

In the case the image pixel number fits the X-Y range of your graph it's
rather simple.

img = ReadImage(IPD_PATH + 'demos\teaset.png');
rows = size(img,'r');cols = size(img,'c');
img(rows,1,:) = (0);        // changing left lower image corner for
checking purpose
                                        // change all 3 colour
channels to get a black pixel
ShowColorImage(img,'');
a = gca();a.axes_visible = ["on","on","off"];x = linspace(1,600,600);y
= 1/2*(x);plot(x,y,'-');a.data_bounds = [0,0;cols,rows];

Two tricky things though:

1st: image coordinates (center of pixel) start at "1", hence there is a gap
of 0.5 between image borders and the axes

2nd: it might become tricky if you want to have negative values on the axis.

Probably there is a way to shift the image to other position within the
coordinate system?


So....not sure if this helps your purpose.

You could also switch "ON" / "OFF" the background image by access the
children of the figure, such as:

IMGPlot = a.Children(2);   // children(2) is the background in this
caseIMGPlot.visible = 'off';


A complete other way would be to combine two images of same size.
Say...background image is img1.

your plot = img2.
Plot the graph and save the figure as a temporary image.

load img1
load temporary image

If size (img1) == size(img2)....You could use SIVP module to linear combine
two images:

img_gray = double(RGB2Gray(img));img2 = zeros(rows, cols) +
255;img2(rows/2,:) = 0;img3 = imlincomb( 0.5, img_gray, 0.4, img2)
// the values here define some kind of transparency.figure();
ShowImage(img3,'');



Best regards,
Philipp




2016-02-08 17:49 GMT+01:00 Jan Åge Langeland <j-lan at online.no>:

>
>
> On 08.02.2016 11:47, antoine.monmayrant at laas.fr wrote:
>
> Hi everyone,
>
> I just failed at placing an image behind a plot.
> I thought that would be easy:
>     - create a figure
>     - create an image uicontrol
>     - create an axis
>     - plot in the axis
>     - set axis.filled="off"
>
> Apparently I was wrong.
> I did not find a way to overlap a plot with transparent background over my
> image.
> It seems that the image is always above the plot no matter what order the
> uicontrol/axes where created.
> I also tried to put both of them inside the same frame, but I did not work
> either.
>
> Any idea?
>
>
>
> ShowImage(im,'J2');
>
> b=newaxes();
> b.filled = "off";
>  plot(a)
>
> JÅ
>
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-- 
There we have the salad.
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