imshow: flicker and superposition problem

[jmb]

I am trying to use something like the following code to superimpose a
displayed value over a static image.

I am running into 2 problems with octave 3.2.4 (in Ubuntu12.04.4 32bit)

a) A flickering that would like to suppress as the image is erased and
redisplayed within each cycle of the 'while' loop.

b) if I comment out the imshow(I) inside the loop then the value of
P{amb} overwrites the previously displayed value and soon I get one
black mass of lettering that one cannot read.

I have tried methods that have failed.  Can anybody suggest a fix?

Thanks!


==================================================================
pkg load image;
I = imread ("Schematic.png");
imshow (I);
hold("on");

DisplayPres = true;
while true
#       imshow (I);

        if DisplayPres == true
                Display_Value("P_{amb}=", "bar", P, 0, 0);
                P = P + 0.001;
        endif
        sleep(1);
endwhile
==================================================================