Hi folks.  I'm trying to write a piece of code to perform some image manipulation - specifically, to mathematically subtract one image from another, and display the result.  (The program aims to show changes in ground movement over time using aerial or satellite images.)  I'm not having much luck in finding anything in the documentation for this kind of function using images.  Can anyone give me some pointers on how to do this?

Thanks.

 Hi RichardB and welcome to the forum.

Have you got a couple of pictures you can show us as an example of what you are trying to do? What type of file compression are you using as I think this would not be possible with .jpg files?

RichardB said

…I'm trying to write a piece of code to perform some image manipulation - specifically, to mathematically subtract one image from another…

I can't see a ready made function for this in Gambas. So you would either have to cycle through the 2 dimensional array for each of the 2 images, and subtract each value, or maybe call an external script to do the work (maybe using GIMP).

See also:-
https://uk.mathworks.com/help/images/ref/imsubtract.html
/comp/gb.image/image - Gambas Documentation

Here is my very basic test code that seems to work.

Create a new project, make sure component gb.Image is included.

Add 2 textboxes and 1 button. Pre-load the text boxes with the paths of 2 equal sized images (I used jpegs).

(Click to enlarge)

The code:-


I couldn't remember how to create a blank image the right size (for myImage3) so I just copied myImage1 into myImage3.

I hope this helps.

…and here is an example using my code.

The following 2 images where time-lapse photos taken with my trail-cam:

(Click to enlarge)

(Click to enlarge)

…and here is the result…

(Click to enlarge)

only unique pixels in image1 are reproduced in image3.

You can also utilize ImageMagick through SHELL/EXEC.

Here's a forum thread on how to do it with ImageMagick:
Simple subtract - Legacy ImageMagick Discussions Archive

But steve's solution is way cooler  8-)

 Hi all, and thank you for the welcome.

I really appreciate everyone's help, and special thanks to steve - that looks like the sort of solution I've been chasing.  Unfortunately I'm at work at the moment, so I won't be able to test out your code example until I go home.  I'll let you know how it turns out.

Thanks again.
-RB