# 1.7. Image Arithmetic in AstroImageJΒΆ

AstroImageJ can do basic arithmetic with images: add, subtract, multiply, and divide them. To do arithmetic, go to the Process menu, and select either Image Calculator or Image/stack calculator (which you select depends on whether there is the toolbar or an image is on top).

Warning

*Always* have AstroImageJ display the result in a new window; you want to be sure to avoid accidentally overwriting or modifying the original data.

Let’s try a couple things to make sure you understand what the image calculator does.

Todo

- Imagine subtracting an image from itself. What should the result be? Use AstroImageJ to subtract an image from itself. Does the result match your expectaion?
- Imagine dividing an image by itself. What should the result be? Use AstroImageJ to divide an image by itself. Does the result match your expectation.