"Negative" effect after using contrast on another computer

I used the contrast effect in photoshop on a few grayscale images to make the black parts of them darker. Then I transferred those images onto another computer, and now these images look like the complete negatives of what they were on the first computer. The black parts are white and vice versa. How do I get rid of this so that the images can appear black and white in the right spots on any computer after using the contrast function?

If you have Photoshop on your other computer, I would open the image in it, then change the mode to RBG and the ctrl+I to invert the image. to change modes go to image, mode and then RBG.