I have an image that was taken using a negative color filter long ago, but now I need the normal picture, is there a way to get a good quality of that picture with the actual colors?
The current software I am using is GIMP.
Answer
GIMP has an invert command you can apply to RGB and Grayscale images:
to 
You can acces it through Colors → Invert.
Attribution
Source : Link , Question Author : Nick , Answer Author : Yisela