1. CS 450: Introduction to Digital Signal and Image Processing Image Arithmetic

2. Image-Image Operations:

3. Image Addition Used to create double-exposures + =

4. Image Subtraction Useful for finding changes between two images of (basically) the same scene More useful to use absolute difference

5. Background Subtraction “What’s changed?” - = (absolute difference)

6. Motion Use differencing to identify motion in an otherwise unchanging scene. i.e., object motion, not camera motion.

7. Digital Subtraction Angiography Medical imaging technique used to see blood vessels Take one X-ray Inject a contrast agent Take another X-ray Subtract the first (background) from the second (background + vessels)

8. Multiplication Useful for Masking

9. Alpha Blending Addition of two images, each with (0..1) fractional masking weights Useful for transparency, compositing, etc. Color images are often stored as RGB  or RGBA

10. Image Averaging Average multiple images (frames) of the same scene together Useful for removing noise + +... =