# Diferrence Between Subtraction in ForeGround and Background and Subtract Scalar Volumes

**URL:** <https://discourse.slicer.org/t/diferrence-between-subtraction-in-foreground-and-background-and-subtract-scalar-volumes/23799>\
**Category:** Support\
**Created:** [June 9, 2022, 3:54pm UTC](https://discourse.slicer.org/t/diferrence-between-subtraction-in-foreground-and-background-and-subtract-scalar-volumes/23799 "2022-06-09T15:54:31Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Ayush\_Gupta](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/ayush_gupta/32/15579_2.png) [@Ayush\_Gupta](https://discourse.slicer.org/u/Ayush_Gupta)\
**Post date:** [June 9, 2022, 3:54pm UTC](https://discourse.slicer.org/t/diferrence-between-subtraction-in-foreground-and-background-and-subtract-scalar-volumes/23799/1 "2022-06-09T15:54:31Z")

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Hello there I want to subtract two volumes one is a CT Scan and another is CT Angiography, when I use scalar subtraction I get a different output from subtraction in foreground and background(I registered both the images before subtraction)

Thanks in advance.