Object Space Model Vs Image Space Model

Object Space Model	Image Space Model
This model defines the object with real world dimensions and volumes.	This model defines the object with dimensions of the image, created to be displayed on the display device.
The unit of such dimensions may be in kilometers, meters or even in microns.	It makes use of scaled dimensions.
Object space algorithms are less efficient than image space algorithms.	Image space algorithms are more efficient than object space algorithms.
Object space algorithms are more functional than image space algorithms.	Image space algorithms are less functional than object space algorithms.
Color calculation is done only one time and is retained by it.	Color calculation once done is overwritten later.