Rasterize

[MahaB82A]

When is Rasterize necesssary?

As far as I know Rasterize is used to get a sharp image. I am following a tutorial. In that Rasterize is used but I cannot see the image is getting better.

  

[David Arbor · Accepted solution]

All video is raster and not vector based, but you can still work with vector files inside of After Effects. The Continuously Rasterize switch is for those vector layers like Illustrator files. If you scale them past 100% you'll lose quality and your image will appear pixelated. This switch will scale up your image as a vector and then re-rasterize it so it looks sharp. In nearly all cases, if you're not scaling past 100% on a vector layer, then you don't need to use this switch as it does take some additional processing power. 

If you're flipping this switch on a composition, then as the tooltip says, it's a different function called Collapse Transformations. 

[MahaB82A]

Thanks for the explanation.

[Rick Gerard]

If you add a Raster effect to an Illustrator layer, like Drop Shadow, the AI file in After Effects is now pixels, and you should not scale it past about 120% or move it closer to a 3D camera than the zoom value of the camera. If you add a mask to any layer with pixels and you turn on Continuously rasterize, the edges of the mask will remain sharp because the mask is a vector path, but the image will start to seriously degrade if it is scaled much past 120% or moved closer to the camera than the Zoom value.