Flood Select Tool not working as expected

[codefoster]

I'm pretty new to Affinity Photo, but I've used the Flood Select Tool a lot in the past. It's not working for me, however, on a certain image. If I create a new document and paint a little and then click in my paint with the Flood Select Tool it works, but if I paste an image in and try to use it in the "(image)" layer it doesn't work. If I then merge that image layer down to my pixel layer I'm again able to use the Flood Select Tool to select color areas of the image. Can someone explain what's going on here? Thanks.

[RNKLN]

Right click on the layer - Select 'Rasterize' before you use the Flood Select Tool.

[codefoster]

Thank you. This is counter-intuitive to me since images are rasterized. What's the advantage to maintaining a (somehow) non-rasterized image layer?

[Pšenda]

2 hours ago, codefoster said:

Thank you. This is counter-intuitive to me since images are rasterized. What's the advantage to maintaining a (somehow) non-rasterized image layer?

Image layer is a single object for manipulation with whole image, which retains the original attributes *), Pixel layer is array of separate pixels for their editing.

*) Manipulation with Image layer is non-destructive, rasterization is destructive - image must be recalculated to new size, DPI, ICC,...