Are alpha values determined by some kind of image processing algorithm? or do they have to be set manually
rgrao
https://ciechanow.ski/alpha-compositing this site has a great visualization for alpha compositing with interactive elements as well, I think it might be a useful thing to check out.
keenan
@evannw It used to be that people would just manually "paint" an $\alpha$ channel, but these days there are all sorts of algorithmic techniques (build into tools like Adobe Photoshop) that make the process much less painful. See for instance Poisson matting, where our friend the koala makes an appearance; there have since been methods based on machine learning and so forth. Still, professional artists will probably tell you that the automatic tools don't always do the right thing, and sometimes you have to go in and fix things up by hand.
keenan
@rgrao Nice demo!
L100magikarp
How come alpha isn't just a binary 0-1 mask? I suppose things like strands of hair might require subpixel accuracy, but in that case, it seems like the background color should be blended with the foreground in a way that is inseparable (eg the leaves behind the koala), and yet there are no green artifacts when the koala is pasted.
L100magikarp
@myself, this was pretty much answered in the mini homework!
emmurphy
Are there any related machine learning or image cognition algorithm used to process such alpha channel? Also, the alpha channel is super useful in rendering.
0x484884
In an image like the koala, would you end up with some of the background colors blending with the fur on the edge (giving a halo effect)? It seems like it would be impossible to separate the koala fur from the background when the fur is thin enough that it doesn't cover a single pixel.
auruxy
@emmurphy, there's definitely some research in doing high-resolution image segmentation, that generates what can be thought as the alpha channel of an object. I'll post a link once I find a recent paper!
Are alpha values determined by some kind of image processing algorithm? or do they have to be set manually
https://ciechanow.ski/alpha-compositing this site has a great visualization for alpha compositing with interactive elements as well, I think it might be a useful thing to check out.
@evannw It used to be that people would just manually "paint" an $\alpha$ channel, but these days there are all sorts of algorithmic techniques (build into tools like Adobe Photoshop) that make the process much less painful. See for instance Poisson matting, where our friend the koala makes an appearance; there have since been methods based on machine learning and so forth. Still, professional artists will probably tell you that the automatic tools don't always do the right thing, and sometimes you have to go in and fix things up by hand.
@rgrao Nice demo!
How come alpha isn't just a binary 0-1 mask? I suppose things like strands of hair might require subpixel accuracy, but in that case, it seems like the background color should be blended with the foreground in a way that is inseparable (eg the leaves behind the koala), and yet there are no green artifacts when the koala is pasted.
@myself, this was pretty much answered in the mini homework!
Are there any related machine learning or image cognition algorithm used to process such alpha channel? Also, the alpha channel is super useful in rendering.
In an image like the koala, would you end up with some of the background colors blending with the fur on the edge (giving a halo effect)? It seems like it would be impossible to separate the koala fur from the background when the fur is thin enough that it doesn't cover a single pixel.
@emmurphy, there's definitely some research in doing high-resolution image segmentation, that generates what can be thought as the alpha channel of an object. I'll post a link once I find a recent paper!