There are other use cases like suggesting a color palette based on an image upload before it ever gets sent to the server. Something like an admin interface for creating news article pages/blogs that orient around a particular theme.
I agree with the server handling of this if the server is providing the image but I could imagine HTML5 web apps making use of color analysis before the image ever gets sent to the server. JS isn't going away regardless of how much we close our eyes and pretend it's not there.
Fair enough but it's trickier to demo something that requires more elaborate user action. My reach-bag scenario wasn't so contrived actually we had to develop something that would guess a color palette based on a user uploaded picture at Mozilla.
The end product was never realized in that form but our solution included using a 2d canvas also and doing a count of color segments.
I agree with the server handling of this if the server is providing the image but I could imagine HTML5 web apps making use of color analysis before the image ever gets sent to the server. JS isn't going away regardless of how much we close our eyes and pretend it's not there.