The probable reasons this app failed, and any app that competes with PS will (regardless of how well it tackles the resolution independence/feedback speed issue): are two things:
1. Workflow must match PS 1:1 for the majority of everyday image editing operations.
People that use PS are mostly creative folks who do no understand image editing from a technical perspective. Solving a problem (a use case) to them means to internalize a workflow.
Mastering a 'deep' app like PS this way takes years.
If you write a competitor to PS and dont honor this experience that took your target users years, often over a decade to aquire, you're shooting yourself in the foot too hard to ever gain enough momentum on a market that is dominated by PS (resp. its users).
This is imho also the reason why Adobe hasn't touched basic workflow in PS, ever. Because if they did this, they risked alienating users and driving them to test a competitor's product.
Recall when Apple 'improved' the UI/workflow of FinalCut Pro? The screams of outrage echoing through the web? :)
2. Feature set must be more or less identical to PS. You can 'plus' in some areas but you can't 'minus'.
If you have a use case that is not covered by your app but by PS and it is even used by the average target user only once a week in PS, this will be enough reason for them to not consider your app a worthwhile alternative, even if you do get 1. right.
1. is not too hard to do, engineering wise. But 2. is a huge task. PS simply has a lot of features.
1. Workflow must match PS 1:1 for the majority of everyday image editing operations. People that use PS are mostly creative folks who do no understand image editing from a technical perspective. Solving a problem (a use case) to them means to internalize a workflow. Mastering a 'deep' app like PS this way takes years. If you write a competitor to PS and dont honor this experience that took your target users years, often over a decade to aquire, you're shooting yourself in the foot too hard to ever gain enough momentum on a market that is dominated by PS (resp. its users).
This is imho also the reason why Adobe hasn't touched basic workflow in PS, ever. Because if they did this, they risked alienating users and driving them to test a competitor's product. Recall when Apple 'improved' the UI/workflow of FinalCut Pro? The screams of outrage echoing through the web? :)
2. Feature set must be more or less identical to PS. You can 'plus' in some areas but you can't 'minus'. If you have a use case that is not covered by your app but by PS and it is even used by the average target user only once a week in PS, this will be enough reason for them to not consider your app a worthwhile alternative, even if you do get 1. right.
1. is not too hard to do, engineering wise. But 2. is a huge task. PS simply has a lot of features.