The polynomial fit isn't perfect and we end up with alpha values of 1 instead of 0 when applying the mask. This in turn causes issues on canvas where outputs aren't 100% transparent and individual layer bbox calculations are incorrect.
Previously we used erode/dilate and a Gaussian blur to expand and fade the edges of Canvas masks. The implementation a number of problems:
- Erode/dilate kernel sizes were not calculated correctly, and extra iterations were run to compensate. The result is the blur size, which should have been pixels, was very inaccurate and unreliable.
- What we want is to add a "soft bleed" - like a drop shadow with no offset - starting from the edge of the mask, extending out by however many pixels. But Gaussian blur does not do this. The blurred area starts _inside_ the mask and extends outside it. So it kinda blurs inwards and outwards. We compensated for this by expanding the mask.
- Using a Gaussian blur can cause banding artifacts. Gaussian blur doesn't have a "size" or "radius" parameter in the sense that you think it should. It's a convolution matrix and there are _no non-zero values in the result_. This means that, far away from the mask, once compositing completes, we have some values that are very close to zero but not quite zero. These values are quantized by HTML Canvas, resulting in banding artifacts where you'd expect the blur to have faded to 0% alpha. At least, that is my understanding of why the banding artifacts occur.
The new node uses a better strategy to expand the mask and add the fade out effect:
- Calculate the distance from each white pixel to the nearest black pixel.
- Normalize this distance by dividing by the fade size in px, then clip the values to 0 - 1. The result represents the distance of each white pixel to its nearest black pixel as a percentage of the fade size. At this point, it is a linear distribution.
- Create a polynomial to describe the fade's intensity so that we can have a smooth transition from the masked region (black) to unmasked (white). There are some magic numbers here, deterined experimentally.
- Evaluate the polynomial over the normalized distances, so we now have a matrix representing the fade intensity for every pixel
- Convert this matrix back to uint8 and apply it to the mask
This works soooo much better than the previous method. Not only does it fix the banding issues, but when we enable "output only generated regions", we get a much smaller image. Will add images to the PR to clarify.
This class works the same way as `WithMetadata` - it simply adds a `board` field to the node. The context wrapper function is able to pull the board id from this. This allows image-outputting nodes to get a board field "for free", and have their outputs automatically saved to it.
This is a breaking change for node authors who may have a field called `board`, because it makes `board` a reserved field name. I'll look into how to avoid this - maybe by naming this invoke-managed field `_board` to avoid collisions?
Supporting changes:
- `WithBoard` is added to all image-outputting nodes, giving them the ability to save to board.
- Unused, duplicate `WithMetadata` and `WithWorkflow` classes are deleted from `baseinvocation.py`. The "real" versions are in `fields.py`.
- Remove `LinearUIOutputInvocation`. Now that all nodes that output images also have a `board` field by default, this node is no longer necessary. See comment here for context: https://github.com/invoke-ai/InvokeAI/pull/5491#discussion_r1480760629
- Without `LinearUIOutputInvocation`, the `ImagesInferface.update` method is no longer needed, and removed.
Note: This commit does not bump all node versions. I will ensure that is done correctly before merging the PR of which this commit is a part.
Note: A followup commit will implement the frontend changes to support this change.
Update all invocations to use the new context. The changes are all fairly simple, but there are a lot of them.
Supporting minor changes:
- Patch bump for all nodes that use the context
- Update invocation processor to provide new context
- Minor change to `EventServiceBase` to accept a node's ID instead of the dict version of a node
- Minor change to `ModelManagerService` to support the new wrapped context
- Fanagling of imports to avoid circular dependencies
