Fading out image not working

[kolibril13]

In the below example,

img.opacity = 0
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

should fade out the cell image, but just disappears suddenly.
Afterwards it should fade in again, and works perfectly for the fade in.

img.opacity =1
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

Any idea what is causing this fadeout bug? Thanks for reading this issue! :)

from napari_animation import Animation
from napari_animation.easing import Easing

import napari
from skimage import data

viewer = napari.view_image(data.cells3d(), channel_axis=1, ndisplay=3)


img = viewer.layers[1]
img.opacity =1
viewer.camera.angles = (0, 0, 90)

animation = Animation(viewer)
viewer.camera.zoom = 1
animation.capture_keyframe(steps=30)

viewer.camera.zoom = 2
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)


viewer.camera.angles = (20, -25, 140)
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

img.opacity = 0 # <- why is this not fading out, but disappearing suddenly?
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

img.opacity =1
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)


viewer.camera.zoom = 1
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

viewer.camera.angles = (0, 0, 90)
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)


animation.animate("hello.mp4", canvas_only=True, fps=60)

napari_video@2023-03-02@12-50-57.mp4

[alisterburt]

hey! interpolation is type based in napari-animation, I assume you are setting integers and napari is not coercing them to floats, could you check if this is indeed the root cause? Would ideally be fixed upstream in napari

[kolibril13]

Good idea!
I just tried

viewer.camera.angles = (20, -25, 140)
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

img.opacity = 0.0
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

img.opacity = 1.0
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

but that did not solve the problem.
In the first example, both values were ints.
And there the fadeout did not work, but the fade in works.
So ints are maybe not the problem.

Just tested again a new script, here I only set the opacity to 0.5, but it completely removes it.
Is there maybe something happening internally that sets the opacity to 0 ?
If yes, then this might be the same bug as #149

from napari_animation import Animation
from napari_animation.easing import Easing

img = viewer.layers[1]
img.opacity =1
viewer.camera.angles = (0, 0, 90)

animation = Animation(viewer)

img.opacity = 1
animation.capture_keyframe(steps=60)

animation.capture_keyframe(steps=120)


img.opacity = 0.5 # <- here, the opacity is set to zero I guess
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

img.opacity = 1.0
animation.capture_keyframe(steps=60, ease=Easing.QUADRATIC)

napari_video@2023-03-02@13-59-08.mp4

[alisterburt]

Thanks for spelunking - I'll have to dig properly to figure this out but the reproducible example is a super useful starting point

[psobolewskiPhD]

I can reproduce this too. It does seem related to #149
Again the viewer_state of key_frames is correct, so I assume it's an interpolation issue with decreasing values.

[psobolewskiPhD]

Ok, here the snippets are the problem actaully. @alisterburt was on the right track with typing issue.
So the snippet has img.opacity=1 This makes starting opacity an int:

In [2]: viewer.layers[-1]._get_state()
Out[2]: 
{'name': 'Image [1]',
 'metadata': {},
 'scale': [1.0, 1.0, 1.0],
 'translate': [0.0, 0.0, 0.0],
 'rotate': [[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]],
 'shear': [0.0, 0.0, 0.0],
 'affine': array([[1., 0., 0., 0.],
        [0., 1., 0., 0.],
        [0., 0., 1., 0.],
        [0., 0., 0., 1.]]),
 'opacity': 1,

This is then stored in the viewer_state and when interpolation is performed, the wrong interpolation is chosen here because the initial value (a) is an int:

napari-animation/napari_animation/interpolation/base_interpolation.py

Lines 70 to 88 in 969fefb

	def interpolate_num(a: Number, b: Number, fraction: float) -> Number:
	"""Linear interpolation for numeric types.
	Parameters
	----------
	a : Number
	initial value
	b : Number
	final value
	fraction : float
	fraction to interpolate to between a and b.
	Returns
	----------
	: numeric type
	Interpolated value between a and b at fraction.
	"""
	number_cls = type(a)
	return number_cls(a + (b - a) * fraction)

So you need to set opacity as a float currently, but this should probably be coerced on the napari side?