[Bug]: interpolation_stage="rgba" does not respect array-alpha #28382

Bug summary

Passing interpolation_stage="rgba" to imshow() results in array-valued alphas being ignored.

Code for reproduction

from pylab import *

im = arange(9).reshape(3, 3)
alpha = linspace(0, 1, 9).reshape(3, 3)

subplot(121).imshow(im, alpha=alpha)  # interpolation_stage="alpha"
subplot(122).imshow(im, alpha=alpha, interpolation_stage="rgba")
show()

Actual outcome

Expected outcome

Same image on left and right (interpolation_stage should not matter at all here.

Additional information

No response

Operating system

macos

Matplotlib Version

3.10.0.dev260+g7275ad95ff

Matplotlib Backend

qtagg

Python version

3.12

Jupyter version

no

Installation

git checkout