[BUG] GUI image displays mean of zero channels plus data channel

[mrariden]

Before you fill out this form:

Did you review the FAQ?

• Yes, I reviewed the FAQ on the cellpose ReadTheDocs

Did you look through previous (open AND closed) issues posted on GH?

• Yes, I searched for related previous GH issues.

Now fill this form out completely:

Describe the bug

Grayscale image is calculated across blank image channels in GUI, causing saturation to display incorrectly:

cellpose/cellpose/gui/gui.py

Lines 1375 to 1379 in 849ca11

	elif self.color == 4:
	if self.nchan > 1:
	image = image.mean(axis=-1)
	self.img.setImage(image, autoLevels=False, lut=None)
	self.img.setLevels(self.saturation[0][self.currentZ])

To Reproduce

Compare cp3 to cp4 GUI displays for the same image.

Run log

N/A

Screenshots

CP3:

CP4 (incorrect):