convert("LAB") fails for RGB

[tkzv]

What did you do?

Called PIL.Image.Image.convert(mode='LAB') for an RGB image

img = PIL.Image.open('filename.png').convert(mode='LAB')

What did you expect to happen?

Conversion of data to LAB colourspace.

What actually happened?

ValueError: conversion from RGB to LAB not supported

The following code did work:

rgb_lab_transform = PIL.ImageCms.buildTransformFromOpenProfiles(PIL.ImageCms.createProfile('sRGB'), PIL.ImageCms.createProfile('LAB'), 'RGB', 'LAB')
img = PIL.ImageCms.applyTransform(Image.open('filename.png').convert(mode='RGB'), rgb_lab_transform)

What are your OS, Python and Pillow versions?

• OS: Linux, kernel 5.15.32-gentoo-r1
• Python: 3.10.6
• Pillow: 9.2.0

[radarhere]

I've created PR #6647 to resolve this.