J.M.W. Turner's "Slave Ship" as Equiluminant

In Turner's painting the Slave Ship we see a violent seascape with a vessel in the background and the bodies of the dead and dying that have been thrown overboard in the foreground. The fiery sky accents the tumult of the scene but when reduced to gray scale the image becomes almost unintelligible. As in Monet's Impression: Sunrise the sun in the Slave Ship almost disappears from the sky as does the figure of the ship and the bodies in the water.