#2335 photo data -grayscale broken

[Aric]

In 8.5b1, the -grayscale option of the [photo data] command yields a dark but not-quite-black image (variation in the grayscale image can be seen by increasing the -gamma value).

The following code works as expected in 8.4.16 but not in 8.5b1:

package require Img
set img1 [image create photo -file c:/myimage.jpg]
set img2 [image create photo]
$img2 put [$img1 data -grayscale]
set l1 [label .l1 -image $img1]
set l2 [label .l2 -image $img2]
grid $l1 $l2