If the gAMA chunk is being handled properly, these five images
should all look alike. If the gAMA chunk is being ignored, they
will be increasingly dark from top to bottom. (There is some round-off error at the extremely high gamma settings, so the last image in the five is all black on the right hand side. This does not occur in the real-world range of gamma settings, only on this test.)
Like this: 
This one should be too light.
This one should be too dark.
