Re: [Gimp-user] Is there a single bit that can accidentally flip an image to negative? (not Gimp specific)

[Elle Stone <l elle stone gmail com>]

I'm going to call the image that isn't inverted "right.jpg" and the
image that is inverted (not really inverted, but certainly it's not
right) "wrong.jpg", to avoid typing really long file names.

"Right.jpg" doesn't have an embedded ICC profile. Right.jpg was
created using Gimp, according to the metadata. Upon selecting it to
open it, Gimp displays a normal-looking thumbnail that resembles
"right.jpg". Upon opening it, Gimp automatically assigns the Gimp
built-in sRGB profile and right.jpg looks like you'd expect.

"Wrong.jpg" does have an embedded ICC profile with description "sRGB
IEC61966-2.1". From the embedded profile metadata it appears to be
some version or another of the original  sRGB profile created by
Hewlett-Packard and Microsoft back in 1998. That profile or versions
thereof has been used by almost all imaging software and operating
systems, until V4 profiles started creeping in.

Upon selecting wrong.jpg with Gimp to open it, the thumbnail looks
more or less like the thumbnail for right.jpg, but not exactly (the
colors are washed out, the blue looks purple, the green looks brown).
But upon actually opening it, the colors go all wrong. However, assign
the Gimp built-in sRGB profile in place of the embedded profile and
wrong.jpg now looks very similar to the right.jpg, slightly washed
out, purple instead of blue, brown instead of green, but not
"inverted".

According to the metadata, wrong.jpg is a Photoshop thumbnail. Was the
original image created by Photoshop? Was the thumbnail really created
using Photoshop and extracted using some software?

I've attached a spreadsheet with the embedded metadata for right.jpg,
wrong,jpg, and the argyllcms version of the original MS/HP sRGB
profile, lined up so the metadata fields match. There are very small
differences in the metadata, not enough to explain why wrong.jpg looks
wrong until the Gimp built-in sRGB profile is assigned.Attached is
also a copy of "wrong.jpg" with the argyllcms version of sRGB embedded
so you can see the color differences.

I'm going to try to extract the embedded ICC profile in wrong.jpg to
see what the tone curves look like. Ofnuts is right, the problem (or
at least one problem) is the embedded profile. And the two images
aren't the same to begin with.

Elle Stone
-- 
http://ninedegreesbelow.com - articles on open source digital photography