Re: Photoshop and Huey: Double color correction?

On Mon, 19 May 2008 08:20:12 -0700 (PDT), André Hänsel wrote:

[re monitor correction]

To turn on the Huey color correction I use the Huey Software where I
can switch from "Uncorrected" to "Corrected" which changes the
appearance of colors immediately.

If it works the same as the i1, this is changing the video card's lookup
table (LUT) that was created by the Huey, but leaving the system display
profile in place. Since the video LUT modifies the hardware settings, it
is like a high tide raising all boats equally, changing the colors
displayed by all apps, whether they are color aware or not.

Indeed when I take a screenshot of a picture that is in the color
profile of my monitor (and not sRGB as before) the measured colors are
the same, regardless of what color profile the image has that I paste
into.

Photoshop copies the RGB values directly from the clipboard into the image.
This will change the color appearance because Photoshop now believes that
these RGB values belong to the image's working space defined by the image's
working color profile, and uses the display profile to convert those colors
from the image's color space to the display space, defined by the display
profile.

Nevertheless could you explain what happens when I screenshot an sRGB
image and leave Huey color correction turned off?

Photoshop converts your sRGB colors to display space. When you do the
screenshot, you copy display space RGB values to the clipboard. Pasting
them back into the sRGB image will put these converted color values back
into the sRGB image space, and they will probably appear slightly different
at that point.

Since the Huey LUT is missing, this will alter the display appearance only.
It does not change the RGB numbers.

By the way, when I remove the screen profile in system control and then
screenshot an sRGB image I have consistent (but probably visibly wrong)
colors.

Photoshop uses a default screen space of sRGB if none is specified in the
display properties. SRGB was designed to match the average monitor, so
it's not surprising that it matches your display fairly well.

Other thigs that color wonks might find interesting:

In the advanced section of Color Settings, there are several options for
dealing with profile mismatches. For opening an image file, there is a
profile mismatch option to "Ask when Opening for images with both
mismatched profiles missing profiles. There is an option for displaying a
warning when a pasted image is tagged with a different profile, but the
missing profile option is not available for pasting. This means that it is
not possible to get a warning when pasting an image from a screenshot - the
pixel values are silently assigned whatever your working profile is.

It is easier to see how things work if you use a more extreme profile, such
as Wide Gamut RGB or ProPhoto RGB. The increase in saturation with these
profiles is so obvious that you will see whether colors are being changed,
and whether they are being displayed correctly or not. The numbers also
change more with these profiles. You can create your own pseudo profiles
with various gamma values, and see if you can predict things like whether
pasting a middle gray from a 1.0 gamma image to a 2.3 gamma image will make
the image darker or lighter.

You mentioned the notion of "accurate colors". I've posted another thread
on the topic of "calibrationism vs by the numbers" that you may find
interesting.

--
Mike Russell - http://www.curvemeister.com
.

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