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Photoshop and Color Calibrated Card

 
 
Colin D
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      08-16-2005


Uhler wrote:
>
> Hi All,
>
> I saw a magazine article that showed a color calibration card and
> Photoshop plugin combination to help correct colour.
>
> The color calibration card was three colours, black, white, and 18%
> grey. The idea was to include this card in one of your pictures, then
> the plugin could correct for the color for the entire set of pictures
> in that particular series.
>
> I've done many searches, but I can't find who makes it.
>
> Is this a good way of achieving good color? is there a better way of
> accomplishing the same thing?
>

I don't know of any PS plug-ins for color correction, PS has several
ways of doing that built-in to the program itself.

I think the idea of the black/gray/white card is for use with the Levels
and/or Curves tool, both of which have three eye-dropper symbols,
labelled 'set black point', 'set gray point' and 'set white point'.

Most users seem to use only the gray point dropper, by choosing a spot
in the image which should be neutral gray, like an included gray card
and clicking with the gray dropper in that area. This has the effect of
converting that color to neutral gray, and color-correcting the entire
image accordingly, quick and easy - mostly. Note this dropper only
alters color balance, not luminance levels.

The black and white droppers act a bit differently. The idea with those
is to click the white dropper on an area in the image that should be
peak white, and the black dropper on an area that is to be total black.
Each of these droppers then adjusts the image brightness to produce peak
white or total black in the chosen areas, and modifying all the
luminance levels in between. This effect is like dragging the pointers
under the histogram to set black and white points without altering the
image color balance.

The idea behind the three-shade card then is to set not only the gray
balance, but to set black and white points as well, especially in a
low-contrast image that has no total black or peak white in the image.
Using the card to set these points should ensure that the tonal range of
the image is correct.

Colin D.
 
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Bill Hilton
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      08-16-2005
>roland writes ...
>
>For digital the white side is becoming a big deal. You sometimes
>need to shoot something white to zero the white balance


If you mean "to set the custom white balance" then try this experiment
.... set the in-camera custom white balance with the white side and take
a couple of shots, then set the custom white balance again using the
gray side of the card and take a couple of shots. You'll see that it
doesn't make a difference whether you use the white or gray sides to
define custom white balance, so long as both are neutral. It's
actually easier to make a neutral gray side than a neutral white side.

Bill

 
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Bill Hilton
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      08-16-2005
> roland writes ...
>
>Pictureline said they had to go to some other company to get
>Gray Cards, and the ones they could find were only Gray Cards
>with instructions on the other side ...
>Amazon may still have some of the old Kodak onese left as they
>are not a high volume photo dealer.


I don't know who "Pictureline" is but B&H Photovideo is definitely a
"high volume photo dealer" and they are still stocking Kodak gray cards
with the 90% reflectance white side, three cards for $15 ...
http://www.bhphotovideo.com/bnh/cont...ughType=search

Bill

 
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Bill Hilton
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      08-16-2005
> Colin D. writes ...
>
>The idea behind the three-shade card then is to set not only the gray
>balance, but to set black and white points as well, especially in a
>low-contrast image that has no total black or peak white in the image.


That's a good point Colin, a better answer than I gave about just
setting the white balance with the gray card For anyone doing it
this way (setting all three points) I'd suggest working in 16
bit/channel mode since you may end up with some radical tonal shifts.

Bill

 
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