Now to figure out how to make photoshop use that '18% gray' as
a reference... I'll have to check back with google on that.
Hello Rita, Chris, and all other interested parties:
I’ve spent the last 6 months or so lurking on here, soaking up all I
can from your individual and collective experience…what a
treasure chest this collective is!..and I thank you from the
bottom of my heart for all the insight.
I have waited for an opportunity to make my first post for a time
when I can offer something of value. Photography, and subsequent
correction in Photoshop, is an area I can help with.
The very short answer for using the 18% grey card as a reference in
Photoshop is to click it with the grey eyedropper (the middle one)
in either the levels or curves palettes.
Now here’s a little more that you should know about how
this stuff works, and how you can make it work better for you.
If you double-click on the eyedroppers in either the levels or
curves palettes (black, grey, and white) you can set what the values
for those eyedroppers are. By default in Photoshop there are 255
levels of grey: ‘0’ being pure black, and ‘255’ being pure white. The
grey, therefore, is ‘128’, or what is referred to as middle grey.
Middle grey is also the value on an 18% grey card (don’t ask, just
accept that it is). But there are a couple other things you need to
understand before blindly clicking those values in your photo:
First of all, your eyedropper could be sampling 1 single pixel
(‘point sample’), an average of 3x3 pixels (‘3x3 average’), an
average of 5x5 pixels (‘5x5 average’), or any of several other
settings. So when you click on that black area in your photo to
establish your shadow zone, remember that if your eyedropper is set
point sample, you could be clicking on color noise in the shadow, and
that will indeed throw off the colors in your photo. Most people set
the eyedropper to 3x3 average. That way you are getting an average of
the pixels in the area you click, but it’s not sampling too wide a
range. To set the sample range of your eye dropper, just select it
in the tool box and set the sample range up top in the options bar.
Next, defining the values for the eyedroppers depends on your
intended final output for your photos. Will they be viewed
exclusively on screen, will they be printed on your inkjet, or are
they intended for a brochure or some other 4-color process printed
piece? You need to know this because each of these output methods has
limits as to how dark or light an image will print with detail
intact. Suffice it to say that a printed value of 255 (pure white)
will show no detail at all. Neither will 0 (pure black). Most people
set the black value at about 4-6, and white to around 246. Also, and
this is important, when you are sampling these values in your
photograph, you are NOT sampling blown out white values nor are you
sampling totally black shadows. The idea is that you sample the
brightest white and the darkest shadow that still has detail.
There is a normal order to this process: First you establish your
shadow zone, then you do your highlights, and then you do your grey
The black and white eyedroppers are for setting contrast. They set
the range of values between your shadows and highlights. For color
photos, the grey eyedropper is the most important…and the one that
can, in one click, eliminate a color cast. However, to get this
result, you MUST be sampling an area in your photo that should be
neutral grey, or you will just be introducing a different color cast
to the photo by forcing a color that shouldn’t be neutral middle grey
to be neutral middle grey…and all other colors will fall in line
with that false grey. A failsafe way to make sure you have a known
neutral gray in your image is to standardize a shot by putting an 18%
grey card in the frame. That way you have a known neutral to sample.
That’s the medium long answer. Good luck, and I hope it helps.
Rachel L. Naugle