Tutorials - Color Management for Photographers - page 317

However, as you start to enter values in either HSB or RGB, the
basics of the CMYK equivalents become clearer. For example,
enter 20 into the S field from the previously set H0/S0/B100
values and notice that a light pink is seen. The RGB values read
R255/G204/B204 and the CMYK values read C0/M26/Y9/B0 .
The highest value is magenta with a bit of yellow. No cyan, no
black. Sounds like a light red or pink, which is exactly what
we see.
8. Click the L radio button and enter L100/a0/b0 ; you end up
with a pure white. Examine the values for RGB as well as
HSB. Enter L0/a0/b0 and you end up with a pure black. The
L value controls luminance, and this is an easy number to
understand. The a-star and b-star settings are more complex.
The numeric scale runs from -127 to 127 for each, making these
far more difficult values to understand. Feel free to move the
small circle in the color palette around and watch the LAB
values update, but I think you'll find that working in RGB and
HSB are far more intuitive but unfortunately not device-
independent.
9. At the top of the palette are two color squares. One represents
the original color the picker had prior to opening this dialog (in
this case black) and the other represents the color currently
selected above it. Move the cursor around the large palette and
you'll see the top square update. As you move the cursor around
and select colors, you might notice that a small triangle shows
up as you specify more saturated colors within the picker. This
indicates that the color selected is out-of-gamut based on the
currently selected CMYK profile loaded in the Color Settings. If
you click this triangle, the closest in-gamut colors are selected for
you. Try selecting some saturated colors by altering any of the
data fields or by clicking and dragging within the color palette
and see how this gamut warning and auto selection operates.
You may need to click one of the RGB radio buttons. In case you
are wondering about the smaller square box icon, it indicates if
the color is not web safe; clicking that would select the closest
colors that can be reproduced in the limited web-safe color
palette.
The best way to feel comfortable with the numeric scale of the various
color models is to plug numbers into one while viewing the updated
values on the other color models. In the end, you'll likely be working
with RGB values in well-behaved working space or CMYK values based
on a device profile. However, getting a better idea of how HSB and even
LAB behaves can be a worthwhile exercise. Click OK or Cancel when
finished inspecting the color picker.