on 1/13/01 1:24 PM, John Woodworth at [EMAIL PROTECTED] wrote:
> I don't see how the number of bits has much to do with the gamut.
It doesn't.
> The
> number of bits will determine the number of shades possible between the
> darkest and the brightest but not the range (which is the gamut).
The number of bits doesn't even have to do with the shades possible. You've
got to have 1000 shades first and then the added bit depth can be useful.
But you can have a high bit file with a lot fewer shades and a 24 bit file
with more shades. The math leads many to believe that more bits means more
shades. In theory you can have more shades and divide them up finer with
more bits but you have to actually have the shades to begin with. A 48 bit
file of a black wall doesn't have as many shades as a 24 bit file of a
continuous tone scene.
> So, the gamut for a green box of crayons refers to the range between the
> darkest and the brightest green crayon.
Colorspaces are three dimensional. Visualize a globe, much like our earth.
>From the center of the globe to the outer edge to the equator is one axis
that can describe brightness (let's say the center is as black as black can
be, zero), the edge is as white as white can be (255). The circumference is
the hue (360 degrees) of color (good old Roy G Biv). From the center to one
pole is saturation (from zero saturation or neutral to the most saturated
color that can be produced in this colorspace). In a way, you can think of
the gamut as the range from neutral to fully saturated a color can be but of
course we have the circumference to contend with too. Some areas of hue may
have a wider saturation than others. When you look at a plot of a devices
gamut, you are looking at two of the three possible dimensions. Some
products allow one to load an ICC profile and rotate the gamut 3
dimensionally and that's really helpful for evaluating the color gamut and
getting a better idea of the colorspace.
The gamut of the green part of our box of crayons gives us an idea of how
saturated a green we are able to produce. Go into Photoshop and pick 255G 0B
0R and you'll see a little exclamation which indicates that this color is
out of gamut for whatever CMYK profile you happen to have loaded. Doesn't
matter, you'll never be able to output 255G 0B 0R in CMYK. If you click on
the green square under this exclamation which looks more muted, Photoshop
will select the closest green within gamut for this CMYK model. So what you
are seeing is that this is the greenest green you could produce to this
device. The original green is way out of gamut. Try loading other CMYK
profiles and the green that is picked within gamut will change (some more
green some less green i.e. Closer or farther from your original goal of
255G).
Andrew Rodney
