Graphics Programs Reference
In-Depth Information
test prints under controlled lighting until the final color appearance
desired was reproduced. Due to the inherent nature of color negatives,
they cannot be viewed directly. No original reference exists other than
the scene (and our memory of the scene) where the image was pho-
tographed. The color print represents the reproduction, or
color rendering
,
based upon how the photographer wished the print to represent the
scene. It is often impossible to absolutely match a transparency to a reflec-
tive print since the dynamic range of a transparency is usually much
greater. That didn't stop photographers and photo labs from making
prints from film, nor the clients' acceptance that they had received a
match from the original. It is worth noting that it is usually easier to
match two somewhat similar media such as a transparency to a print
compared to a print and an actual scene that we viewed originally with
our own eyes.
Digital Images Are Just Numbers
Enter computer imaging. It is important to understand that all a com-
puter understands are series of numbers: long strings of zeros or ones. It
is amazing that we can view what appears to be a full color image on our
computers when in fact all we are working with are numbers. It is impor-
tant to understand that color is a human perception, a sensation inside
our brains. All the colors displayed on a computer system are just numeric
values, and unfortunately, numbers don't tell us what a color looks like;
rather, they provide a partial numeric recipe for color. For this reason,
color management is vital when dealing with images on a computer.
Think of it this way: suppose I supply a recipe for chocolate chip cookies
but do not provide the unit for each ingredient in the recipe. The recipe
provides each ingredient followed by a number. Without units we can't
make the cookies. The numbers alone are not enough information to
describe the cookies that will be produced. Likewise, R78/G103/B23 is
not enough information to reproduce. Ultimately we need to see the
colors and know that these colors will be reproduced as we desire when
output (see Fig. 1-2).
The Pixel
Digital images displayed on a computer are composed of
pixels
(short
for “picture element”), the smallest building blocks of a digital file. Zoom
into a digital image as far as you can within Photoshop and you'll see
that the image is a mosaic of (usually) squares (pixels). Computers rep-
resent numeric values using the binary system, a method of counting
using only the digits 0 and 1. Each pixel has a numeric value associated
with it.
You may have heard of the term bit depth. The
bit depth
of a file refers
to the number of bits (places or columns) available to each pixel. Early
