Graphics Programs Reference
In-Depth Information
FIGURe 3.26
Histogram
showing redistribution across tonal
range and consequent detail loss
In Chapter 12, “Developing Photos,” you will learn nondestructive workflows
in which you will apply color corrections, make multiple tonal adjustments,
reduce noise, and sharpen all at once through the Adobe Camera Raw interface.
Compressing data
Although a set number of pixels consume a given amount of RAM, it is pos-
sible to compress the data so the file takes up less storage space. For example,
the
Cabin.jpg
sample file you opened earlier in this chapter is a 21-megapixel
image, which consumes 60.2 MB of RAM. However, as a JPG file, the size on the
hard drive is only 6.1 MB (showing almost tenfold compression).
Compression works in principle by efficiently representing patterns in the
data. For example, if there were a million 1s in a row, it would be more effi-
cient to state that fact rather than literally listing one million 1s in the file.
Compression schemes are obviously more technical than this, but you get the
general idea.
There are two types of compression: lossless and lossy. Lossless compression
represents data concisely and without error but doesn't compress the data as
much as lossy methods do. Tagged image file format (TIFF) files support loss-
less compression schemes and are good for printing because they don't sacrifice
any detail.
Lossy compression sacrifices some of the detail for the sake of smaller file
sizes. The Joint Photographic Experts Group (JPEG) format is widely used on
the Web because of the small file sizes made possible with lossy compression.
Figure 3.27 compares lossless versus lossy compression in terms of quality. You
can plainly see JPEG
artifacts
in the lower image due to the extreme level of
lossy compression used.
