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are at risk over time since companies come and go and interest waxes and
wanes. One solution to this growing problem is a new Adobe format called
the Digital Negative (.DNG). This publicly defined and openly shared format
for RAW files is an attempt to ensure that you will be able to access your
image files in the future. If your camera doesn’t capture RAW images in this
format, you can convert them to DNG using a program such as Photoshop or
Lightroom. When you do so, you can even choose to store the original RAW
image inside its DNG file so you can extract it at some future date should you
need it. The DNG format is supported by Photoshop and other Adobe prod-
ucts, some other software companies, and a number of camera companies. As
with all things in computing, only time will tell if the format becomes widely
accepted or gradually fades away.- TIFF (tagged image file format) is a format that’s often used to exchange
files between applications and computer platforms. It’s supported by virtually
all paint, image-editing, and page-layout applications. TIFF files tend to be
larger than both JPEG and RAW images and can be saved using either 8 bits
or 16 bits per color.
File ComPreSSion
Image files are huge compared to many other types of computer files. For
example, files captured by a 12 Megapixel camera can range up to 18 Mega-
bytes. As resolutions continue to increase, so will file sizes. To make image
files smaller and more manageable, digital cameras use a process called com-
pression. During compression, data that is duplicated or that has little value
is eliminated or saved in a shorter form, to reduce a file’s size. For example, if
large areas of the sky are the same shade of blue, only the value for one pixel
needs to be saved along with the locations of the other pixels with the same
color. When the image is then opened and displayed by any application, the
compression process is reversed more or less depending on which form of
compression was used—lossless or lossy.- Lossless compression compresses an image so when it is uncompressed,
as it is when you open it, its image quality matches the original source—noth-
ing is lost. Although lossless compression sounds ideal, it doesn’t provide
much compression so files remain quite large. For this reason, lossless com-
pression is only used by the highest quality image formats—namely TIFF and
RAW. - Lossy compression (rhymes with “bossy”) can dramatically reduce file
sizes. However, this process degrades images to some degree and the more
they’re compressed, the more degraded they become. In many situations,
such as posting images on the Web or making small to medium sized prints,
the image degradation isn’t obvious. However, if you enlarge an image
enough, it will show. The most common lossy file format is JPEG and many
cameras let you specify how much they are compressed. For example, many
cameras let you choose Fine (1:4), Normal (1:8), and Basic (1:16) compres-
sion. This is a useful feature because there is a trade-off between compression
and image quality. Less compression gives you better images so you can make
larger prints, but you can’t store as many images.
rGB Color
When you view a natural scene you are able to distinguish millions of colors.
A digital image can approximate this color realism, but how well it does so
depends on your camera and the settings you choose. The number of colorsClick to see the effects
of compression.The almost universally
recognized icon for
image quality.Here, two versions of
the same image. The
image on top is the
original JPEG. The one
on the bottom shows
what happens after
it’s saved a few times
at the lowest quality
setting. Art courtesy of
webweaver.nu.imAge FormAtsThe DNG logo.