Choosing the Correct Image formats

Whether you want to print your photos, show documents, publish on the
Internet, etc.., choose the correct format that corresponds to the use
you intend to do with your images.

JPEG, TIFF, PNG ... each format has its own characteristics. To choose
one that will match what you want to make your images, it is essential
to know.

First feature: color depth, expressed in bits, it is the number of
color values that can take each pixel in the image. JPEG, for example,
uses a color depth of 24 bits (or 8 bits per primary color: red, green,
blue), corresponding to more than 16.7 million tones for a pixel. Our
eyes are unable to discern all the nuances, and most printers can not
return them, this may seem sufficient.

Question of details

However, cameras and high-end scanners capture images with a color
depth of 12, 14, 16 bits or more per primary color, or billions of
colors. This saves additional information, useful when editing the
picture, to keep even the small details and to apply correction filters
with more precision and it offers greater flexibility than before the
'it would lead to a visible degradation of the image.

Another important criterion is compression. The lossless compression
possible with Tiff and PNG, for example, reduces a little the weight of
images without affecting their quality. On the other side, the JPEG
compression standard is called destructive: it eliminates image
information. Effective, but more compression, the higher the quality is
degraded.

What is Pixel?

It is the smallest meaningful element of a digital image. Each pixel is
a color, split into red, green and blue. The contrast of pixels, like a
mosaic, create an image (which can represent text). The pixel is used
as a measurement of the size of display screens. A pixel is not
necessarily square. Its shape depends on the support of display used,
its settings and technology.

Jpeg: the most universal

Joint Photographic Expert Group (JPEG) is a widely used format. JPEG
became a standard for photography as the publication of images on the
Internet (all browsers support it). Set in 1992, its a form of lossy
compression: it reduces the image by eliminating - irreversibly -
redundant information.

Each image software defines its own level of compression, for example
from 1 to 99 or 0 to 12, the lowest figure corresponding to the higher
compression. In this case, the file size can be divided by 50, but the
image is very degraded. Beware, each recording of an image causes a new
JPEG compression and thus further degradation. It is therefore
advisable to save an image in JPEG only after making any edits, and not
to manipulate it later.

• Compression: lossy
• Number of Colors : 16.7 million
• Number of grayscale : 256
• Management of transparency : no
• Conservation layers : no
• Uses: photos and illustrations, web publishing, printing

Gif: for animated images

Graphics Interchange Format (GIF), developed by CompuServe in 1987,
this format provides lossless compression and is suitable primarily for
Web images. It is capable of displaying 16.7 million tones, but can
save only 256 at the same time in an image. The GIF is not suitable for
photography. It is, however, very effective for images with few shades
of color (logos, graphics). The GIF also