Sofia Pasarin
Image file formats
1) What is meant by Image file formats?
Image file formats are standardized means of organizing and storing digital images.
Image files are composed of digital data in one of these formats that can be rasterized for
use on a computer display or printer. An image file format may store data in
uncompressed, compressed, or vector formats. Once rasterized, an image becomes a grid
of pixels, each of which has a number of bits to designate its color equal to the color depth
of the device displaying it.
2) Which are the ways that images formats can be stored?
The most important ones are GIF, JPG and TIF. Other examples are PNG, RAW, BMP and
PSD.
3) Define the unit of an image.
It is the format with which the image has been saved: the pixel.
4) How are images compressed?
You will often hear the terms "lossy" and "lossless" compression. A lossless compression
algorithm discards no information. It looks for more efficient ways to represent an image,
while making no compromises in accuracy. In contrast, lossy algorithms accept some
degradation in the image in order to achieve smaller file size.
A lossless algorithm might, for example, look for a recurring pattern in the file, and replace
each occurrence with a short abbreviation, thereby cutting the file size. In contrast, a lossy
algorithm might store color information at a lower resolution than the image itself, since
the eye is not so sensitive to changes in color of a small distance.
5) Why are images compressed?
Part of the reason for the plethora of file types is the need for compression. Image files
can be quite large, and larger file types mean more disk usage and slower downloads.
Compression is a term used to describe ways of cutting the size of the file. Compression
schemes can by lossy or lossless.
Another reason for the many file types is that images differ in the number of colors
theycontain. If an image has few colors, a file type can be designed to exploit this as a way
of reducing file size.
Sofia Pasarin
6) Define a metafile
A metafile can refer to two different types of computer files. The first is a file that
describes the contents of other files. This type of metafile may contain metadata, which
defines a group other files and gives a summary of what data they contain.
The second type of metafile is most often used in computer graphics. These files define
objects and images using a list of coordinates. They are typically used for vector images,
such as Adobe Illustrator, CorelDRAW, and EPS files, but can include raster images as well.
Fill this table:
File
type
Maximun
colors
Metadata
(yesNo)
JPG
Bits used
to
combine
24
256
Yes
TIF
24-48
256-65536
Yes
PNG
24-48
256-65536
Yes
Benefits
Drawbacks
Photo example
Sofia Pasarin
GIF
BMP
1-8
256
Yes
Yes