When ever we take a picture of our dear ones and when we save them in our PC, we will be giving that image some name. Most of us surely wonder what that tail for the name we have given is. Well, those tails are called as Image file formats.

Image file formats are standardized means of organizing and storing digital images. Image files are composed of either pixel or vector (geometric) data that are rasterized to pixels when displayed (with few exceptions) in a vector graphic display. The pixels that constitute an image are ordered as a grid (columns and rows); each pixel consists of numbers representing magnitudes of brightness and color.

There are hundreds of image formats. But the most commonly used are PNG, JPEG, and GIF formats.

Before we learn about different types of formats, let’s see two important concepts. They are:

a)    Image file sizes and

b)    Image files compression.

IMAGE FILE SIZES:

Image file size is expressed as the number of bytes of the image. It increases with the number of pixels composing an image, and the color depth of the pixels. The greater the number of rows and columns, the greater the image resolution, and the larger the file.

IMAGE FILES COMPRESSION:

There are two types of image files compression algorithms: lossless and lossy.

Lossless compression algorithms reduce file size without losing image quality, though they are not compressed into as small a file as a lossy compression file. When image quality is valued above file size, lossless algorithms are typically chosen.

Lossy compression algorithms take advantage of the inherent limitations of the human eye and discard invisible information. Most lossy compression algorithms allow for variable quality levels (compression) and as these levels are increased, file size is reduced. At the highest compression levels, image deterioration becomes noticeable as “compression artifacting”.

Now coming to the detail information of file formats…

These graphic families are separated in to two different families. They are: Raster and Vector. And in some cases there will be another type of classification and that is mixture of both Raster and Vector which is called a Metafile.

RASTER FAMILY:

This format stores images as Bitmaps (pix maps)

1.    JPEG/JFIF:

JPEG or JPG is short form of Joint Photographic Experts Group and is a compression method. JPEG-compressed images are usually stored in the JFIF (JPEG File Interchange Format) file format. And JPEG compression is (in most cases) lossy compression. The JPEG/JFIF filename extension is JPG or JPEG. JPEG files suffer generational degradation when repeatedly edited and saved.

2.    JPEG 2000:

JPEG 2000 is a compression standard enabling both lossless and lossy storage. Compression methods used in this are different from above type. This format improves quality and compression ratios, but also requires more computational power to process.

3.  TIF:

TIFF is short form for Tagged Image File Format. This format is a flexible format that normally saves 8 bits or 16 bits per color (red, green, blue) for 24-bit and 48-bit totals, respectively. It has its file extension as TIFF or TIF. TIFFs can be lossy and lossless. Some offer relatively good lossless compression for bi-level (black & white) images.

4.    GIF:

GIF is short form of Graphics Interchange Format. It is limited to an 8-bit palette, or 256 colors. This makes the GIF format suitable for storing graphics with relatively few colors such as simple diagrams, shapes, logos and cartoon style images. The GIF format supports animation and is still widely used to provide image animation effects. It also uses a lossless compression that is more effective when large areas have a single color, and ineffective for detailed images.5.    PNG:

The PNG (Portable Network Graphics) file format was created as the free, open-source successor to the GIF. The PNG file format supports true color (16 million colors) while the GIF supports only 256 colors. The lossless PNG format is best suited for editing pictures, and the lossy formats, like JPG, are best for the final distribution of photographic images, because in this case JPG files are usually smaller than PNG files. PNG is designed to work well in online viewing applications like web browsers so it is fully usable with a progressive display option.

Above is a .png file which is mainly used in websites where true colors are needed.

6. BMP:

The BMP file format (Windows bitmap) handles graphics files within the Microsoft Windows OS. Typically, BMP files are uncompressed, hence they are large.

Other image file formats of raster type include:

A)   JPEG XR (New JPEG standard based on Microsoft HD Photo)

B)   PCX (Personal Computer exchange)

C)   PSD (Adobe Photo Shop Document)

D)  FITS (Flexible Image Transport System)

E)   PSP (Corel Paint Shop Pro)

AND SO ON…

VECTOR FORMATS:

As opposed to the raster image formats above, vector image formats contain a geometric description which can be rendered smoothly at any desired display size. At some point, all vector graphics must be rasterized in order to be displayed on digital monitors. However, vector images can be displayed with analog CRT technology such as that used in some electronic test equipment, medical monitors, radar displays, laser shows and early video games. Plotters are printers that use vector data rather than pixel data to draw graphics.

  1. CGM:

CGM (Computer Graphics Metafile) is a file format for 2D vector graphics, text and is defined by ISO/IEC 8632. CGM provides a means of graphics data interchange for computer representation of 2D graphical information independent from any particular application, system, platform, or device. It has been adapted to some extent in the areas of technical illustration and professional design.

  1. SVG:

SVG (Scalable Vector Graphics) is an open standard created and developed by the World Wide Web Consortium to address the need for a versatile, scriptable and all-purpose vector format for the web and otherwise. The SVG format does not have a compression scheme of its own, but due to the textual nature of XML, an SVG graphic can be compressed using a program such as GZIP. Because of its scripting potential, SVG is a key component in web applications: interactive web pages that look and act like applications.

Some of the other types in this family are

a)    Asymptote

b)    AL (adobe illustrator)

c)    Graphics Layout Engine

d)    MathMl

e)    HPGL (printer language)

f)    SWF(shock wave flash)

g)    PDF(portable document format)

And so on…

courtesy: howstuffworks and wikipedia

Posted by

Gopi Chand ( MGIT ECE 3rd year)

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