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Auteur

Michel DEGREMONT Elève-Ingénieur Supinfo Paris Promotion SUPINFO 2006    Lui écrire    Tous les projets de cet auteur    Le mini-CV de cet auteur

1. Raster image or Vectorial

1.1 Raster image

A Raster image or Bitmap is a collection of one or more pixels. Each pixel of the image can be controlled individually. What means that each pixel of image can be of a different color (color or shade).

For example a rectangle is a sequence of pixels. The Rather images require a high resolution.

1.2 Vectorial image

A vectorial image is a collection of one or more vectors. Mathematically, a vector is a combination magnitude and direction. In which one uses relations to represent relations between each points, lines, curves and forms full.

In an image, a vector is an entity which can be controlled. Each vector can separated by a color or a shade. Each vector can have various properties.

The vectors are mathematically described and can be shown with different sizes and resolutions without deteriorating the quality of the image. The image can be increased without loss of qualities or loss of data.

Ci below a very convincing example of a zoom on a pixellized image and an image vectorial.

Zoom image Raster	Zoom image vectorial

1.3 Format of the raster images

A pixelized image is a table of bits specifying the color of each pixel in a rectangle of the pixel.

The length and width of an image are measured in pixels. The number of bits by pixels specifies the number of color which one assigns with the pixel with the equation:

N C = 2 LP

N C = a number of colors which each pixel uses

LP = a number of bits per pixel

For example if Bp=8, then Nc = 2 8 = 256 colors.
and if LP = 24, then N C = 2 24 = 16,777,216 colors.

For an image of a bit per pixel we will have a monochromic image (for example black and white)

1.4 Graphic format

The possible formats of pixellized image are:

•  BMP
•  GIF
•  JPEG
•  EXIF
•  PNG
•  TIFF

1.4.1 BMP

BMP is a standard Windows format to store device-independent and application-independent bitmap images. The number of bits per pixel (1, 4, 8, 16, 24, 32, or 64) for a given BMP file is specified in a file header. BMP files with 24 bits per pixel are common.

1.4.2 GIF

Graphics Interchange Format ( GIF ) is a common format for images that appear on Web pages. GIF uses Lempel-Ziv-Welch (LZW) compression to minimize file size. No information is lost in the compression process; a decompressed image is exactly the same as the original. GIF files can use a maximum of 8 bits per pixel, so they are limited to 256 colors.

1.4.3 JPEG

Joint Photographic Experts Group ( JPEG ) is another popular format used on Web pages. JPEG can store 24 bits per pixel, so it is capable of displaying more than 16 million colors. Some information is lost during JPEG conversion, but it usually doesn't affect the perceived quality of the image. JPEG is not a file format; it is a compression scheme. JPEG File Interchange Format ( JFIF ) is a file format commonly used for storing and transferring images that have been compressed according to the JPEG scheme.

1.4.4 EXIF

Exchangeable Image File ( EXIF ) is a file format used by digital cameras. It was originally developed by the Japan Electronic Industry Development Association. The EXIF file contains an image compressed according to the JPEG specification. . You can read too this article for more information : Lecture des Métadonnées EXIF dans les images avec .Net

1.4.5 PNG

Portable Network Graphics ( PNG ) format provides the advantages of the GIF format but supports greater color depth. PNG files can store colors with 8, 24, 32, or 48 bits per pixel, and grayscales with 1, 2, 4, 8, or 16 bits per pixel. PNG also supports alpha channel, so it's a suitable format for storing images that support a high number of colors with transparency.

1.4.6 TIFF

Tag Image File Format ( TIFF or TIF ) can store images with arbitrary color depth, using a variety of compression algorithms. The TIFF format can be extended as needed by the approval and addition of new tags. This format is used by engineers when they need to add information in the image itself.

Almost all image file formats can also store metadata related to the image, such as scanner manufacturer, host computer, type of compression, orientation, samples per pixel, and so on.

invite you to read my article on Graphic Création in Php related to a data base which will indicate information complementary and bonds to you towards formats BMP, GIF, JPEG, png