Image File Formats

• There are different 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.

Image file sizes:-

• the raster image files is correlated with resolution,image sizes(number of pixels) and the color depth(bits per pixel).
• A compression algorithm stores either an exact representation or an approximation of the original image in a smaller number of bytes that can be expanded back to its uncompressed form with a corresponding decompression algorithm.
For example:A 640*480 pixel image with 24-bit color would occupy almost a megabyte of space 640*480*24 = 7,372,800 bits = 921,600 bytes = 900 KiB.

Image file compression:-

There are two types of images file compression algorithms:
1.lossless compression :algorithms reduce file size while preserving a perfect copy of the original uncompressed image.
• loseless compression generally, but not always, results in larger files than lossy compression.
• loseless compression should be used to avoid accumulating stages of re-compression when editing images.
2.Lossy compression : algorithms preserve a representation of the original uncompressed image that may appear to be a perfect copy, but it is not a perfect copy.often lossy compression is able to achieve smaller file sizes than lossless compression algorithm allow for variable compression that trades image quality for the size.
• There are hundreds of image file types.
the PNG,JPEG and GIF are most often used to display images on the internet.
Graphic formats are listed and briefly described below, separated into the two main families of graphics: raster and vector

Raster formats:-




JPEG(Joint Photographic Experts Group)
• Is a lossy compression method.
• JPEG-compressed images are usually stored in the JFIF(JPEG File Interchange format) file format.
• 24 bit color, with up to 16 million colors.


BMP(Bitmap)

• the windows Bitmap or Bmp files are image files within the Microsoft windows operating system.In fact,it was at one point one of the few image formats.
• These files are large and uncompressed, but the images are rich in color, high in quality, simple and compatible in all windows os and programs.
• BMP files are made of millions and millions of dots called 'pixels', with different colors and arrangements to come up with an image or pattern.


GIF(Graphics Interchange Format)

• GIF is limited to the 8 bit palette with only 256 colors.
• GIF is still a popular image format on the internet because image size is relatively small compared to other image compression types.
• GIF is lossless for images with 256 colors.
• One edge of the GIF Image format is the Interlacing Feature,giving the illusion of fast loading graphics.


PNG(Portable Network Graphics)

• It is created as a free, open-source alternative to GIF.
• The PNG file format supports eight-bit paletted image and 24-bit true color or 48-bit true color with and without alpha channel-while GIF supports 256 colors and a single transparent color.
• Lossless, so it does not lose quality and detail after image compression.
• In a lot ways better then GIF.To start PNG often creates smaller files sizes than GIF.


TIFF(Tagged Image File Format)

• The TIFF format is a flexible format that normally saves eight bits or sixteen bits per color for 24-bit and 48-bit totals.
• The structure was designed to be easily extendable, TIFF can be lossy or loseless, depending on the technique chosen for storing the pixel data.
• TIFF image format is not widely supported web browsers.
• Tiff remains widely accepted as a photograph file standard in the printing business.

Notes