Graphic File Format Comparisons

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--- Graphic File Format Comparisons ---

File Type Comparisons

Note: Not all graphics will appear in all browsers (specifically Bitmap and Portable Network Graphics)

Graphic file format information...

There are numerous file formats for graphics.

Bitmap is a popular format for capturing and displaying computer images. All of the information is stored as a series of pixels (by height and width) with each pixel ranging in color depth from 2 to millions of colors.

Bitmaps are not compressed, therefore, they maintain the highest image quality.

Color depth

	A single bit can be used to represent two colors
	4 bits=16 colors
	8 bits (1 byte)=256 colors
	16 bits (2 bytes) = 65,536 colors (high color)
	24 bits (3 bytes) = 16+million colors (true color)

JPEG and GIF are popular file formats for web-based graphics--they both enable compression of graphic images.

GIF (Graphics Interchange Format)...

	Considered a lossless compression (it uses a technique of grouping same color pixels to minimize file storage).
	It is limited to 256 colors
	Uses LZW compression, a proprietary format owned by Sperry
	Includes transparent and animated capabilities

JPEG (Joint Photographic Experts Group)

	Is a lossy compression format (pixels are averaged).
	24 bit color
	Variable compression feature
	Compression algorithm is in the public domain.

PNG (Portable Network Graphics)...

	An emerging file format developed by Microsoft as a replacement for GIF.
	Up to 24 bit color
	Not supported by all browsers.

Photograph - JPG is the best format for web delivery

Bitmap BMP - 16 million colors - 200 X 151 pixels (89 KB)

Bitmaps are uncompressed representations of images. The image is made up of pixels, each pixel ranges from 2 to over 16 million colors. The color for each pixel is stored in bits and bytes (remember 8 bits = 1 byte). For example:

File size depends on the color depth (typically 2, 16, 256, 64,000, and 16 million colors) and the size of the image. For example:

	Full screen (640 X 480 pixels - VGA) image at 256 colors requires about 310,000 bytes.
	A full color image (16 million colors) would require over 900,000 bytes.

Portable Network Graphics PNG (29 KB)

PNG is a newer format released by Microsoft as a potential replacement for GIF. PNG graphics range up to 24 bit (16 million) color images.

JPG - 16 million colors (6 KB)

JPG files are based on 24 bit color. They are optimized for photographic images or graphics with a great deal of color to create smooth surface appearances (e.g., skin color).

GIF - limited to 256 colors (20 KB)

GIF is technically a proprietary format requiring a license agreement to use the LZW compression algorithm. GIF is limited to 256 colors.

Drawn Image - GIF is best for web delivery

Bitmap BMP - 16 Million colors - 316 X 201 pixels (187 KB)

PNG (4 KB)

JPG (10 KB)

GIF (5 KB)

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