4.1.2 Image Formats and Storage

The TIF and BMP Formats

	The TIF (Tagged Image Format) or BMP (bit map) formats are simple: Everything will be stored to the fullest amount.
			Every pixel is stored with the full information for brightness and 16 million colors
			It needs lots of memory space, is thus perfectly unsuitable for HTML, and cannot be incorporated directly
			It is, however, the format of choice to store your originals. You then optimize a copy of the original and store it in a compressed HTML compatible format.

The JPEG Format

	The JPEG format compresses the image data by using a discrete cosine transformation algorithm (similar to Fourier transforms etc.).
			The compression algorithm is rather good; it also keeps the maximum color information (i.e. a palette of 16.7 million colors). Most of the graphic programs offer the possibility of choosing the compression factor.
			With Paint Shop Pro you can choose the compression factor by activating the options in the "save as" ("Speichern als") menu.
			A high compression factor leads to small file with a very low quality and vice versa: A low compression factor will lead to a larger file with a very high quality. Just have a look at the examples in the link or at the test picture below.
			The JPEG format is a common format to present scanned photos or pictures with very fine color gradients in the www. JPEG offers no opportunity to declare a transparent background.

The GIF format

	The GIF format was developed by CompuServe especially for on-line use. GIF compresses the size of an image by reducing the palette to 256 colors. This reduces the bit size of an image to 1/10 to 1/30 compared to a regular BMP file without noticeable losses. The GIF format offers several options for including the image into a web page:
				Transparent background: One of the at most 256 colors of the image can be declared to be "transparent"; it will then be substituted by the background color of the page.
				Interlaced presentation: The image will be presented successively (layer by layer) while each layer shows more details
				Animations: Several GIF images can be connected to an animation; i.e. a short "comic strip".
	GIFs are best used for buttons, cliparts and other images with only a few colors or color shades, and particularly for drawings or texts presented as image, but not for high resolution photos.

The PNG format

	The PNG format (portable network graphics) combines the advantages of the JPEG and the GIF formats:
				Compression without noticeable losses
				16.7 million colors
				Transparent background and interlacing
	However, it does not allow to chose the compression factor

	Here is an example for the different ways of strong an image. It contains a photography, hard lines, many colors, and a continuous color transition. In the original TIF format it needs 152 kB
		Note that JPEG needs the least amount of storage space, but has problems with hard lines on a clear background. The photography, however, still looks pretty good even at high compression.
		You can see the differences more pronounced if you compare the images by exporting them to Paint Shop Pro and enlarging them.

	JPEG format with compression factor 1 ("Original") Storage Size is 58 kB.			JPEG format with compression factor 25 Storage Size is 15 kB.
	JPEG format with compression factor 50 Storage Size is 10 kB.			JPEG format with compression factor 75 Storage Size is 7 kB.
	GIF format. Storage Size is 43 kB			PNG format. Storage Size is 79 kB