Image+Type

=Digital Image File Types Explained= **Resolution**: Refers to the sharpness and clarity of an image, measured in terms of ppi and dpi.

Resolution Truths
Raster based software tools are used for continuous tone images such as photos and paintings. Raster, or pixel based images can have millions of colors and a variety of levels of pixels per inch of image. In display output settings such as for the web, the standard resolution is 96 pixels per inch. This is an example of a pixel based image. Could you imagine describing all of the colors of this woman's face? There are many colors and to display this accurately the pixels have to display each one of them right next to each other.
 * Every pixel-based image, called a raster image, is made of squares of color.
 * PhotoShop images are raster images.
 * Stretching a raster image creates distortion.
 * Never stretch a raster image. -- If it is too small, get another one!

Bit-mapped (or **Raster**) images: Images that have data that describe the color of each pixel. Larger display sizes equal larger file sizes in this type of image. Bitmapped images cannot be rescaled without resulting in "pixilation", or loss of definition in the details. JPEG and GIF images are examples of bitmapped images.
 * Computer display**: Images intended primarily for display on a computer monitor (such as email attachments or images on a Web page) really only need a 72ppi to 96ppi resolution, as that is what computer monitors are capable of displaying. A higher resolution will not make your image appear any better on the screen. In fact, if you don't expect folks to print out your images, these images should be "optimized", which means making them as small and compressed a file as possible (while still retaining the appropriate visual clarity), so that they load quickly, and do not take up too much space on the hard drive.
 * PPI**: (pixels per inch) Measurement used for images displayed on screen.
 * Pixel**: A word invented from "picture element" - the basic unit of programmable color on.
 * RGB**: (Red, Green, Blue) The color model for display devices (monitors, digital projectors, etc.) Each displayed color is determined by a combination of RGB.

Lossy vs. Lossless compression
You will often hear the terms "lossy" and "lossless" compression. A **lossless** compression algorithm discards no information. It looks for more efficient ways to represent an image, while making no compromises in accuracy. In contrast, **lossy** algorithms accept some degradation in the image in order to achieve smaller file size. A lossless algorithm might, for example, look for a recurring pattern in the file, and replace each occurrence with a short abbreviation, thereby cutting the file size. In contrast, a lossy algorithm might store color information at a lower resolution than the image itself, since the eye is not so sensitive to changes in color of a small distance.

Explanation of File Formats
It is also helpful to understand the common image file formats of digital images, how these file formats differ, and what their recommended use is. TIFF (.tif), JPG (.jpg, .jpeg), GIF (.gif) and PNG (.png) are file formats (and their respective file extensions) that you are likely to encounter. Other image file formats are used to a lesser extent; these formats are often proprietary, such as Photoshop .psd files.
 * **TIFF** || A lossless file format that can be compressed. This format is widely supported across operating systems. TIFF is the best file format for archiving high quality images. ||
 * **JPG or JPEG** || The JPG file format was specifically created for photographs, and can contain millions of colors. JPGs are automatically compressed (you can choose the level of compression to match your desired image quality), resulting in a relatively small file size while still retaining quality. For this reason, JPGs are ideal for email and Web use. JPGs are lossy, discarding information each time that they are compressed. ||
 * **GIF** || The lossless and compressed file format that is preferred for graphics, because it keeps edges and lines sharp. GIFs are limited to 256 or fewer colors, and are not recommended for photographs, but rather for images with flat fields of color, such as clip art. GIFs can be static or animated. ||
 * **PNG** || Portable Network Graphics format, an open source substitute for GIFs. PNGs provide a higher lossless compression rate than GIFs, and help to reduce cross-platform differences in image display quality, among other technical advantages. PNG provides a useful format for the storage of images during intermediate stages of editing. ||