Image Extension Types

There are two types of digital graphics files – vector and raster. Vector images are made of hundreds of thousands of tiny lines and curves (or paths) to create an image. Raster images are composed of pixels.

Vector images are rooted in mathematical theory. They are created in computer software that is designed to create this intricate wire-frame type image and each line includes defined node positions, node locations, line lengths and curves. Any of the lines and curves in the image can be assigned a color value. Because of this defined approach to drawing, each image can be sized and scaled repeatedly and limitlessly without losing resolution or pixelated. Text is one of the most common types of vector image, which always appear smooth even after increasing the font size. The most common problem with using vector images is compatibility. Vector images are often saved as native files from the program used to create the image, such as Adobe Illustrator.

Basic file types:

  • Adobe Illustrator: .ai, .ait, .art
  • Corel Draw: .cdr, .cdrw, .cdt
  • Corel: pat (Paint Shop Pro Pattern Image)
  • Digital Line Graph: .dlg, .do
  • OpenOffice: .odg

Raster images are often called bitmap images because they are made of millions of tiny squares, called pixels. One can identify a raster image by the square outlines of each pixel by zooming it enough. Raster graphics typically have larger file sizes than their vector counterparts. Higher DPI (dots per inch) and PPI (pixels per inch) settings also contribute to larger files. Raster images are the preferred method when working with photographs. When photos are taken with a digital camera or copied on a scanner, the resulting files are raster images. Almost all of the images on websites are raster images, even those that may have originally been created with paths. n printed mediums — such as books, magazines and newspapers — raster images are often used to reproduce photographs. Images are saved at a high DPI so that quality will not suffer during the printing process.

Basic file types:

  • Adobe Photoshop: .psd
  • .jpg
  • .gif
  • .png
  • .tiff or .tif

JPEG – It stands for Joint Photographic Experts Group. It is a group of experts that sets standards for computer images. Images produced using this standard are called JPEG ( pronounced Jay-Peg) images. JPG is the de facto standard image format and the most popular one used on the web. JPG supports 16.7 million colors and is the preferred format for photographs. JPG files are also smaller in size as compared to other image formats because it uses ‘lossy’ compression to reduce the file size. JPG images are ideal for rich color photographs, gradient images, and web images for their small size. It is not suitable for line drawings and animations. JPG also does not support transparency.

BMP – BMP stands for Bitmap image. The BMP format is a commonly used raster graphic format for saving image files. It was introduced on the Windows platform, but is now recognized by many programs on both Macs and PCs. The BMP format stores color data for each pixel in the image without any compression. For example, a 10×10 pixel BMP image will include color data for 100 pixels. This method of storing image information allows for crisp, high-quality graphics, but also produces large file sizes. The JPEG and GIF formats are also bitmaps, but use image compression algorithms that can significantly decrease their file size. For this reason, JPEG and GIF images are used on the Web, while BMP images are often used for printable images.

GIF – This stands for Graphics Interchange Format. GIF image has large areas with flat or single tones colors. Logos, icons, banners, and cartoons are all preferably GIF images. The GIF format supports 256 colors (i.e. an 8-bit color palette) which make images compact and consume less bandwidth. GIF is widely used in animation because it enables transparency and interlacing.

PNG – PNG stands for Portable Network Graphic Transparent file. It was also designed as an open patent free format usable by everybody, as against the proprietary GIF format. PNG handles transparency more efficiently than GIF. Like GIF, the PNG format supports 8-bit color but also extends it to 24-bits to provide more color ranges to work with. PNG files are also lossless files retaining color information when they are compressed. Richer images will lead to larger file sizes.

TIF or, TIFF – TIF stand for Tag Image File Format. TIFF  is a raster file format that is largely used in the publishing and printing industry. TIFF files are large and of very high quality.

RAW – A raw file is the image as seen by the camera\’s sensor. RAW files are used to produce higher quality images since the format stores data captured from a camera\’s sensor in an uncompressed format. RAW files do not lose data like JPEG files do when they are compressed. It contains uncompressed, raw image data that can be adjusted for exposure and white balance using software that supports the format.

PDF – Portable Document Format (PDF) is a file format used to present and exchange documents reliably, independent of software, hardware, or operating system. Invented by Adobe, PDF is now an open standard maintained by the International Organization for Standardization (ISO). PDF files are created from existing documents instead of from scratch.

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