What are Raster Images and What are Their File Formats?

Raster files

Rasterized, or bitmapped, files are everywhere you look in graphics, whether you realize it or not. Essentially a fancy word for a photograph in its digital form, bitmaps break images down into an extensive grid of individually colored pixels. Higher resolutions mean more pixels for every square inch of space (Pixels Per Inch PPI), and therefore look smoother, and give you more options as far as scaling and manipulation. Raster images have a set amount of pixels (original PPI), when scaled up,  grey pixels are added between real pixels causing the image to look more jagged, blurry, and what is call pixilated. There is a point of scaling too far where the image should not be used. To examine if your file is too pixilated when at your final prints size zoom in to your image 100% and see how it looks. If it looks separated and blurry the image may be too low res for that size.

Here are the most common raster formats you should be familiar with:
  1. PSD– (PhotoShop Document) A PSD is the default file type used by Adobe Photoshop, one of the most widely used photo-editing programs. It is meant to contain all project-related information so that one can return to a document with all layers and editing intact for revisions.
  2. JPEG (Joint Photographics Expert Group) The most widely used image file type, supported by most cameras, computer platforms, and applications. Its compression scheme reduces the file size, making it perfect for sending through email or posting online. JPEGs are “lossy,” which means the type of compression utilized discards unnecessary information, making for a very compact image. However, one must be careful when saving in this format, because too much compression, or repeatedly saving, creates what are called “artifacts,” or degradation of image quality.
  3. PNG (Portable Network Graphic) is perfect for transferring images online without losing data. It also allows you to save transparency, (unlike JPEG) which lets you create “cut-out” images. This format is widely supported on modern web browsers such as Mozilla Firefox, and is quickly becoming a replacement for GIFs. When taking screenshots most computers will automatically save them as PNG files.
  4. TIFF (Tagged Image File Format) is used to exchange file formats between applications and platforms. Because of the many variations possible, it is not as widely accepted as other types of bitmaps, however it allows for the highest possible photographic quality in final output, and is often used by printers.  If chosen with no compression this file holds all information including layers.
  5. BMP (Bitmap) was originally created for Microsoft (though not exclusively used by PCs) graphics files. These files are easily read by all programs due to being uncompressed, but this generally translates into a very large file size.
  6. GIF (Graphics Interchange Format) is a lossless form of compression and is great for storing graphics like diagrams and logos. These, along with PNGs make up the most useful file types for online applications. GIFs are unique in that they can contain motion, and are often seen online in quick, looped animations.

If you have further questions on the file formats for raster files please feel free to contact us at connect@duggal.com 🙂