File Type, Resolution, and Size

In this class we'll use a handful of file types for different kinds of images and documents. There are dozens and dozens of different formats in which a digital file could be saved, and each has a more or less unique purpose. Here are some of the more common types and why you might need them:

Bitmap
Bitmap images are direct or compressed 'maps' of a grid of pixels. Information about each pixel is saved to the file, so when it is loaded, the computer simply lays out each pixel onto the screen according to it's individual data. When compressed, a bitmap can be 'abbreviated' or cut to a smaller size - it takes shortcuts to fill in large areas of similar color using less data. Photoshop can be used to produce and edit Bitmap images.

.jpg (or JPEG, 'jaypeg')
The most common type of image file at the moment. JPEGs are compressed bitmap files, meaning they have been squished down to be smaller in terms of the amount of memory/disk space they take up on your computer. This is good because it allows for quicker downloading, easy storage, etc., but it also means the image can lose a lot of clarity depending on how much it is compressed. Each time a JPEG is saved, it is re-compressed and loses additional clarity, so you should never save a serious image file as a JPEG until it is ready to distribute.

.psd (Photoshop Document)
Photoshop's native file type. These tend to be large files because they are uncompressed, can contain layers, which we'll talk about today, and retain a lot of data about the image itself, including the history of all changes made to it. This is the file type you should use each time you begin working in Photoshop. When an image is finished, you can save it as another appropriate file type.

.gif ('Jiff' of 'Gif' - Graphics Interchange Format)
Another compressed bitmap file type that is common on the web. Gifs do not lose quality when repeatedly saved like JPEGs do, but they are limited to a maximum of 256 colors. Gifs can also be saved with multiple frames to enable animation. They also support transparency.

.png (Portable Network Graphics)
A newer compressed bitmap file that was designed to replace Gifs - they are better in many ways, including greater color depth, more advanced transparency, and sometimes smaller file size. Unlike Gifs, they do not support animation.

.tif (.tiff, TIFF - Tagged Image File Format)
A widely used print-media file type. It is generally uncompressed and can include some vector graphics -  this is typically used for final printing situations where the highest quality is needed. They are typically very large.

Vector 
We'll be getting into vector graphics next week. In short, they are unlike bitmaps in that they do not contain information about each pixel in an image. Instead, they are actually saved as sets of geometric equations, so to speak, that result in shapes, colors, and textures when read by the computer. This means they can be infinitely scaled up without losing clarity - the equations are just filled with larger values to blow them up bigger. This is useful for images that need to be printed, reproduced, or projected at different sizes without losing any clarity whatsoever.