Graphics file formats are standardized means of organizing and storing images in a file format.
Image file size[edit | edit source]
For some image formats, the size for storage of an image file is affected by the width and height of the image (image size), the number of possible colors that can be used (color depth) and the number of pixels in the image per section (resolution).
Image compression[edit | edit source]
It is just reasonable to compress images since large images tend to eat more storage space. Image compression algorithms are classified into lossy and lossless. Lossy algorithms retain a good quality of the original image, while sacrificing file size. An example of this is PNG. Lossless algorithms compress images well to a small size, but editing, resizing or further compressing the image will reduce the image's quality. An example is JPEG.
Raster and vector graphics[edit | edit source]
Raster graphics typically map data from the file to a fixed grid of pixels, where each pixel has its own representation in the file. Zooming in to the image would reveal the individual pixels in the image.
Vector graphics on the other hand uses geometric definitions that are also mapped to a grid. Unlike raster graphics, the lines, points, colors and all the other information are defined geometrically, so zooming in to the image would not reveal individual pixels.
Indexed color[edit | edit source]
In formats without indexed colors, individual pixels can have as many colors as the format's color depth would allow. With indexed colors, individual pixels are mapped to a specific color in a color table, and only those colors used will be available in the image. This may result in a better compression method, especially when only a few colors are used. An example of a format that supports indexed colors is GIF.
Transparency[edit | edit source]
Some images allow transparency, where users can "see through" the image. Some image formats support only opaque or transparent values, while others have an alpha channel, where the transparency can vary from 0 to 100%. Formats that support transparency include SVG, PNG and GIF.
Interlacing[edit | edit source]
Some images support interlacing, where data in the file is arranged such that it may be rendered in a way that while the file is being streamed, it is rendered on the fly from a low-quality version to a high-quality one.
Animation[edit | edit source]
Some images may also be animated. This is usually done by packaging multiple images into one. Supporting formats include SVG, GIF (most common) and APNG.