There are so many image/graphic formats available in the modern day but only few of them are widely used depending on user’s need.Mostly used formats are PNG, GIF and JPEG. Before talking about image formats, it is necessary to have an idea about color depths. There are color depths(palettes) with Indexed color and Direct color.
Index color – it means image can store only limited number of colors(usually 256) which are defined by the author.
Direct color – which means image can store many thousands of colors that have not been chosen by the user.
Image File formats
BMP – Bitmap Image (Lossless / Indexed and Direct)
This is an old image format and it is loseless which means no image data is lost on saving, but compression at all. Therefore saving an image as BMP will result a large file size. Good thing about this format is, it can have both index and direct color palettes. But because of large file size nobody really uses this format commonly.
Usage: Nothing really, though BMP can excel anything better than other formats.
GIF - Graphics Interchange Format (Lossless / Indexed only)
GIF uses loseless images compression, thus the details of the image do get lost when it save over and over again. In GIF, file size is comparatively lower than BMP, though both of them use loseless compression. Because GIF uses a good loseless compression method. But it can only store 256 colors(indexed), it sounds small when it comes to digital photography.
GIFs can be animated and can have transparency.
Usage: Logos, line drawings, and other simple images that need to be small. Mainly used for websites.
JPEG - Joint Photographic Experts Group (Lossy / Direct)
JPEG images were designed to make detailed photographic images while keeping file size small as removing image details which are not noticing to the human eye. Therefore JPEG is a lossy format – image data gets lost or disappear when save it over and over again. It can store thousands of colors, which means suitable for photography but because of lossy format, it is not good for logos & line drawings . It looks fuzzy and takes a larger file size than GIF.
Usage: Photographs & gradients.
PNG-8 - Portable Network Graphics (Lossless / Indexed)
PNG is a newer format, and PNG-8 (the indexed version of PNG) is really a good replacement for GIFs. However, there are a few drawbacks: Firstly it cannot support animation like GIF can ( it can, but only Firefox seems to support it, unlike GIF animation which is supported by every browser). Secondly it has some support issues with older browsers like IE6. Thirdly, important software like Photoshop have very poor implementation of the format. PNG-8 can only store 256 colours, like GIFs.
Usage: Replaces GIF with having support for Alpha Transparency.
PNG-24 – (Lossless / Direct)
PNG-24 is a great format that combines lossless encoding with Direct color (thousands of colours, just like JPEG). It’s very much like BMP in that regard, except that PNG actually compresses images, so it results in much smaller files. Unfortunately PNG-24 files will still be much bigger than JPEGs, GIFs and PNG-8s.
Even though PNG-24s allow thousands of colours while having compression, they are not intended to replace JPEG images. A photograph saved as a PNG-24 will likely be at least 5 times larger than a equivalent JPEG image, which very little improvement in visible quality.
Just like PNG-8, PNG-24 supports alpha-transparency, too.
SVG - Scalable Vector Graphics
SVG is an XML-based vector image format for two-dimensional graphics that has support for interactivity and animation. The SVG specification is an open standard developed by the World Wide Web Consortium (W3C) since 1999.
SVG images and their behaviors are defined in XML text files. This means that they can be searched, indexed, scripted, and, if need be,compressed. As XML files, SVG images can be created and edited with any text editor, but it is often more convenient to create them with drawing programs such as Inkscape.