Image Formats

Image file formats are standardised means of organising and storing digital images. Image files are composed of digital data in one of these formats that can be rasterised for use on a computer display or printer. An image file format may store data in uncompressed, compressed, or vector formats. Once rasterised, an image becomes a grid of pixels, each of which has a number of bits to designate its colour equal to the colour depth of the device displaying it.

Here are the most common image formats:

JPEG:

JPEG is short for Joint Photographic Experts Group, and is the most popular among the image formats used on the web. JPEG files are very ‘lossy’, meaning so much information is lost from the original image when you save it in JPEG file. This is because JPEG discards most of the information to keep the image file size small; which means some degree of quality is also lost.

Pros of JPEG:

·       24-bit colour, with up to 16 million colours

·       Rich colours, great for photographs that needs fine attention to colour detail

·       Most used and most widely accepted image format

·       Compatible in most OS (Mac, PC, Linux)

Cons of JPEG:

·       They tend to discard a lot of data

·       After compression, JPEG tends to create artifacts

·       Cannot be animated

·       Does not support transparency

 A JPEG format image

GIF:

GIF, short for Graphics Interchange Format, is limited to the 8 bit palette with only 256 colours. GIF is still a popular image format on the internet because image size is relatively small compared to other image compression types.

GIF compresses images in two ways: first, by reducing the number of colours in rich colour images, thus reducing the number of bits per pixel. Second, GIF replaces multiple occurring patterns (large patterns) into one. So instead of storing five kinds of blue, it stores only one blue.

Compared to JPEG, it is lossless and thus more effective with compressing images with a single colour, but pales in detailed or dithered pictures. In other words, GIF is lossless for images with 256 colours and below. So for a full colour image, it may lose up to 99.998% of its colours.

Pros of GIF:

·       Can support transparency

·       Can do small animation effects

·       ‘Lossless’ quality–they contain the same amount of quality as the original, except of course it now only has 256 colours

·       Great for images with limited colours, or with flat regions of colour

Cons of GIF:

·       Only supports 256 colours

·       It’s the oldest format in the web, having existed since 1989. It hasn’t been updated since, and sometimes, the file size is larger than PNG.

A GIF format image

BMP:

The Windows Bitmap or BMP files are image files within the Microsoft Windows operating system. In fact, it was at one point one of the few image formats. These files are large and uncompressed, but the images are rich in colour, high in quality, simple and compatible in all Windows OS and programs. BMP files are also called raster or paint images.

BMP files are made of millions and millions of dots called ‘pixels’, with different colors and arrangements to come up with an image or pattern. It might an 8-bit, 16-bit or 24-bit image. Thus when you make a BMP image larger or smaller, you are making the individual pixels larger, and thus making the shapes look fuzzy and jagged.

BMP files are not great and not very popular. Being oversized, bitmap files are not what you call ‘web friendly’, nor are they compatible in all platforms and they do not scale well.

Pros of BMP:

·       Works well with most Windows programs and OS, you can use it as a Windows wallpaper

Cons of BMP:

·       Does not scale or compress well

·       Again, very huge image files making it not web friendly

·       No real advantage over other image formats

A BMP format image

TIFF:

TIFF was created by Aldus for ‘desktop publishing’, and by 2009 it was transferred to the control of Adobe Systems. TIFF is popular among common users, but has gained recognition in the graphic design, publishing and photography industry. It is also popular among Apple users.

The TIFF image format is easy to use with software that deals with page layout, publishing and photo manipulation via fax, scanning, word processing, etc. TIFF is very flexible, it can be lossy or lossless. TIFF is a rich format and supported by many imaging programs. It is capable of recording halftone image data with different pixel intensities, thus is the perfect format for graphic storage, processing and printing. This makes TIFF the superior raster image format.

Pros of TIFF:

·       Very flexible format, it supports several types of compression like JPEG, LZW, ZIP or no compression at all.

·       High quality image format, all color and data information are stored

·       TIFF format can now be saved with layers

Cons of TIFF:

·       Very large file size–long transfer time, huge disk space consumption, and slow loading time.

A TIFF format image

PNG:

PNG or (Portable Network Graphics) is a recently introduced format, so not everyone familiar with it. But PNG has been approved as a standard since 1996. It is an image format specifically designed for the web. PNG is, in all aspects, the superior version of the GIF. Just like the GIF format, the PNG is saved with 256 colours maximum but it saves the colour information more efficiently. It also supports an 8-bit transparency.

Pros of PNG:

·       Lossless, so it does not lose quality and detail after image compression

·       In a lot way better then GIF. To start, PNG often creates smaller file sizes than GIF

·       Supports transparency better than GIF

Cons of PNG:

·       Not good for large images because they tend to generate a very large file, sometimes creating larger files than JPEG.

·       Unlike GIF however, it cannot be animated.

·       Not all web browsers can support PNG.

 A PNG format image

Comparison of different types of image formats