Image file formats allow the organising and storing of digital images to be standardised. Files are made up of pixels and/or vector data. Ultimately whichever format is used the files are rasterised to pixels when displayed.
A bitmap is a dot matrix data structure normally a rectangular grid of pixels which can viewed on screen and printed on paper.
Image files can be compressed or uncompressed. Lossless compresssion reduces the file size without any degradation of the image quality. Lossy compression uses the limitations of the human eye to remove invisible information. It allows variable compression levels and as these increase the file size is reduced. Image degradation can occur at high compression level and this is referred to as pixelation.
Six predominant image file formats were detailed during the lecture. These being
PSD, Adobe photoshop file format, is uncompressed and lossless. TIFF, which stands for Tagged Image File Format, is widely used by graphic artists and photographers. It can be both compressed and uncompressed, lossy and lossless. DNG (digital negative) is based on the TIFF format, it has an open lossless RAW format, and was written by Adobe. Widely used by digital photographers, and because it contains metadata it is a popular format for archivists. GIF (graphic interchange format) was developed by CompuServe in the late 1980’s. It allows animation and it’s lack of colour depth can provide the image with an interesting quality. PNG (portable network graphics) uses lossless compression. It was developed as an improvement to GIF. JPEG (joint photographers expert group)uses lossy compression and allows the production of very small files which can be used for sharing via email and online display.