Digital photography, which is also called ?digital imaging' since it does not involve the use of film started in the sixties. The original development of the technology is at NASA when they required that exploration spacecraft, unable to return to earth, to be capable of sending back pictures of their voyages.
The digital camera, like the standard film camera, uses a lens to focus the image on a sensor. The usual film camera depends on a film to capture the image but the digital relies on a sensor, either CCD or CMOS . As light hits the pixels that make up the sensor, it is converted to a current that is then sent to the ?Analogue to Digital Converter' or A-D converter.

When a photo is digitised, its colours are sampled from the sensor and converted to binary format. The smallest image element sampled is called a pixel. The digital image is like a map, where the information about the colour value of a pixel is understood as co-ordinates on the map. When the map is converted back to an image, the pixel goes to its position and colour in relation to the other pixels making up the image and the co-ordinates given to it.





This is how the camera maps out the image.







From the A-D converter, algorithms are then applied to the data converting it into a digital image. Sometimes, the size of the data generated by an image sensor can be very large. The larger the number of pixels making up the picture, the higher the resolution of the image and the larger the size of the data of the image. To deal with these large files, most digital cameras compress the data, as to make the size of the data of the image smaller. The way the data representing an image is electronically written is called an ?image file format'.

There are many different image file formats. Several of them use compression techniques to reduce the storage space required by the bitmap image data. These compression methods are classified in two ways: whether or not they remove detail and colour from the image. ?Lossless' methods compress image data without removing any detail from the image, while 'lossy' methods compress images by removing detail and colour depth. One of the more common standards of compression for digital cameras is the JPEG format.

The larger the image, and the more precise the sampling process, the larger the final digital file will be. To make the use of digitised photographs more utilised for transmission over Internet or for storing on a disk, algorithms have been constructed to decrease the size of data that is used in representing the image. When the process is reversed, the image is returns. Compression algorithms are useful when you need storage space, or to speed up data transmission on the Internet or anywhere. Without the JPEG format, the Internet would be much slower as this format is extensively used. To get large savings in the image files, many compression systems delete some of the information the file contains. The object is to make a compressed version of the image, so that once restored it is as close of a match to the original image as possible.



Many different algorithms have been developed to compress file sizes. Lossy compression is better than lossless because it can compress an image that can be as little as five percent of the original size. Lossy is where information from the image file is removed and lossless is just compressing the file.

The JPEG format was created specifically for the transmission and storage of photographic images. It is a lossy compression algorithm and it is made to remove different amounts of the data that originally made up the image. JPEG compression is designed to take advantage of a particular aspect of human visual perception: the fact that we perceive small colour changes less accurately than we perceive small changes in brightness.

The most important advantage coming from JPEG compression is the enormous reduction of file size. For digital cameras, this makes it possible to store a more images in the same amount of memory. JPEG compression makes it possible to send high quality images over the Internet, which would be never ever done using non-compression methods.