DIGITAL CAMERAS-Image Compression & File Formats
The photo taken by a digital camera is huge as compared to the normal images you get on your average PC or website. The usual image on your PC is 640 x 480 which usually takes about 1 megabyte of memory. A high resolution 1024 x 768 image can take as much as 2.5 megabytes. As the resolution and image size increases so does the memory requirement of the image. With storage capacity limited, some sort of compression is required. To reduce the size of image files and make them more economical, every digital camera uses some form of compression. Compressing images not only makes it possible to save more images on the camera's storage device; it also reduces download and display time.
During compression, any data that is identical or data that has no value is either eliminated or saved in a shorter format. This greatly reduces the size of a file. Whenever this compressed image is displayed the compression process is reversed, and the image is restored in full.
The Compression Paradox. The two types of compression are: (1) Lossless compression which saves the image quality but unfortunately the level of compression isn't anything to write home about and (2) Lossfull compression which decreases quality, but it can substantially reduce the size of an image.
Lossless compression Lossless compression uncompresses an image so its quality matches the original image. This would be ideal except for the fact that it doesn't provide much compression. A leading lossless compression technique is the LZW (Lempel-Ziv-Welch). This is used in GIF and TIFF files and achieves compression of 50 to 90%. This looks pretty good but when compared with lossfull compression its, simply put, nothing.
Lossfull compression Although lossless compression is possible, it is usually impractical. Therefore, almost all digital cameras use a lossfull compression that degrades images to a certain extent. The more the images are compressed, the more quality they lose. Usually, image degradation isn't visible however, enlarged prints reveal it quite clearly as the pixels become visible and the image gets a blurred look. The trick is to remove data that isn't vital or data that isn't obvious to the viewer. For example, if there is a plain (same shade of color) wall in the background only the value for one pixel needs to be saved along with the locations of all other identical pixels in the image. This reduces duplication of data. The leading lossfull compression scheme is JPEG (Joint Photographic Experts Group) commonly used in JFIF files (JPEG File Interchange Format). The biggest advantage of this scheme is that it allows you to select the degree of compression. Compression ratios for JPEG format range between 10:1 and 40:1.
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