DIGITAL CAMERAS-Image Compression & File Formats - Page: 2

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.

DIGITAL CAMERA FILE FORMATS Over the years, a large number of various formats have been developed to store photographs and other bit-mapped images. Every format has its own unique characteristics, which make them more desirable in particular situations. No matter which format is used, it can be altered at will. There are programs available that will convert any image to any of the other commonly used formats. These programs allow you to control compression ratios and therefore image quality.

Raw image file formats Since compression degrades images to some degree, some cameras are able to use an uncompressed format to preserve as much of the captured image quality as possible, this severely reduces the storage capacity of the cameras. In some cases, these raw formats are unique to cameras and are not supported by many other programs, use them only when image quality is indispensable.

JPEG (.JPG) The JPEG (Joint Photographic Experts Group) format, pronounced "jay-peg," is by far the most popular format used for the storage of photographic images. The JPEG format is in widespread use and is compatible with nearly all applications currently available. The JPEG format is optimized for the display of images and doesn't work well for text or lines. As JPEG compression affects the quality of the image, most cameras allow you to control the compression by choosing between different ratios of compression. Cameras allow choices between lower compression and higher image quality or greater compression and poorer quality. Higher compression is used only when more and more images are to be stored in the limited amount of memory available. Higher compression also makes further use of images, such as posting them on the web, easier.

TIFF (.TIF) TIFF (Tag Image File Format) was developed by Aldus Corporation for saving images created by scanners, photo editing programs, frame grabbers etc. This format is mostly used for transferring images and has gained wide acceptance in this regard. TIFF format is widely used in desktop publishing applications. Several variations have been developed for different uses and occasionally there are problems of compatibility, but over all this is a good format to use.

MPEG MPEG (Motion Pictures Expert Group) is a compressed audio/video format. It comes in two formats MPEG-1 and MPEG-2. MPEG-1 has been developed for systems, such as computers/monitors, that use non-interlaced displays. Some digital cameras use this format to capture short audio/video. The problem is that MPEG-1's image quality is not as good as that of VHS tape. Here the dilemma is between quality and ease of use. A newer variation, MPEG-2 has been developed for interlaced displays. MPEG-2 is an exceptionally high quality format, with quality superior to that of the laser disks and DVDs. MPEG does take more space than other compression formats but the quality makes up for this deficiency.