Learning level: - Basic
Learning time: - 25 minutes
Today, the most used and popular image file format is JPEG format. All digital camera and any other image capture devices use JPEG file format to create an actual image. JPEG file is also the easiest way to display the photographs with smooth variations of color tone. It has 24 Bit color depth which includes 16 million color values. JPEG stands for Joint Photographic Experts Group. 'JPEG' is pronounced correctly as ‘Je-peg’ (जेपेग).
JPEG also known as ‘Lossy File format’ because some data information lost in every time edit and saving process with image editing software. Losing an information tends to degrade the picture quality. Minimal information will be lost even if copy and paste a file at another location. Everyone knows that JPEG is an image file format but actually it was not standard file format before transmission and compression standardization integrated in 1992.
In1982, the International Organization for Standardization (ISO) formed the Photographic Expert Group (PEG) to research methods of transmitting video, still images and text over ISDN (Integrated Services Digital Network) lines. PEG’s goal was to produce a set of industry standards for transmission of graphics and image data over digital communications networks.
In 1986, a subgroup of the International Telephone and Telegraph Consultative Committee (CCITT) began to research methods of compressing color and gray-scale data for facsimile transmission. The compression methods needed for color facsimile systems were very similar to those being researched by PEG. It was therefore agreed that the two groups should combine their resources and work together towards a single standard.
In 1987, the IOS and CCITT combined their two groups into a joint committee that would research and produce a single standard of image data compression for both organizations to use. This new committee was Joint Photographic Experts Group (JPEG). In 1987, ISO TC 97 became ISO/IEC JTC1 and in 1992, CCITT became ITU-T (ITU Telecommunication Standardization Sector)
- ITU = International Telecommunication Union (Formerly – International Telegraph Union)
- ITU-T = ITU Telecommunication Standardization Sector
- Facsimile transmission = An international system of transmitting a written, printed or pictorial document over the telephone system by scanning in photoelectrically and reproducing the image after transmission, often shortened to fax.
Several additional standards were evolved to address these issues, among them, two major standards became very effective and popular.
1) Exchangeable image file format (Exif) Image files that employ JPEG compression are commonly called ‘JPEG files’ and are stored in variants of the JPEG Interchange Format (JIF) standard. Most image capture devices (such as digital cameras) create JPEG files which are actually in the Exif format. Exif format is standardized format for metadata interchange in camera industries. On the other hand, since the Exif standard does not allow color profiles. Most image editing software stores JPEG in JFIF format and also include the Exif file to include the metadata. The JFIF standard is interpreted somewhat flexibly. Exif is sometimes referred to as JPEG/Exif.
2) JPEG File Interchange Format (JFIF) This is a minimal file format which enables JPEG bit streams (ITU-T recommendation T.81|ISO/IEC 10918-1) to be exchanged between a wide variety of platforms and applications. Only purpose of this simplified format is to allow the exchange of JPEG compressed images. This format does not include any of the advanced features found in the TIFF specification or any application-specific file format.
JFIF format for exchange JPEG encode files compliant with the JPEG interchange Format (JIF) standard. It solves some of JIF’s limitations in regard to simple JPEG encoded file interchange. As with all JIF compliant files, image data in JFIF files is compressed using the techniques in the JPEG standard. Hence, JFIF is also sometimes referred to as JPEG/JFIF.
The first JPEG standard issued in 1992 and updated version issued in 1994. Exif and JFIF both of these formats use the actual JPEG Interchange Format (JIF) standard. The Exif and JFIF define commonly used file formats for interchange of JPEG-compression images. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices. JPEG/JFIF is the most common format for storing and transmitting photographic images on the World Wide Web.
After the transmission and compression standardization JPEG/Exif and JPEG/JFIF commonly used as JPEG image format and known as compressed or lossy image file format. JPEG compression can be applied 2:1 to 100:1 or more ratios. JPEG compression is necessary process to minimize the file size of images.
In Adobe Photoshop, JPEG files can be saved in the specific compression level with selectable range. There is multiple compression level option in Photoshop as Quality range from (0) to (12).
- Selecting Quality 0, 1, 2, 3, 4 (output Low Quality image with Maximum compression)
- Selecting Quality 5, 6, 7 (output Medium Quality image with Higher compression)
- Selecting Quality 8, 9 (output High Quality image with Lower compression)
- Selecting Quality 10, 11, 12 (output Maximum Quality image with Lowest compression)
Users can choose compression level as per they need. Choosing a lower number results in higher compression and output smaller file size and generates ‘artifacts’ in image. Higher compression also lost color tone and details so that degrade picture quality.
JPEG filename extensions
JPEG files usually have a filename extension of .jpg or .jpeg but .jpe .jfif and .jif are also used.
Wikipedia, JPEG, https://en.wikipedia.org/
File Format Info, JPEG Compression, http://www.fileformat.info/
ECMA International, JPEG File Interchange Format (JFIF), 1st edition/ June 2009 (PDF)
The Sheridan Group, JPEG Compression, (PDF)