Download A Jpeg Image __TOP__
Alexander Rodriguez
tl;dr There is no MIME type image/jpg; there is image/jpeg. However, there is much variation in official documented mappings between files with file name extension .jpg and MIME types. But in practice, nearly all software handles image files named *.jpg in an expected manner
This particular topic is confusing because the varying association of file name extension associated to a MIME type depends which organization created the table of file name extensions to MIME types. In other words, file name extension .jpg could be many different things, "officially" (but in practice is always a JPEG image).
Another confusing thing is RFC 3745 does not appear to match IANA Media Types yet the same RFC is supposed to inform the IANA Media Types document. For example, in RFC 3745 .jpf is preferred file extension for image/jpx but in IANA Media Types the name jpf is not present (and that IANA document references RFC 3745!).
The most official seeming document by IANA is surprisingly inadequate. No MIME type is registered for file extension .jpg yet there exists the odd vnd.sealedmedia.softseal.jpg. File extension.JPEG is only known as a video type while file extension .jpeg is an image type (when did lowercase and uppercase letters start mattering!?). At the same time, jpeg2000 is type video yet RFC 3745 considers JPEG 2000 an image type! The IANA list seems to cater to company-specific jpeg formats (e.g. vnd.sealedmedia.softseal.jpg).
One side effect of this limitation is that some file extensions, such as .gif match their Mime Type, image/gif, while others are compromised. This includes image/jpeg whose extension is shortened to .jpg. Even in modern Windows, where the limitation is lifted, Microsoft never let the past go, and so the file extension is still the shortened version.
Legacy versions of Internet Explorer took the liberty of uploading jpeg files with the Mime Type of image/pjpeg, which, of course, just means more work for everybody else. They also uploaded png files as image/x-png.
JPEG (/ˈdʒeɪpɛɡ/ JAY-peg, short for Joint Photographic Experts Group)[2] is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality.[3] Since its introduction in 1992, JPEG has been the most widely used image compression standard in the world,[4][5] and the most widely used digital image format, with several billion JPEG images produced every day as of 2015.[6]
The Joint Photographic Experts Group created the standard in 1992.[7] JPEG was largely responsible for the proliferation of digital images and digital photos across the Internet and later social media.[8][circular reference] JPEG compression is used in a number of image file formats. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices; along with JPEG/JFIF, it is the most common format for storing and transmitting photographic images on the World Wide Web.[9] These format variations are often not distinguished and are simply called JPEG.
The MIME media type for JPEG is "image/jpeg," except in older Internet Explorer versions, which provide a MIME type of "image/pjpeg" when uploading JPEG images.[10] JPEG files usually have a filename extension of "jpg" or "jpeg". JPEG/JFIF supports a maximum image size of 65,53565,535 pixels,[11] hence up to 4 gigapixels for an aspect ratio of 1:1. In 2000, the JPEG group introduced a format intended to be a successor, JPEG 2000, but it was unable to replace the original JPEG as the dominant image standard.[12]
The JPEG specification also cites three other patents from IBM. Other companies cited as patent holders include AT&T (two patents) and Canon Inc.[1] Absent from the list is U.S. Patent 4,698,672, filed by Compression Labs' Wen-Hsiung Chen and Daniel J. Klenke in October 1986. The patent describes a DCT-based image compression algorithm, and would later be a cause of controversy in 2002 (see Patent controversy below).[13] However, the JPEG specification did cite two earlier research papers by Wen-Hsiung Chen, published in 1977 and 1984.[1]
The JPEG standard specifies the codec, which defines how an image is compressed into a stream of bytes and decompressed back into an image, but not the file format used to contain that stream.[19]The Exif and JFIF standards define the commonly used file formats for interchange of JPEG-compressed images.
In 2002, Forgent Networks asserted that it owned and would enforce patent rights on the JPEG technology, arising from a patent that had been filed on October 27, 1986, and granted on October 6, 1987: U.S. Patent 4,698,672 by Compression Labs' Wen-Hsiung Chen and Daniel J. Klenke.[13][24] While Forgent did not own Compression Labs at the time, Chen later sold Compression Labs to Forgent, before Chen went on to work for Cisco. This led to Forgent acquiring ownership over the patent.[13] Forgent's 2002 announcement created a furor reminiscent of Unisys' attempts to assert its rights over the GIF image compression standard.
Beginning in August 2007, another company, Global Patent Holdings, LLC claimed that its patent (U.S. Patent 5,253,341) issued in 1993, is infringed by the downloading of JPEG images on either a website or through e-mail. If not invalidated, this patent could apply to any website that displays JPEG images. The patent was under reexamination by the U.S. Patent and Trademark Office from 2000 to 2007; in July 2007, the Patent Office revoked all of the original claims of the patent but found that an additional claim proposed by Global Patent Holdings (claim 17) was valid.[32] Global Patent Holdings then filed a number of lawsuits based on claim 17 of its patent.
Beginning in 2011 and continuing as of early 2013, an entity known as Princeton Digital Image Corporation,[39] based in Eastern Texas, began suing large numbers of companies for alleged infringement of U.S. Patent 4,813,056. Princeton claims that the JPEG image compression standard infringes the '056 patent and has sued large numbers of websites, retailers, camera and device manufacturers and resellers. The patent was originally owned and assigned to General Electric. The patent expired in December 2007, but Princeton has sued large numbers of companies for "past infringement" of this patent. (Under U.S. patent laws, a patent owner can sue for "past infringement" up to six years before the filing of a lawsuit, so Princeton could theoretically have continued suing companies until December 2013.) As of March 2013, Princeton had suits pending in New York and Delaware against more than 55 companies. General Electric's involvement in the suit is unknown, although court records indicate that it assigned the patent to Princeton in 2009 and retains certain rights in the patent.[40]
The JPEG compression algorithm operates at its best on photographs and paintings of realistic scenes with smooth variations of tone and color. For web usage, where reducing the amount of data used for an image is important for responsive presentation, JPEG's compression benefits make JPEG popular. JPEG/Exif is also the most common format saved by digital cameras.
However, JPEG is not well suited for line drawings and other textual or iconic graphics, where the sharp contrasts between adjacent pixels can cause noticeable artifacts. Such images are better saved in a lossless graphics format such as TIFF, GIF, PNG, or a raw image format. The JPEG standard includes a lossless coding mode, but that mode is not supported in most products.
As the typical use of JPEG is a lossy compression method, which reduces the image fidelity, it is inappropriate for exact reproduction of imaging data (such as some scientific and medical imaging applications and certain technical image processing work).
JPEG uses a lossy form of compression based on the discrete cosine transform (DCT). This mathematical operation converts each frame/field of the video source from the spatial (2D) domain into the frequency domain (a.k.a. transform domain). A perceptual model based loosely on the human psychovisual system discards high-frequency information, i.e. sharp transitions in intensity, and color hue. In the transform domain, the process of reducing information is called quantization. In simpler terms, quantization is a method for optimally reducing a large number scale (with different occurrences of each number) into a smaller one, and the transform-domain is a convenient representation of the image because the high-frequency coefficients, which contribute less to the overall picture than other coefficients, are characteristically small-values with high compressibility. The quantized coefficients are then sequenced and losslessly packed into the output bitstream. Nearly all software implementations of JPEG permit user control over the compression ratio (as well as other optional parameters), allowing the user to trade off picture-quality for smaller file size. In embedded applications (such as miniDV, which uses a similar DCT-compression scheme), the parameters are pre-selected and fixed for the application.
The compression method is usually lossy, meaning that some original image information is lost and cannot be restored, possibly affecting image quality. There is an optional lossless mode defined in the JPEG standard. However, this mode is not widely supported in products.
There is also an interlaced progressive JPEG format, in which data is compressed in multiple passes of progressively higher detail. This is ideal for large images that will be displayed while downloading over a slow connection, allowing a reasonable preview after receiving only a portion of the data. However, support for progressive JPEGs is not universal. When progressive JPEGs are received by programs that do not support them (such as versions of Internet Explorer before Windows 7)[41] the software displays the image only after it has been completely downloaded.
df19127ead