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The bytes s1 and s2 are taken together to represent a big-endian 16-bit integer specifying the length of the following "data bytes" plus the 2 bytes used to represent the length. In other words, s1 and s2 specify the number of the following data bytes as 256 ⋅ s 1 + s 2 − 2 {\displaystyle 256\cdot s1+s2-2} .
Hex signature ISO 8859-1 Offset Extension Description 23 21 #! 0 Script or data to be passed to the program following the shebang (#!) [1]: 02 00 5a 57 52 54 00 00 00 00 00 00 00 00 00 00
For information, the uncompressed 24-bit RGB bitmap image below (73,242 pixels) would require 219,726 bytes (excluding all other information headers). The filesizes indicated below include the internal JPEG information headers and some metadata. For highest quality images (Q=100), about 8.25 bits per color pixel is required.
The JPEG committee was created in 1986 [11] [12] and the Joint (CCITT/ISO) Bi-level Image Group (JBIG) was created in 1988. [11] Former chairs of JPEG include Greg Wallace of Digital Equipment Corporation and Daniel Lee of Yahoo. Fumitaka Ono of Tokyo Polytechnic University was chair of the former JBIG group that has since been merged into JPEG.
The JPEG filename extension is JPG or JPEG. Nearly every digital camera can save images in the JPEG format, which supports eight-bit grayscale images and 24-bit color images (eight bits each for red, green, and blue). JPEG applies lossy compression to images, which can result in a significant reduction of the file size.
(The length unit itself is specified by the tag ResolutionUnit.) By default, these tags in combination are set to 72 pixels per inch (ppi). [19] These tags were inherited from the TIFF 6.0 standard and are required [20] even though for images produced by digital cameras, image resolution values such as ppi are meaningless. [21]
JPEG XL has features aimed at web delivery such as advanced progressive decoding, [40] embedded previews, and minimal header overhead, as well as features aimed at image editing and digital printing, such as support for multiple layers, CMYK, and spot colors. It also supports animated images. The main features are: [41] [42] [43] Compression:
The current standard that defines NITF 2.1 is the Joint BIIF Profile (JBP), version 2024.1 (JBP-2024.1), dated 13 June 2023, which superseded MIL-STD-2500C CN2 in June 2024. The JBP is a profile of ISO/IEC 12087-5, Basic Image Interchange Format, in lieu of the previous military standards.