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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} .
In the table below, the column "ISO 8859-1" shows how the file signature appears when interpreted as text in the common ISO 8859-1 encoding, with unprintable characters represented as the control code abbreviation or symbol, or codepage 1252 character where available, or a box otherwise. In some cases the space character is shown as ␠.
Codestream packing: All entropy-coded data are packed into a linear stream of bits (grouped in byte multiples) along with all of the required image metadata. This sequence of bytes is called the codestream and its high-level syntax is based on the typical JPEG markers and marker segments syntax. [29]
Character-based (text) files usually have character-based headers, whereas binary formats usually have binary headers, although this is not a rule. Text-based file headers usually take up more space, but being human-readable, they can easily be examined by using simple software such as a text editor or a hexadecimal editor.
A JPEG image consists of a sequence of segments, each beginning with a marker, each of which begins with a 0xFF byte, followed by a byte indicating what kind of marker it is. Some markers consist of just those two bytes; others are followed by two bytes (high then low), indicating the length of marker-specific payload data that follows.
Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) [5] is a standard that specifies formats for images, sound, and ancillary tags used by digital cameras (including smartphones), scanners and other systems handling image and sound files recorded by digital cameras.
Image ID length (field 1) 0–255 The number of bytes that the image ID field consists of. The image ID field can contain any information, but it is common for it to contain the date and time the image was created or a serial number. As of version 2.0 of the TGA spec, the date and time the image was created is catered for in the extension area.
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: