JFIF
From Just Solve the File Format Problem
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The presence of a JFIF segment implies that: | The presence of a JFIF segment implies that: | ||
| − | * If the image has three components, its color format is YCbCr. If it has one component, its color format is grayscale. | + | * If the image has three components, its color format is YCbCr, using a conversion formula given in the specification. If it has one component, its color format is grayscale. |
* The image has a particular orientation. | * The image has a particular orientation. | ||
* If the image is subsampled, it uses a particular subsampling position. | * If the image is subsampled, it uses a particular subsampling position. | ||
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Valid JFIF files begin with <code>FF D8 FF E0 ?? ?? 'J' 'F' 'I' 'F' 00</code>. Some technically-invalid files exist in which the JFIF segment has been relocated, and for them this signature will not match. | Valid JFIF files begin with <code>FF D8 FF E0 ?? ?? 'J' 'F' 'I' 'F' 00</code>. Some technically-invalid files exist in which the JFIF segment has been relocated, and for them this signature will not match. | ||
| − | == | + | == Versions == |
* JFIF 1.00 (PRONOM: {{PRONOM|fmt/42}}) was the original version. | * JFIF 1.00 (PRONOM: {{PRONOM|fmt/42}}) was the original version. | ||
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* JFIF 1.02 (September 1, 1992; PRONOM: {{PRONOM|fmt/44}}) added an optional JFXX segment, capable of storing a compressed thumbnail image. | * JFIF 1.02 (September 1, 1992; PRONOM: {{PRONOM|fmt/44}}) added an optional JFXX segment, capable of storing a compressed thumbnail image. | ||
| − | * JFIF 2.xx (2014 | + | * JFIF 2.xx (~2014): Starting with version 9a, the Independent JPG Group's software supports "JFIF 2.01" (e.g. using <code>cjpeg -bgycc</code>), which apparently implies that that the image uses "big gamut YCC". We have not located any specifications for this JFIF version. |
== Specifications == | == Specifications == | ||
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* [http://www.w3.org/Graphics/JPEG/jfif3.pdf JFIF version 1.02] | * [http://www.w3.org/Graphics/JPEG/jfif3.pdf JFIF version 1.02] | ||
* [http://www.itu.int/rec/T-REC-T.871/en ITU-T Rec. T.871] (not free to download) | * [http://www.itu.int/rec/T-REC-T.871/en ITU-T Rec. T.871] (not free to download) | ||
| − | + | * [http://www.ecma-international.org/publications/files/ECMA-TR/TR-098.pdf ECMA TR/98] (JFIF 1.02) | |
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== Links == | == Links == | ||
Revision as of 21:30, 19 January 2014
JFIF (JPEG File Interchange Format) is a standard that defines a portable subset of the JPEG file format. Most of the JPEG files in existence conform to JFIF.
JFIF defines JPEG application segments which serve to identify JFIF files, and to store a small amount of metadata: the pixel density, and a thumbnail image.
The presence of a JFIF segment implies that:
- If the image has three components, its color format is YCbCr, using a conversion formula given in the specification. If it has one component, its color format is grayscale.
- The image has a particular orientation.
- If the image is subsampled, it uses a particular subsampling position.
JFIF was developed based on a draft version of the JPEG standard, which is how it can predate JPEG's official 1992 publication date.
Contents |
Disambiguation
Don't confuse JPEG File Interchange Format with JPEG Interchange Format. The former is JFIF; the latter means approximately the same thing as JPEG.
Identification
Valid JFIF files begin with FF D8 FF E0 ?? ?? 'J' 'F' 'I' 'F' 00. Some technically-invalid files exist in which the JFIF segment has been relocated, and for them this signature will not match.
Versions
- JFIF 1.00 (PRONOM: fmt/42) was the original version.
- JFIF 1.01 (December 10, 1991; PRONOM: fmt/43) may have changed the subsampling position to centered.
- JFIF 1.02 (September 1, 1992; PRONOM: fmt/44) added an optional JFXX segment, capable of storing a compressed thumbnail image.
- JFIF 2.xx (~2014): Starting with version 9a, the Independent JPG Group's software supports "JFIF 2.01" (e.g. using
cjpeg -bgycc), which apparently implies that that the image uses "big gamut YCC". We have not located any specifications for this JFIF version.
Specifications
- JFIF version 1.01
- JFIF version 1.02
- ITU-T Rec. T.871 (not free to download)
- ECMA TR/98 (JFIF 1.02)
