README.ijg: Wordsmith per ISO/ITU-T suggestions
This commit merges the following paragraph from the latest libjpeg
release:
https://github.com/libjpeg-turbo/ijg/blob/jpeg-9c/README#L222-L229
which takes into account the fact that JFIF is now an official ISO/ITU-T
standard. I also included the ISO/IEC document number for the JFIF spec
(jpeg-9c included only the ITU-T rec number.)
This commit also heavily wordsmiths the "FILE FORMAT WARS" section.
In jpeg-7 and later, this section has become somewhat impolitic,
referring to JPEG 2000 and JPEG XR as "faulty technologies" and
"momentary mistakes." The original intent of this section, which was
introduced in jpeg-5 and refined in jpeg-6
(https://github.com/libjpeg-turbo/ijg/blob/jpeg-5/README#L317-L338,
https://github.com/libjpeg-turbo/ijg/blob/jpeg-6b/README#L335-L367)
was to highlight the problem of JPEG file format divergence that existed
in the 1990s prior to the adoption of JFIF as an official ISO/ITU-T
standard. That problem is fortunately no longer a problem, thanks in
part to the existence of libjpeg. I have attempted to preserve Tom's
intent of using this section to describe which file formats the code is
compatible with and why it isn't compatible with some file formats
bearing the name "JPEG." Such modifications always put our project in a
very awkward position, because we are not the IJG and do not claim to
be, but it is still necessary for us to modify the IJG README file from
time to time to eliminate obsolete information while attempting to
remain as neutral as possible.
diff --git a/README.ijg b/README.ijg
index ee9fb67..c4eb7db 100644
--- a/README.ijg
+++ b/README.ijg
@@ -214,14 +214,14 @@
numbers ISO/IEC IS 10918-2, ITU-T T.83.
The JPEG standard does not specify all details of an interchangeable file
-format. For the omitted details we follow the "JFIF" conventions, revision
-1.02. JFIF 1.02 has been adopted as an Ecma International Technical Report
-and thus received a formal publication status. It is available as a free
-download in PDF format from
-http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
-A PostScript version of the JFIF document is available at
-http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at
-http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
+format. For the omitted details, we follow the "JFIF" conventions, revision
+1.02. JFIF version 1 has been adopted as ISO/IEC 10918-5 (05/2013) and
+Recommendation ITU-T T.871 (05/2011): Information technology - Digital
+compression and coding of continuous-tone still images: JPEG File Interchange
+Format (JFIF). It is available as a free download in PDF file format from
+https://www.iso.org/standard/54989.html and http://www.itu.int/rec/T-REC-T.871.
+A PDF file of the older JFIF 1.02 specification is available at
+http://www.w3.org/Graphics/JPEG/jfif3.pdf.
The TIFF 6.0 file format specification can be obtained by FTP from
ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme
@@ -253,18 +253,22 @@
send usenet/news.answers/jpeg-faq/part2
-FILE FORMAT WARS
-================
+FILE FORMAT COMPATIBILITY
+=========================
-The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together
-with ITU-T SG16) currently promotes different formats containing the name
-"JPEG" which are incompatible with original DCT-based JPEG. IJG therefore does
-not support these formats (see REFERENCES). Indeed, one of the original
-reasons for developing this free software was to help force convergence on
-common, interoperable format standards for JPEG files.
-Don't use an incompatible file format!
-(In any case, our decoder will remain capable of reading existing JPEG
-image files indefinitely.)
+This software implements ITU T.81 | ISO/IEC 10918 with some extensions from
+ITU T.871 | ISO/IEC 10918-5 (JPEG File Interchange Format-- see REFERENCES).
+Informally, the term "JPEG image" or "JPEG file" most often refers to JFIF or
+a subset thereof, but there are other formats containing the name "JPEG" that
+are incompatible with the DCT-based JPEG standard or with JFIF (for instance,
+JPEG 2000 and JPEG XR). This software therefore does not support these
+formats. Indeed, one of the original reasons for developing this free software
+was to help force convergence on common, interoperable format standards for
+JPEG files.
+
+JFIF is a minimal or "low end" representation. TIFF/JPEG (TIFF revision 6.0 as
+modified by TIFF Technical Note #2) can be used for "high end" applications
+that need to record a lot of additional data about an image.
TO DO
