PNG eXIf chunk proposals January 2017

This directory contains test files with various
proposed PNG chunks to hold an Exif profile.
These chunks use the unregistered chunk name
"exIf".  Eventually, if approved by the PNG
Development Group, a registered name (probably
"eXIf") will be specified.

The canon_e135 directory contains a photo by
Nancy Randers-Pehrson from a 2013 Canon Powershot
Elph 135 camera.  The Exif profile represents the
photograph before it was edited to reduce the main
image to 25% of the original size.

The nikon_b700 directory contains a photo by
Nancy Randers-Pehrson from a 2016 Nikon 700B camera.
The Exif profile represents the photograph before
it was edited to reduce the main image dimensions
and to apply a transform to straighten up the
perspective.

The sony_a300 directory contains a photo by
Glenn Randers-Pehrson from a 2009 Sony Alpha 300
camera, containing a preview representing the
photograph before it was cropped and rescaled to
reduce the main image dimensions.

The willem directory contains a hand-build artificial
32x32 image with a small Exif profile made with GIMP.
It is an "MM"-style (big-endian) profile.

The magick directory will contain the user_chunk_fn()
used in ImageMagick and GraphicsMagick to read and write
HEX-encoded Exif profiles.

Each image directory contains
   o file.jpg: the original JPEG

   o file.exif: the Exif profile extracted from
     the JPEG by the ImageMagick command
     magick file.jpg file.exif (it begins with
     the JFIF ExifIF "Exif\0\0")

   o file_exIf.chunk: an exIf chunk containing
     <length><exIf><raw profile data without ExifID><crc32>

   o file_exIf.png: a PNG file containing the exIf chunk
     according to the latest proposal.

   o file_imhex.png: PNG image with the Exif profile, with ExifID,
     hex-encoded and conveyed in a zTXt chunk by ImageMagick

   o file_gmhex.png: PNG image with the Exif profile, with ExifID,
     hex-encoded and conveyed in a zTXt chunk by GraphicsMagick

   o file_exIf.txt: output of "pngcheck -v file_exIf.png"
     and "xxd file_uxIf.png | head -5"

   o file_zxIf.*: a PNG file and chunk data file chunk containing
     <length><zxIf><0><compressed raw profile data without ExifID><crc32>
     according to the latest zxIF proposal (2017-0128).

   o file_uxIf.*: a PNG file and chunk data file chunk containing
     <length><uxIf><raw profile data without ExifID><crc32>
     according to the latest zxIF proposal (this is the same as
     file_exIf.* except for the chunk name).

   o file_exIf_pc.png: result of "pngcrush -ext _pc.png file_exIf.png"

   o file_zxIf_pc.png: result of "pngcrush -ext _pc.png file_zxIf.png"

Unless otherwise indicated, the files in this directory are copyright
2017 by the respective authors and released under the Creative Commons
Attribution 4.0 International license
(CC-BY-4.0; see https://creativecommons.org/licenses/by/4.0/)