Re: PngSuite icon with eXIf chunk

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oops :) some version control apparently missing

the old January version of exif2c08.png got included

attached the correct one

thanks Phil !!

Willem



$ hexdump -C exif2c08.png

00  89 50 4e 47 0d 0a 1a 0a  00 00 00 0d 49 48 44 52  |.PNG........IHDR|
10  00 00 00 20 00 00 00 20  08 02 00 00 00 fc 18 ed  |... ... ........|
20  a3 00 00 03 d2 65 58 49  66 4d 4d 00 2a 00 00 00  |.....eXIfMM.*...|
30  08 00 07 01 12 00 03 00  00 00 01 00 01 00 00 01  |................|
40  1a 00 05 00 00 00 01 00  00 00 62 01 1b 00 05 00  |..........b.....|




On 2017-07-17 14:43, Willem van Schaik wrote:
>
> last January I posted a recipe to create a PNG with an exIf chunk
>
> here is the updated version for eXIf and some other changes in the final
> spec
>
[...]

-- 

Willem van Schaik
<[email protected]>
http://www.schaik.com/


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- create in GIMP a simple JPEG image exif-org.jpg

- shrink the image into a tiny thumbnail

  $ jpegtopnm exif-org.jpg | pnmscale -xysize 8 8 | pnmtojpeg -q 90 >
  exif-thp.jpg

- use exiftool to add an APP1 block with EXIF data

  $ exiftool -exif:exifversion=0220 -exif:copyright="2017 Willem
  van Schaik" -exif:usercomment=PngSuite -exif:orientation=horizontal
  -exif:xresolution=72 -exif:yresolution=72 -exif:resolutionunit=inches
  "-thumbnailimage<=exif-thp.jpg" -o exif2c08.jpg exif-org.jpg

- check the EXIF data with both 'exiftool exif2c08.jpg' and the exif tab in eog

- $ hexdump -C exif2c08.jpg | more

  00000000  ff d8 ff e0 00 10 4a 46  49 46 00 01 01 00 00 01  |......JFIF......|
  00000010  00 01 00 00 ff e1 03 da  45 78 69 66 00 00 4d 4d  |........Exif..MM|
  00000020  00 2a 00 00 00 08 00 07  01 12 00 03 00 00 00 01  |.*..............|

  in this 0xffe1 is the APP1 marker, the length is 0x3da or 986, and Exif.. is
  the code, null and padding byte; the data starts with "MM" (or "II")

- snip out the EXIF data (length is 986 - 8 = 978)

  $ dd skip=30 count=978 bs=1 if=exif2c08.jpg of=exif-app.dat

- use dd to cut the PNG file into pieces

  $ dd skip=0 count=33 if=exif-org.png of=exif-one.png
  $ dd skip=33 count=765 if=exif-org.png of=exif-two.png

- create some binary bits and pieces (chunkname eXIf)

  $ echo -n -e "\x00\x00\x03\xd2\x65\x58\x49\x66" > exif-chk.dat
  $ echo -n -e "\x00\x00\x00\x00" > exif-crc.dat

- use cat to glue the whole thing together (with CRC zero)

  $ cat exif-one.png exif-chk.dat exif-app.dat exif-crc.dat
  exif-two.png > exif2c08.png

- finally pngcsum (http://schaik.com/png/pngcsum.html) to fix the CRC

- view with "eog exif2c08.png" and "hexdump -C exif2c08.png"


Willem van Schaik
Calgary, July 2017



On 2017-01-03 19:31, John Bowler wrote:
> ================================================================
> PNG CHUNK PROPOSAL: eXIf
>
> SPECIFICATION
> =============
>
> The four-byte chunk type field contains the decimal values
>
> 101 88 73 102
>
> The eXIf chunk contains EXIF metadata with a length given by the chunk
> length.  Such data shall be compatible with specifications issued by
> CIPA, "Exchangeable image file format for digital still cameras" [CIPA
> DC-008-2016] or its successors.
>
> At most one eXIf chunk shall occur in a PNG stream.  The chunk has no
> chunk-specific positioning requirements; it may appear before or after
> the IDAT chunks.
> ================================================================



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