Re: EXIF support in PNG - PngSuite image with EXIF chunk

I created a PNG with EXIF chunk for PngSuite

how I did it:

- created 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

- used 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 'eog exif2c08.jpg' and 'exiftool'

- snipped out the EXIF data

   $ dd skip=24 count=984 bs=1 if=exif2c08.jpg of=exif-app.dat

- using dd to cut a PNG file into pieces

- create some binary bits and pieces

   $ echo -n -e "\x00\x00\x03\xd8\x65\x58\x49\x66" > exif-chk.dat
   $ echo -n -e "\x00\x00\x00\x00" > exif-crc.dat

- used 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

attached the results

view it with "hexdump -C exif2c08.png"

Willem



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.
> ================================================================


-- 

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

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