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

It's not a good idea to use "registered" chunknames for experimental
chunks.

I patched your image to make the test chunk "uxIf" instead of "eXIf",
and added a compressed one called "zxIf" which has a zero compression
method byte followed by zlib-compressed data.

Here are pngcheck -vf results for the three png files (your original and
the two new ones):

glenn.rp> pngcheck -vf *.png
File: exif2c08.png (1794 bytes)
  chunk IHDR at offset 0x0000c, length 13
    32 x 32 image, 24-bit RGB, non-interlaced
  chunk eXIf at offset 0x00025, length 984:  illegal (unless recently
approved) unknown, public chunk
  chunk IDAT at offset 0x00409, length 741
    zlib: deflated, 4K window, default compression
  chunk IEND at offset 0x006fa, length 0
ERRORS DETECTED in exif2c08.png

File: uxif2c08.png (1794 bytes)
  chunk IHDR at offset 0x0000c, length 13
    32 x 32 image, 24-bit RGB, non-interlaced
  chunk uxIf at offset 0x00025, length 984
    unknown private, ancillary, safe-to-copy chunk
  chunk IDAT at offset 0x00409, length 741
    zlib: deflated, 4K window, default compression
  chunk IEND at offset 0x006fa, length 0
No errors detected in uxif2c08.png (4 chunks, 41.6% compression).

File: zxif2c08.png (1438 bytes)
  chunk IHDR at offset 0x0000c, length 13
    32 x 32 image, 24-bit RGB, non-interlaced
  chunk zxIf at offset 0x00025, length 628
    unknown private, ancillary, safe-to-copy chunk
  chunk IDAT at offset 0x002a5, length 741
    zlib: deflated, 4K window, default compression
  chunk IEND at offset 0x00596, length 0
No errors detected in zxif2c08.png (4 chunks, 53.2% compression).

Errors were detected in 1 of the 3 files tested.
No errors were detected in 2 of the 3 files tested.


On Sat, Jan 7, 2017 at 5:08 PM, Willem van Schaik <[email protected]> wrote:

>
> 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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