Re: EXIF support in PNG

On Thu, Jan 5, 2017 at 10:06 AM, Glenn Randers-Pehrson <[email protected]>
wrote:

>
>
> On Wed, Jan 4, 2017 at 11:10 PM, John Bowler <
> [email protected]> wrote:
>
>> On Wed, Jan 4, 2017 at 8:02 PM, Glenn Randers-Pehrson <[email protected]>
>> wrote:
>> > It's more like about 25 lines of Fortran in my case,
>> > assuming adler32 and crc32 functions are available, compared
>> > to around 10 lines to write a raw EXIF profile wrapped in
>> > an EXIF chunk length, "eXIf", data, and crc.
>>
>> Ok, please post those 25 lines.
>>
>

glenn.rp> cat dunflate.f
      program dunflate

c     Written in 2017 by Glenn Randers-Pehrson <[email protected]>
c
c     To the extent possible under law, the author has dedicated all
copyright
c     and related and neighboring rights to this software to the public
domain
c     worldwide. This software is distributed without any warranty.
c     See <http://creativecommons.org/publicdomain/zero/1.0/>.
c
c     FIRST DRAFT 5 January 2017
c
c
c     Demonstrates writing a PNG chunk with zlib-encoded but
c     uncompressed data, in a form that any compliant zlib reader
c     can decode.  This demonstration uses the iCCP chunk
c     but could also be used with zTXt or a proposed eXIf chunk.

c     input (on stdin): a raw ICC profile
c     output( on stdout): an iCCP chunk containing the profile in a
c        zlib-encoded but uncompressed format.

c     calculate ADLER32 over uncompressed
c       data, get uncompressed data length
c       (implementation detail: do this on
c       a separate pre-pass or do it all in
c       one pass.

c     number_of_blocks =
c       uncompressed_data_length / (64k-1)

c     deflated_bytes = uncompressed_data_length
c        + 5 * number_of_blocks

c     zlib header:
c       cmf = 8,30 (32k+30)

      remaining_length = deflated_bytes

c     if (not last block i.e., remaining_length > 64k-1)
c         block header:
c           128 (1, 00, xxxxx) [check on position of the "1"]
c           64k-1 (2 bytes block_len)
c           0     (2 bytes block_nlen)
c         some data
c         note: these blocks are 64k+4 bytes in length
          remaining_data -= 64k-1
c     else
c         block header:
c           0 (0, 00, xxxxx)
c           block_len = 2 bytes, lsb first)
c           block_nlen = ~len (2 bytes, lsb first)
c         remaining data
c         note: this block is 5 to 64k+4 bytes in length

c     calculate length and crc32 over
c         "iCCP", zero, cmf, blocks, and adler32

c     write length
c     write "iCCP"
c     write "0" (1 byte, "compression method")
c     write zlib header
c     write blocks
c     write ADLER32

      end

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