Re: DRAFT: eXIf 2017-03-02

08.03.2017 8:40, Cosmin Truta пишет:
> The IFD1 preview is not a purpose in itself, but a secondary
> by-product of importing the EXIF design. We adopt it in order to stay
> compliant to the EXIF design. Implementors may or may not find a
> benefit in it. We should not the break the IFD1 apart, regardless.
Note, that without IFD[1] eXIf still will be compliant to EXIF design.
There is no need to specify that IFD[1] is thumbnail or even allow it to 
make eXIf fit CIPA DC-008-2016.
If you think thumbnail is bad idea - lets forbid it. Like extra 
specification of width and height is forbidden for EXIF in JPEG.
> I repeat what I had said before: all of the other non-TIFF image
> formats that are EXIF containers (JPEG/WebP/JPEG-2000/BPG/etc/etc)
> happen to have a tagged structure, just like PNG; and yet, none of
> them break the EXIF apart. Neither should we.
Most of these formats have very limited support for metadata and use 
EXIF from start.
PNG is completely different: there is tEXt chunks (and pHYs and sTER). 
So usage EXIF same way as JPEG will ruin compatibility with existing PNG 
software: EXIF data will be ignored by current software; tEXt and pHYs 
could be ignored if parser read only EXIF(like it's supposed for WebP).

Also: at least BPG have it's own preview structure.
> The EXIF structure is monolithic. The existing hardware and software
> is not necessarily prepared to handle an EXIF structure broken apart,
> especially because nobody else breaks it.
In fact - no. EXIF specification is not monolithic. It consists of at 
least four parts: TIFF attributes; EXIF sub-IFD; GPS sub-IFD; Thumbnail.
Existing software may handle it as monolithic or may not. Because nobody 
tried to adopt EXIF into format with developed metadata (at least like TGA).
Anyway support for PNG attributes to keep compatibility with existing 
PNG software I treat as much complex redesign than ignore(don't write) 
thumbnail or even handle EXIF IFD separated from TIFF IFD[0].

One day PNG and it's implementations was monolithic. Later JNG was 
designed and use sCAL, tEXt, tIME, iCCP without pCAL, PLTE, IHDR...

May be it's possible to design new image format which use PNG 
compression and EXIF attributes. Like reverse JNG - PNF(PNg+exiF) for 
example.
With forbidding most of PNG metadata chunks and rely only on EXIF it 
will be possible for such format to be easily implemented by existing 
EXIF-capable software.

-- 
Have a nice DOS.

Pavel Zlatovratskii [email protected]; [email protected]


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