Re: EXIF support in PNG
"Soni L." <[email protected]>
| Newsgroups | gmane.comp.graphics.png.general |
|---|---|
| Message-ID | <[email protected]> |
On 02/01/17 02:06 AM, Willem van Schaik wrote: > but how can we have a PNG image with an EXIF chunk that says that the > format of the image is JPEG ?? > > again, not talking about the thumbnail > > yep, coordination of this will be very complicated, but it needs to be > resolved > > Willem > Image metadata format that includes metadata about the image format itself instead of just the image? ... How did this get widespread adoption in the first place?! > > > > On 2017-01-01 17:17, John Bowler wrote: >> On Sun, Jan 1, 2017 at 1:18 PM, Willem van Schaik <[email protected] >> <mailto:[email protected]>> wrote: >> >> >> #1 - we have to solve this!! >> looking at the EXIF metadata in eog, I noticed that one of the markers >> is "Compression" so maybe is a need for a change in the EXIF standard, >> namely to add "PNG Compression" (I'm talking here about the main >> picture, not the thumbnail) >> >> >> PNG is not an EXIF supported format, so all that is happening is that a >> PNG file is being used as a carrier for a blob of data from, probably, a >> digital camera so that it can be restored at the end of the day. >> >> Now, if PNG was an EXIF supported format then it would be necessary for >> something that wrote such an EXIF to transcode the field; from >> http://www.exiv2.org/tags.html (non-HTML readers can look the following >> up under tag number 259): >> >> 0x0103 259 Image Exif.Image.Compression Short The compression scheme >> used for the image data. When a primary image is JPEG compressed, this >> designation is not necessary and is omitted. When thumbnails use JPEG >> compression, this tag value is set to 6. >> >> So 'Compression' is the compression of the last EXIF supported file >> format or, maybe, depending on what PhotoShop actually does, of the >> original camera data. (I guess if I owned PhotoShop I'd put a JPEG >> camera file into it and see what came out if I saved it as TIFF...) >> >> If I were writing software to do this I would actually drop IFD[1], the >> thumbnail, from the EXIF data and just store IFD[0] verbatim. I would >> probably come up with a tag exIF and use that, exactly as in JPEG APP1. >> >> >> it is probably tag #103 on page 28 of the JEITA/CIPA spec - or is that >> only for the thumbnail, anyway when the mail image is stored as PNG >> instead of JPEG, that must be reflected in the EXIF data >> >> >> If it's in IFD[0] it refers to the EXIF image and *absent* means JPEG. >> If it is IFD[1] it refers to the thumbnail and *6* means JPEG. At least >> I think that is what the intention is. >> >> >> #2 - of lesser importance >> we could always request the CIPA folks to add in the EXIF standard PNG >> as a fourth compression method for thumbnails; which wouldn't require >> any change to the PNG standard, because from a PNG perspective we >> consider the EXIF chunk a "black box" >> >> >> Yes, true, but personally I would rather let them sort it out. I see >> the HDR applications of 16-bit per channel PNG as something that happens >> as an alternative to TIFF with floating point data or the well-known but >> not widely used exponent+RGB format. I can't imagine that camera >> manufacturers would ever output it, particularly given things like >> SLog3, so I don't imagine that the EXIF guys have any motivation >> whatsoever to support PNG. >> >> -- >> John Bowler <[email protected] >> <mailto:[email protected]>> >> +1 (541) 450-9885 >> PO BOX 3151 >> KERBY OR 97531-3151 >> USA >> >> >> ------------------------------------------------------------------------------ >> Check out the vibrant tech community on one of the world's most >> engaging tech sites, SlashDot.org! http://sdm.link/slashdot >> >> >> >> _______________________________________________ >> png-mng-misc mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/png-mng-misc >> > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot