Commons talk:File types

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Split advice in 'Images' section into new sections 'Photographs' and 'Scans and non-photographic images'[edit]

The section headed 'Images' tries to do too much. It would be better if the section was split into two new sections 'Photographs' for still photographs and 'Scans and non-photographic images' for diagrams, screenshots, and scans of prints and slides. That would make it much easier for users to find the information they need and would allow the advice to be better resolved and tailored. Any comments? Best wishes. RobbieIanMorrison (talk) 11:00, 6 February 2017 (UTC)

Archival format for digital photographs[edit]

The page currently states: PNG is good for ... print-quality photographs. But this advice is questionable and TIFF might offer a better option. TIFF has the advantage of retaining the Exif and (if I am not mistaken) IPTC metadata, including, if the camera supports it, GPS location and timestamp information. It would be really helpful if this recommendation could be resolved and added to this help page. (Note also the discussion above on thumbnail sharpening.) Best wishes. RobbieIanMorrison (talk) 11:09, 6 February 2017 (UTC)

TIFF has a number of its own problems, such as that it's not actually a single image file format, but rather a loose file container for an indefinite number of image subformats, so that it's almost impossible to write a software program that will correctly understand or process all theoretically valid TIFF files. Any kind of metadata can be stored in a PNG file; the real question is having a standard way of doing so, so that different programs can access it. Various people have been working on this, but not sure that anything is widely accepted yet... AnonMoos (talk) 08:15, 7 February 2017 (UTC)
Hello AnonMoos (also Julian Herzog). Thanks for your thoughts. This question certainly needs resolution. I did some trials based on my own workflow using GIMP 2.8.18 on Ubuntu 16.10 (while noting that 2.8.20 is now current). I also searched the web for advice and read the archives for this page. The GIMP development branch (from version 2.9.4.1) now has support for viewing and editing Exif, Adobe XMP, and IPTC metadata and this support will be included in the next production version 2.10.[1][2] This post covers digital photographs and not scanned prints and slides. Some points to take into consideration follow:
TIFF
GIMP 2.8 will not transfer metadata from the RAW file to the exported TIFF file.[3] It makes no difference which GIMP preferences have been set or which TIFF export options (including type of compression or not) have been selected.
GIMP 2.10 will fix this problem. From the draft change log on the GIMP developer wiki:[4]
  • the Image → Image Metadata dialog will show Exif, XMP, and IPTC information
  • PNG, JPEG, and TIFF exporters will now have Save Exif, Save IPTC, and Save XMP options within the Advanced group of settings
In the interim, the metadata can be easily transferred using ExifTool (tested with version 10.23):
$ exiftool -verbose -tagsFromFile image.raw image.tif
PNG
PNG does not officially support Exif. However ImageMagick, ExifTool, and Exiv2 all support a work-around. Phil Harvey (author of ExifTool) posted the following to stackoverflow in 2014:[5]
ImageMagick stores EXIF information in a PNG "Raw profile type APP1" zTXt chunk when converting from JPEG images. This method of storing EXIF in PNG images is also supported by ExifTool (and I believe Exiv2 too), but it is not part of the PNG or EXIF specification.
ExifTool can read, write, or create Exif, XMP, IPTC and ICC (color management) data using a non-standard but somewhat common format.[6] ImageMagick convert will also copy this information across when undertaking a conversion. My trials with Exiv2 version 0.25 001900 (64 bit build) confirm that the utility will also read this metadata (I did not try to create or modify metadata though, but this functionality should also work).
The metadata can be transferred using ExifTool, although this form of metadata storage is not standardized:
$ exiftool -verbose -tagsFromFile image.raw image.png
XCF
XCF (the native GIMP format) is supported by Wikimedia Commons and does contain the Exif metadata embedded in the original RAW file. It is unlikely that Wikimedia Commons will generate a thumbnail from an XCF file, but that is okay because this is an archive format and there will be an associated lower quality JPEG image for general usage.
It did cross my mind to use XCF as an archive format until GIMP 2.10 is released (that could be many months). But I can see some downsides for this as well, including the requirement to have GIMP or GIMP-supporting software to view and manipulate the image file. In addition, (as I understand it) there are no guarantees on the stability of the XCF format. I am also rather tempted to use the development version 2.9.4 of GIMP and the concurrent risks of unresolved software, but there are a ton of dependencies to confront.
After further experimentation, ExifTool provides an ideal solution. The metadata can be shifted from the RAW source programmatically. See the two command lines above. The only outstanding question is whether to choose TIFF or PNG as the archive format. On balance I think TIFF wins out. PNG has the advantage of being almost universally readable on the internet, whereas TIFF has a long history as a raster file format and is widely supported by image viewing and image manipulation applications. Moreover the TIFF standard explicitly supports metadata, while the storage of Exif metadata and such in PNG files is customary at best. The fact that TIFF can be used in diverse ways is not relevant here as we know we are simply repackaging a RAW digital photograph using GIMP or Adobe Photoshop (or some other photographic processing application). Any comments? Best wishes. RobbieIanMorrison (talk) 01:20, 10 February 2017 (UTC)
RobbieIanMorrison -- unfortunately, your procedure reminds me of something I saw in the early 1980s, where the basics of the MS-DOS, Apple II DOS, and TRS-80 TRSDOS operating system file listing, file copying, and file deletion commands were listed, and you were supposed to choose between them on that basis... AnonMoos (talk) 13:54, 10 February 2017 (UTC)

References

  1. GIMP gets advanced Exif, XMP, IPTC metadata support. Libre Graphics World (29 October 2013).
  2. (19 October 2013). "Gimp 2.10 bekommt Metadateneditor für Exif und Co". LinuxMagazin.
  3. GIMP doesn't save EXIF on TIFF files. GIMPUSERS.com.
  4. Release:2.10 changelog : Metadata. GIMP developer wiki.
  5. Does PNG contain EXIF data like JPG?. stackoverflow (23 July 2014).
  6. Harvey, Phil. ExifTool by Phil Harvey. See table displaying supported file types.