Does the .png image format have a text metadata field?

In article , Mayayana
wrote:

A TIF is basically a zipped BMP.

false.

tiff is normally uncompressed and has little in common with the bmp
format.

On Thu, 13 Feb 2020 19:05:04 -0500, "Mayayana"
wrote:

"Shadow" wrote

| Since almost all image formats are compressed, do you know a
| tool that can un-compress the data to look for "hidden" text or files?
| There's a lot of apps that do steganography, so there must be
| something to identify the method used (a generic un-packer).
| The NSA would be naked without one. LOL.
|

Mysterious. So it hides extra bytes? Since each format
is different I don't know of any easy way to track it, or
to create the hidden text.

No, it calculates the "empty space" in the image file and uses
that to hide the file/data. To casual user using an image viewer, the
image would appear unaltered. Same size, date and even EXIF data -
only the checksum would differ - but who checks that?
Apart from you, of course.

[]'s

--
Don't be evil - Google 2004
We have a new policy - Google 2012

"Java Jive" wrote

| I only know for sure what I posted earlier, but it may be relevant that
| most of the TIFFs I've encountered have been conversions from the native
| image formats of Canon S40 and Nikon D5600 cameras. The example earlier
| was a TIFF from a CRAW image format of the Canon, converted to TIFF and
| by Canon's own software that came with the camera from an images saved
| by the camera as RAW rather than JPEG, and thence to PNG for use on my
| web site. For a Nikon example: 24.6MB NEF (I *think* their version of
| TIFF, but it could be their version of RAW) comes out as 10.MB PNG.

Yes, I think NEF is RAW. I seem to remember
there can also b special kinds of TIF, but I'm not
really familiar with it. I only know TIFs as the
standard Windows format -- a zipped BMP. So
I typically only use them to store photos saved
from RAW or JPG that I might work on or use
in the future.

John,

Can you explain in baby steps how you get to the "image properties -
summary dialog",

All I have to do, on XP, is to rightclick a file and select "properties"
from the popup menu.

I than get a dialog with two tabs, "General" and "Summary". Clicking the
"Summary" tab gives me a "page" with a button at the bottom showing either
" Simple" or "Advanced ". When it shows "Advanced " the page above
it shows textboxes named, from the top, "Title", "Subject", "Author",
"Category", "Keywords" and "Comments".

But ... As you have W7 what you see might be rather different.

I was looking for an image to show you what I see, but could not find
anything better than the below. Just ignore the "Security" tab:

http://www.cs.mun.ca/jdk1.6/technote.../security2.gif

I'm not disbelieving you, just not sure where you're starting from.

From a different version of Windows than you are looking at. :-)

You might be looking at something like this:

https://www.sevenforums.com/attachme...-details-1.jpg

(notice the "comments" entry directly above the big, red, right-pointing
arrow)

Regards,
Rudy Wieser

Shadow,

Since almost all image formats are compressed, do you know a
tool that can un-compress the data to look for "hidden" text or files?
There's a lot of apps that do steganography,

What makes you think that steganography is limited to the uncompressed data
? :-p

One form of it might make use of a slightly altered compression engine,
which returns the same uncompresed (short) byte sequences for two input
values, and regard those two input sequences as being a Zero and One.

As for your question, a standard Windows installation comes with a few DLLs
(GDI, GDI+) that will uncompress images (into memory) and allow you to
inspect their contents (using "GetPixel" style calls).

But don't assume that that is all you need to do. The data itself might
have been encrypted and strewn around the image in a non-lineair pattern
(possibly even using a seeded random generator). It will make it rather
hard to find the bits themselves, and the order in which they should be
read.

In other words, steganography normally doesn't stop at layer #1. :-)

Regards,
Rudy Wieser

"J. P. Gilliver (John)" wrote:

For .jpg image files, I can add text notes to them very easily: in
IrfanView, I just (open the image and then) type I (info) then C
(comment).

This doesn't work for the .png file format.

_Does_ the .png format _have_ a metadata text field? If so, what utility
lets you see it, and ideally edit it?

(I'm talking about text that _becomes part of the file_, not that is
attached to it in some "album" type management system: such that it
remains part of the file even if the file is renamed, moved, or even
emailed.)

A decade or two ago I invested a lot of time using IrfanView's Comment
dialog to add info about many of my JPG photos. But occasionally I would
forgot that my other frequently used image editing program PaintShop Pro
8 unceremoniously destroyed them.
https://www.dropbox.com/s/uhsoy8hwu6...oyed.jpg?raw=1

(The much more recent version, PSP 2018, just deletes the comment
entirely.)

Similarly, PSP destroys any IPTC data.
https://www.dropbox.com/s/huwlfei503...oyed.jpg?raw=1

IV save options of course were set to preserve Comments, EXIF and IPTC:
https://www.dropbox.com/s/jr4zo7o5lb...ions.jpg?raw=1

PSP also lost original EXIF data, such as info important to me like GPS
coordinates etc.

I just took another look at Properties. The comment 'Test comment' I
added in IV does not appear using Win 10 FE R-click Properties.

But interestingly some of the test info I had added in the IPTC dialog
*does* appear. However, that doesn't include the caption description,
which could have been an alternative to Comment, unlike Author or
Copyright.
https://www.dropbox.com/s/f42it7l42d...ties.jpg?raw=1

Terry, East Grinstead, UK

In message , R.Wieser
writes:
John,

Can you explain in baby steps how you get to the "image properties -
summary dialog",

All I have to do, on XP, is to rightclick a file and select "properties"
from the popup menu.

I than get a dialog with two tabs, "General" and "Summary". Clicking the

Ah. I get five tabs - General, File Hashes, Security, Details, and
Previous Versions. (The File Hashes one is because of some utility I've
added that I think Paul put me onto.)

"Summary" tab gives me a "page" with a button at the bottom showing either
" Simple" or "Advanced ". When it shows "Advanced " the page above
it shows textboxes named, from the top, "Title", "Subject", "Author",
"Category", "Keywords" and "Comments".

But ... As you have W7 what you see might be rather different.

I was looking for an image to show you what I see, but could not find
anything better than the below. Just ignore the "Security" tab:

http://www.cs.mun.ca/jdk1.6/technote.../security2.gif

I'm not disbelieving you, just not sure where you're starting from.

From a different version of Windows than you are looking at. :-)

You might be looking at something like this:

https://www.sevenforums.com/attachme...80418003-file-
details-properties-add-change-remove-details-1.jpg

Yes, that's what I get (plus the File Hashes as mentioned above).

(notice the "comments" entry directly above the big, red, right-pointing
arrow)

Regards,
Rudy Wieser


I hadn't realised these were editable! The edit boxes don't appear until
you hover over them!

You can also edit them in the "details pane": in W7, an extra pane
appears across the Explorer window, beneath the folder tree pane on the
left and file list on the right. This pane can be enlarged (to show more
"details") by dragging its divider up. Again, I hadn't realised you
could edit in there!

However: although .jpg does indeed have a Comment field which can be
edited (either in Details under Properties, or in the details pane),
..png doesn't; it has a lot fewer details altogether, and the only
editable one is Date taken. (Do you see a comment field for a .png file
under XP?)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Cumulatively, however, they do get my goat, on my wick and up my nose, to the
extent I am angry enough to stick a wick up a goat's nose and to hell with the
consequences. - Eddie Mair, RT 2016/2/27-3/4

John,

I hadn't realised these were editable! The edit boxes don't appear until
you hover over them!

So much for GUI "improvements" I guess. :-)

Do you see a comment field for a .png file under XP?

Under XP the dialog itself doesn't change, it just grays out all fields that
it doesn't retrieve from the file. In the case of an PNG /all/ the fields
are grayed-out.

In other words, XP fully ignores the existance of those iTXt, tEXt, and
zTXt "chunks".

Regards,
Rudy Wieser

In message , Terry Pinnell
writes:
"J. P. Gilliver (John)" wrote:

For .jpg image files, I can add text notes to them very easily: in
IrfanView, I just (open the image and then) type I (info) then C
(comment).

This doesn't work for the .png file format.

_Does_ the .png format _have_ a metadata text field? If so, what utility
lets you see it, and ideally edit it?
[]
A decade or two ago I invested a lot of time using IrfanView's Comment
dialog to add info about many of my JPG photos. But occasionally I would
forgot that my other frequently used image editing program PaintShop Pro
8 unceremoniously destroyed them.
https://www.dropbox.com/s/uhsoy8hwu6...oyed.jpg?raw=1

(The much more recent version, PSP 2018, just deletes the comment
entirely.)

Similarly, PSP destroys any IPTC data.
https://www.dropbox.com/s/huwlfei503...oyed.jpg?raw=1

Clearly, the wonderful PSP is far from wonderful for any data other than
the pixels! I have heard of other utilities that don't retain some or
all fields, too. Since I use Irfan for all my image needs (I'm not sure
if I've even got any others installed on this machine - no, just
checked; three duplicate detectors, two EXIF editors, but no other
actual image manipulation), they're safe with me.

I think I've heard that the venerable Paint that comes as part of
Windows, has finally added other formats (than .bmp) in Windows 10; if
someone reading this has 10 and it does do .jpg, it'd be interesting to
know if _that_ changes/destroys .jpg comments.

IV save options of course were set to preserve Comments, EXIF and IPTC:
https://www.dropbox.com/s/jr4zo7o5lb...ions.jpg?raw=1

PSP also lost original EXIF data, such as info important to me like GPS
coordinates etc.

I just took another look at Properties. The comment 'Test comment' I
added in IV does not appear using Win 10 FE R-click Properties.

Nor here in W7. I just tried adding a comment in Explorer, and it
doesn't appear in Irfan's Comment box - but now, in the Irfan Properties
box, the EXIF info button has appeared, and the comment added _is_ there
under "XPComment" in that area. What's more, the Irfan comment is still
there - so at least Explorer doesn't destroy the other comment field,
unlike you tell us PSP does.

But interestingly some of the test info I had added in the IPTC dialog
*does* appear. However, that doesn't include the caption description,
which could have been an alternative to Comment, unlike Author or
Copyright.
https://www.dropbox.com/s/f42it7l42d...ties.jpg?raw=1

Terry, East Grinstead, UK

So .jpg files have at least three Comment spaces: as visible in Irfan,
there's the Comment button, but also under EXIF there's XPComment (which
appears not to be editable under Irfan!), and under IPTC there's
"Caption (description)" (which Irfan _can_ edit). In contrast, .png
doesn't appear to have any of them - but does have a field under EXIF
Pilot (under the EXIF tab).

I've just added comments using EXIF Pilot to a .jpg; it let me add them
under EXIF ad IPTC (but seems not to see the Irfan Comment field). Now
opening that file in Irfan: under EXIF, the comment is there - but under
"UserComment"; the one I added in Explorer is still there, under
"XPComment"! At least the IPTC one is in "Caption (description)".
And/but when I look in Explorer, _that_ now shows the comment I'd added
in EXIF Pilot, although the comment I'd added in Explorer previously is
still in the file as seen under Irfan. OK, I edited the comment in
Explorer, and looked in Irfan again - now (under EXIF) it shows the
comment I edited in Explorer under XPComment, but the UserComment field
has disappeared.

My brain hurts ... (-:
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Cumulatively, however, they do get my goat, on my wick and up my nose, to the
extent I am angry enough to stick a wick up a goat's nose and to hell with the
consequences. - Eddie Mair, RT 2016/2/27-3/4

On 14/02/2020 10:12, J. P. Gilliver (John) wrote:

In message , Terry Pinnell
writes:

Similarly, PSP destroys any IPTC data.
https://www.dropbox.com/s/huwlfei503...oyed.jpg?raw=1

Clearly, the wonderful PSP is far from wonderful for any data other than
the pixels!

I'm not aware of PSP doing that to anything of mine, but then that may
not mean much as, until this thread, I hadn't really bothered to
investigate things much - usually if I want to do anything like this,
it's to anonymise pictures which I plan to post on the internet, in
order to protect my privacy, such as where I live; in other words, I'm
just removing metadata rather than adding it.

However, *both* versions of PSP that I have freeze and crash; v6, which
is the only version that I have which works on W7 64-bit, fairly
frequently, v8, which works on XP 32-bit but not on W7 64-bit, only
quite rarely, so rarely that it is livable with - I wish the latter
would run on W7 64-bit.

I think I've heard that the venerable Paint that comes as part of
Windows, has finally added other formats (than .bmp) in Windows 10; if
someone reading this has 10 and it does do .jpg, it'd be interesting to
know if _that_ changes/destroys .jpg comments.

Paint will load and save PNG files, but know even less about them than
PSP, for example there is nothing under File, Properties to display any
image metadata.

Java Jive,

Paint will load and save PNG files, but know even less about them than
PSP, for example there is nothing under File, Properties to display any
image metadata.

Paint is an MS program. If the "file properties" dialog doesn't know about
PNG attributes, its very likely Paint won't either. :-)

And by the way: GDI+ (which contains the support for EXIF properties) does
not know how to write an EXIF property into a PNG image.

On the other hand, when using GDI+ to load a JPG image and saving it as a
PNG it does copy a JPG textrecord (id FFFE) into the PNG image as a "tEXt"
field, prepended a "Comment\0". They did not /fully/ throw their hats at
it.

Regards,
Rudy Wieser

GDI+ (which contains the support for EXIF properties) does not know how to
write an EXIF property into a PNG image.

That should ofcourse have read:

... does not know, under XP, how to ...

In message , R.Wieser
writes:
Java Jive,

Paint will load and save PNG files, but know even less about them than

Oh, only PNG? I'd thought maybe the W10 version did JPEGs by now.

PSP, for example there is nothing under File, Properties to display any
image metadata.

Paint is an MS program. If the "file properties" dialog doesn't know about
PNG attributes, its very likely Paint won't either. :-)

"File Properties" under 7 can edit _one_ PNG attribute, "Date taken".

And by the way: GDI+ (which contains the support for EXIF properties) does
not know how to write an EXIF property into a PNG image.

"EXIF Pilot" can; it _could_ be proprietary or a special, but it
presents it under an EXIF tab, _implying_ it's part of some standard.

On the other hand, when using GDI+ to load a JPG image and saving it as a
PNG it does copy a JPG textrecord (id FFFE) into the PNG image as a "tEXt"
field, prepended a "Comment\0". They did not /fully/ throw their hats at
it.

Regards,
Rudy Wieser


I've got a JPEG that, in IrfanView, has comment text (put there with
IrfanView), EXIF text (under the heading "XPComment"; put there with
Explorer [IrfanView can't _edit_ that, just view it]), and IPTC text.

When viewed in hex: the comment text starts at byte indexed as 06 (first
byte being indexed as 00); bytes 02 and 03 are FF and FE. The IPTC text
(in this file, anyway) starts at byte 00252C, where the preceding
sixteen bytes are 03 1B 25 47 1C 01 00 00 02 00 04 1C 02 78 00 08 (the
text I put there is 8 characters, so I guess that's that; I don't know
which if any of those byte pairs are a type identifier), and the EXIF
text starts at 001098 (stored with intervening zeroes, so possibly
001097 if they're leading zeroes), with many 00 bytes before it (so no
obvious data type identifier).
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

And indeed, Dutch isn't a lanuguage, it's a throat disease.
- Frank Slootweg in 3 Windows newsgroups, 2019-7-24

On 14/02/2020 13:52, J. P. Gilliver (John) wrote:
In message , R.Wieser
writes:
Java Jive,

Paint will load and save PNG files, but know even less about them than

Oh, only PNG? I'd thought maybe the W10 version did JPEGs by now.

Oh yes, I was taking that for granted! But it still doesn't have any
means of displaying, let alone altering, JPEG metadata.

John,

Oh, only PNG? I'd thought maybe the W10 version did JPEGs by now.

:-) Even under XP it can handle BMP, TIFF, GIF, JPG (several forms) and,
PNG.

"File Properties" under 7 can edit _one_ PNG attribute, "Date taken".

Less than usefull.

And by the way: GDI+ (which contains the support for EXIF properties) does
not know how to write an EXIF property into a PNG image.

"EXIF Pilot" can; it _could_ be proprietary or a special, but it presents
it under an EXIF tab, _implying_ it's part of some standard.

:-) When you use third-party programs all bets are off. Nothing stops a
program from putting or extracting an EXIF (or any other meta-data
containing) blob into/from one of the earlier mentioned PNG "chunks". Same
goes for other image formats ofcourse

As for "some standard" ? Yeah, I guess so. As long as that means "the
way that I (the program) did it" :-p

Regards,
Rudy Wieser