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



 
 
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  #1  
Old February 13th 20, 11:59 AM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
J. P. Gilliver (John)[_7_]
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Posts: 603
Default Does the .png image format have a text metadata field?

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

Science isn't about being right every time, or even most of the time. It is
about being more right over time and fixing what it got wrong.
- Scott Adams, 2015-2-2
  #2  
Old February 13th 20, 12:30 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Java Jive
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Posts: 391
Default Does the .png image format have a text metadata field?

On 13/02/2020 10:59, 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.)


I think it depends not just on whether the Portable Network Graphics
format can contain metadata, but also whether you want the metadata to
be available under, say, File or rt-click, Properties, Details in
Explorer. The answer to the first seems to be yes, the second seems to
be no. As a test I have just added some information to a *.png file
using Paint Shop Pro, and it is remembered if the program is closed and
then reopened and the same file loaded, and examination of the binary
contents of the file shows the strings added to be there. However, they
are not shown by the default Windows Image Viewer program, nor under the
File, Properties in Explorer.
  #3  
Old February 13th 20, 01:02 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
R.Wieser
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Posts: 1,302
Default Does the .png image format have a text metadata field?

John,

_Does_ the .png format _have_ a metadata text field?


Yes. The below document describes the iTXt, tEXt, and zTXt "chukns", which
can be used to store such data.

https://dev.exiv2.org/projects/exiv2...a_in_PNG_files

If so, what utility lets you see it, and ideally edit it?


I'm sorry, but I have absolutily no idea. Depending on your version of
Windows you might be able to add/edit them using :

rightclick on the image - properties - summary

(Doesn't work under XP)

If not, try a google for "png edit exif" (EXIF is a kinda metadata
standard).

Regards,
Rudy Wieser


  #4  
Old February 13th 20, 01:49 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
J. P. Gilliver (John)[_7_]
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Posts: 603
Default Does the .png image format have a text metadata field?

In message , R.Wieser
writes:
John,

_Does_ the .png format _have_ a metadata text field?


Yes. The below document describes the iTXt, tEXt, and zTXt "chukns", which
can be used to store such data.

https://dev.exiv2.org/projects/exiv2...a_in_PNG_files


Thanks. You, Java Jive, and Paul have confirmed that.

If so, what utility lets you see it, and ideally edit it?


I'm sorry, but I have absolutily no idea. Depending on your version of
Windows you might be able to add/edit them using :

rightclick on the image - properties - summary

(Doesn't work under XP)


Nor 7 (there is no "summary" tab [or even a "Summary" one]).

Java Jive said he used Paint Shop Pro to add some "information" to a
..png, and since he said he found the "strings" in the file afterwards, I
presume he meant text. I think I have PSP somewhere (IIRR even a Big
Version they made available when they wanted to close down servers or
something, though that may be something else), but it seems a bit of a
sledgehammer to load it just for this.

If not, try a google for "png edit exif" (EXIF is a kinda metadata
standard).

Regards,
Rudy Wieser


I'm just doing that. www.thexifer.net seems to be a web-based one.
ExifTool is a command line one, though there are GUI ones that use it.
Exif Pilot (https://www.colorpilot.com/exif.html) looks promising and
small (and free), and claims to do .png ... Trying: yes, seems to work.
(There's a "Comment" field. From the layout - it's a single line - there
might well be a size limit, and I suspect it won't allow line feeds.)

Had a term in the licence I haven't seen befo something like "you may
not use previous versions". I poked around in it and couldn't see any
mention of updates, but that doesn't mean it doesn't automatically get
them. (For the rare times I'm likely to use it, I CBA to be bothered.)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"Gentlemen, you can't fight in he this is the war room!" (Dr. Strangelove)
  #5  
Old February 13th 20, 02:24 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
R.Wieser
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Posts: 1,302
Default Does the .png image format have a text metadata field?

John,

Java Jive said he used Paint Shop Pro to add some "information" to a .png,


/Any/ program can use those those "chunks" (and not"chukns" :-) ) to store
(textual, meta) data into. And thats the whole problem.

You can put a bit of text in there, but the moment you want to store
multiple pieces of information (name and date to name two) the way to
identify and seperate those pieces is fully upto the person who (or program
which) adds the metatdata, as there is no specification for it.

You can ofcourse decide use a program that puts an EXIF formatted metadata
block into them, but that needs its own not-as-simple parsing and doesn't
offer fields you can name yourself.

Yep, you're stuck between a rock and a hard place. :-)

Regards,
Rudy Wieser


  #6  
Old February 13th 20, 02:41 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
J. P. Gilliver (John)[_7_]
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Posts: 603
Default Does the .png image format have a text metadata field?

In message , R.Wieser
writes:
John,

Java Jive said he used Paint Shop Pro to add some "information" to a .png,


/Any/ program can use those those "chunks" (and not"chukns" :-) ) to store
(textual, meta) data into. And thats the whole problem.

You can put a bit of text in there, but the moment you want to store
multiple pieces of information (name and date to name two) the way to
identify and seperate those pieces is fully upto the person who (or program
which) adds the metatdata, as there is no specification for it.

You can ofcourse decide use a program that puts an EXIF formatted metadata
block into them, but that needs its own not-as-simple parsing and doesn't
offer fields you can name yourself.

Yep, you're stuck between a rock and a hard place. :-)

Regards,
Rudy Wieser

Not really; I only wanted a free-form text area (a "Comment" field if
you like). Exif Pilot does seem to give me that - _and_ fixed fields for
assorted dates, and other things, which _implies_ that those are in fact
set down in the format. Are you saying they're not?

Is there a general format for an EXIF "block", which the various image
file formats - .jpg, .png, etc.- just form a "wrapper" for? I had
assumed not, i. e. that each image file format had its own (some
optional) blocks, at least for things like photograph details (camera
model, date taken, lens and "film" settings, shutter speed, and so on).

2
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Hadrian's Wall has never been a border between Scotland and England. It lies
entirely within England but, when it was built in AD 122 by the Romans as a
defence against the raiding Picts, the future English were still in Germany
and the Scottish were still in Ireland.
- Michael Cullen, Skye, in RT 2014/12/6-12
  #7  
Old February 13th 20, 03:14 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Mayayana
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Posts: 6,438
Default Does the .png image format have a text metadata field?

"J. P. Gilliver (John)" wrote

| Not really; I only wanted a free-form text area (a "Comment" field if
| you like). Exif Pilot does seem to give me that - _and_ fixed fields for
| assorted dates, and other things, which _implies_ that those are in fact
| set down in the format. Are you saying they're not?
|
| Is there a general format for an EXIF "block", which the various image
| file formats - .jpg, .png, etc.- just form a "wrapper" for? I had
| assumed not, i. e. that each image file format had its own (some
| optional) blocks, at least for things like photograph details (camera
| model, date taken, lens and "film" settings, shutter speed, and so on).

Each format is entirely different. Embedded metadata is mainly the
invention of Adobe. Then it was useful and became standardized
through use. But it's still not entirely standard. And EXIF data is not
required for the format. Meanwhile, everyone and his brother have
made up their own tags. Microsoft even created tags with unicode
strings, breaking the rule everyone else follows. But it's their
tag and it's an open standard. So whether this stuff is official
depends mostly on how many people use it.

JPG metadata is popular mainly because people want to tag
their photos from Sally's wedding, and because journalists want
to infest their photos with official copyright data, not realizing
that data is not actually part of the image data but only an
optional addition to the file header that can be easily removed.

In general, file formats include a header and data. The header
IDs the file type and can include a lot more info in some cases.
But the only required parts are the parts that allow the file data
to be interpreted as intended.

These image files are raster images, which means they're all
bitmaps. All of them store data that can be unpacked to provide
a gridwork of pixel values in order to render the image. A BMP
is little more that that data in a long string. You could actually
count down into the file, if you wanted to, to find the RGB pixel
values of the pixel at 300,400 offset from the top right corner.

A TIF is usually just a BMP that's been zipped. GIF, JPG, PNG all
use different methods to compress the data and all have unique
pros and cons. But they're all ways to package a bitmap.

If you look at the link you'll see a PNG is somewhat unusual. The
header, such as it is, is only a few bytes IDing the file type. What's
usually called the "file magic". The rest is blocks of data with identifying
bytes. PNGs also come in a large number of types. It's a very
complex format. And since there's no simple rule for putting metadata
in a header, as there is for JPG, it's a more difficult task.


  #8  
Old February 13th 20, 03:21 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
R.Wieser
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Posts: 1,302
Default Does the .png image format have a text metadata field?

John,

Not really; I only wanted a free-form text area (a "Comment" field if you
like).


Than you are home-free as they say. :-)

Exif Pilot does seem to give me that - _and_ fixed fields for assorted
dates, and other things, which _implies_ that those are in fact set down
in the format. Are you saying they're not?


No, I tried to say that you can use every field EXIF offers, but if you
would want to add a, for example, "Comments_two" field you would be
out-of-luck.

The "character size" of an EXIF field is bound to its (numeric) type. You
could introduce a new type, but if some other program isn't aware of that
new type (and thus can't look-up the "character size") it will break its
parsing of the EXEF datablob (as you do not know where the next field
starts).

Is there a general format for an EXIF "block",


Yes.

which the various image file formats - .jpg, .png, etc.- just form a
"wrapper" for?


No.

Though, as mentioned, you can put an EXIF blob into an "put anything you
wish here" free-form field - /if/ the image format offers it. Don't
expect, for example, the venarable BMP format to have it.

I had assumed not, i. e. that each image file format had its own (some
optional) blocks,


The newer image formats often have such an optional free-to-use block, the
older ones not. Though IIRC the "newer" DDS image format doesn't have one
either.

at least for things like photograph details (camera model, date taken,
lens and "film" settings, shutter speed, and so on).


Definitily not that, as quite a number of image formats had/have no
connection whatsoever with a camera. PNG is one of those.

Regards,
Rudy Wieser


  #9  
Old February 13th 20, 02:33 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Paul[_32_]
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Posts: 11,873
Default Does the .png image format have a text metadata field?

J. P. Gilliver (John) wrote:
In message , R.Wieser
writes:
John,

_Does_ the .png format _have_ a metadata text field?


Yes. The below document describes the iTXt, tEXt, and zTXt "chukns",
which
can be used to store such data.

https://dev.exiv2.org/projects/exiv2...a_in_PNG_files


Thanks. You, Java Jive, and Paul have confirmed that.

If so, what utility lets you see it, and ideally edit it?


I'm sorry, but I have absolutily no idea. Depending on your version of
Windows you might be able to add/edit them using :

rightclick on the image - properties - summary

(Doesn't work under XP)


Nor 7 (there is no "summary" tab [or even a "Summary" one]).

Java Jive said he used Paint Shop Pro to add some "information" to a
.png, and since he said he found the "strings" in the file afterwards, I
presume he meant text. I think I have PSP somewhere (IIRR even a Big
Version they made available when they wanted to close down servers or
something, though that may be something else), but it seems a bit of a
sledgehammer to load it just for this.

If not, try a google for "png edit exif" (EXIF is a kinda metadata
standard).

Regards,
Rudy Wieser


I'm just doing that. www.thexifer.net seems to be a web-based one.
ExifTool is a command line one, though there are GUI ones that use it.
Exif Pilot (https://www.colorpilot.com/exif.html) looks promising and
small (and free), and claims to do .png ... Trying: yes, seems to work.
(There's a "Comment" field. From the layout - it's a single line - there
might well be a size limit, and I suspect it won't allow line feeds.)

Had a term in the licence I haven't seen befo something like "you may
not use previous versions". I poked around in it and couldn't see any
mention of updates, but that doesn't mean it doesn't automatically get
them. (For the rare times I'm likely to use it, I CBA to be bothered.)


This is a sample image with old-style metadata in a PNG.

https://i.stack.imgur.com/UiagX.png

identify -verbose UiagX.png

Properties:
Author: Hans Müller
Date: 2010-12-08 09:45
date:create: 2010-12-08T13:15:43+01:00
date:modify: 2010-12-08T13:15:43+01:00
Desc: A long time ago in a galaxy far far away....
signatu 3b4a54202316a7ae4b4fe0e431d47958181f4bb89349335582 0d4ba74f9f5ee3

It's possible the Desc is the "Comment" capability.

I could also find a reference to "tools doing naughty things",
such as taking EXIF data and stuffing it into old-style metadata
carriage.

This just makes it harder for other tools to do a good
job on incoming files.

There are supposed to be sample files with the EXIF proposal
for PNG, but I couldn't find them.

Adding a comment to the file might be easier than adding
a clutch of standard EXIF values. In theory, adding EXIF
values would be better for federated search indexing,
but you know how sketchy Windows support is for that
stuff anyway (only "standard" EXIF fields are indexed).

*******

https://en.wikipedia.org/wiki/ExifTool

https://exiftool.org/

ExifTool is also available as a stand-alone Windows executable:

(Note that these versions contain the executable only, and do
not include the HTML documentation or other files of the
full distribution above.)

Windows Executable: exiftool-11.86.zip (6.2 MB)

The stand-alone Windows executable does not require Perl.

Just download and un-zip the archive then double-click on
"exiftool(-k).exe" to read the application documentation,
drag-and-drop files and folders to view meta information,
or rename to "exiftool.exe" for command-line use. Runs on
all versions of Windows.

(Note: Oliver Betz provides an alternate ExifTool Windows
installer that avoids some problems of the self-extracting
archive version above)

That sounds like fun :-/

Paul
  #10  
Old February 13th 20, 02:54 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Mayayana
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Posts: 6,438
Default Does the .png image format have a text metadata field?

"J. P. Gilliver (John)" wrote

| Java Jive said he used Paint Shop Pro to add some "information" to a
| .png, and since he said he found the "strings" in the file afterwards, I
| presume he meant text. I think I have PSP somewhere (IIRR even a Big
| Version they made available when they wanted to close down servers or
| something, though that may be something else), but it seems a bit of a
| sledgehammer to load it just for this.

It seems to be like JPG of 20 years ago. As others have said,
there are accommodations for metadata strings in the file
format, but that doesn't make it standard. I just tried a PNG
with metadata in IrfanView. It didn't see the data. But actually,
this PNG doesn't have data as such. It only has the labels,
like Author, Description, etc. A second file has no labels.

I'm surprised you care about this. I have a hard time even
finding a PNG on my drives. The only ones I have are charts
that I downloaded from webpages. Few suites use them because
they're big. A JPG can show a photo image much smaller. A
GIF can show a chart much smaller. I really don't understand
why anyone uses PNG online. One could use PNG for compressed
images on disk, but for that there's TIF.

I have PSP 5 and 16. The former doesn't recognize JPG EXIF
data. The latter saves it. I prefer the former. But ever since
people started taking photos of everything with their phones,
there's a big call for JPG metadata standardization. That won't
happen with PNG unless there's a call for that. Which would
probably require that PNG become the standard for low quality
cellphone/camera photos. PNG is better in being lossless. But
PNG also takes up more space, so that might not happen. When
photos are just for sending between phones, quality doesn't
matter much.


  #11  
Old February 13th 20, 04:26 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Java Jive
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Posts: 391
Default Does the .png image format have a text metadata field?

On 13/02/2020 13:54, Mayayana wrote:

"J. P. Gilliver (John)" wrote

| Java Jive said he used Paint Shop Pro to add some "information" to a
| .png, and since he said he found the "strings" in the file afterwards, I
| presume he meant text. I think I have PSP somewhere (IIRR even a Big
| Version they made available when they wanted to close down servers or
| something, though that may be something else), but it seems a bit of a
| sledgehammer to load it just for this.


Yes, I added two strings into two of the four fields offered under View,
Image Information, Creator Information, (but the menu path is probably
different in different versions of PSP) which are ...
Image Title I put something here
Artist Name
Copyright
Description I put something else here
.... and I could see the results in a hexadecimal disply of the image
file, but, as already indicated, not in Windows File Explorer or Windows
Image Viewer (W7 HP versions).

I'm surprised you care about this. I have a hard time even
finding a PNG on my drives. The only ones I have are charts
that I downloaded from webpages. Few suites use them because
they're big. A JPG can show a photo image much smaller. A
GIF can show a chart much smaller.


As you indicated further on in a part I snipped because I've nothing
further to add to it, the difference is in the compression: PNG is a
lossless format, others such a JPEG are lossy, and the difference can be
important. So, for example, it used to be that BBC used JPEGs for their
images in their news pages, but they were so compressed to hell that you
couldn't actually see much in them, and if they were graphs, forget
trying to read the legend or the scales! Haven't had cause to examine
one closely recently, so don't know what their current standards are.
For this reason, when I put something up on my site where detail is
important, invariably I use PNG.

As some here, and in some other ngs, may know and recall, over the last
year or so I have scanned my way through a trunk full of ancient
Macfarlane documents that have come down through my family over many
generations, some of them so old as even to be parchments on animal
skin. I have use PNGs exclusively for this work, and in fact use them
almost universally for anything that I produce.

I really don't understand
why anyone uses PNG online. One could use PNG for compressed
images on disk, but for that there's TIF.


TIFF files are *MUCH* bigger than PNG, for example 22.1Mb as opposed to
8.24MB for the same picture.
  #12  
Old February 14th 20, 01:12 AM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Mayayana
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Posts: 6,438
Default Does the .png image format have a text metadata field?

"Java Jive" wrote

| TIFF files are *MUCH* bigger than PNG, for example 22.1Mb as opposed to
| 8.24MB for the same picture.

It sounds like you have a lot more experience than I do,
but I don't see that. A TIF is basically a zipped BMP. I
just tried converting a 252 KB PNG to TIF and got 217 KB.
Then I tried saving a 5 MB JPG image with IrfanView
(52 MB BMP). 4 MB for the TIF. 21 MB for the PNG. That's
with compression level 6 and no transparency color. Though
I assume PNG has to save the alpha channel anyway.
So no advantage there.


  #13  
Old February 13th 20, 07:03 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
J. P. Gilliver (John)[_7_]
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Posts: 603
Default Does the .png image format have a text metadata field?

In message , Mayayana
writes:
[]
format, but that doesn't make it standard. I just tried a PNG
with metadata in IrfanView. It didn't see the data. But actually,
this PNG doesn't have data as such. It only has the labels,
like Author, Description, etc. A second file has no labels.


Seems the format _can_ have these fields; I don't know if that means
_every_ .png _does_ have them. (In the same way a JPG _can_ have both
EXIF and Comments, but doesn't _have_ to; in IrfanView, whether it does
is shown by the presence or absence of asterisks on the EXIF and comment
buttons.) It seems IrfanView doesn't yet know about the _possibility_ of
these fields in the .png format, though.

I'm surprised you care about this. I have a hard time even
finding a PNG on my drives. The only ones I have are charts
that I downloaded from webpages. Few suites use them because
they're big. A JPG can show a photo image much smaller. A
GIF can show a chart much smaller. I really don't understand
why anyone uses PNG online. One could use PNG for compressed
images on disk, but for that there's TIF.


I don't originate in it, but as you say, sometimes downloads come in it
- and I don't like to do needless format conversions.

I have PSP 5 and 16. The former doesn't recognize JPG EXIF
data. The latter saves it. I prefer the former. But ever since


I had 5 and 7 - I think way back on my '98SElite machine. I preferred 5
- the only reason I ever used 7 was the odd image that was too big for 5

people started taking photos of everything with their phones,
there's a big call for JPG metadata standardization. That won't
happen with PNG unless there's a call for that. Which would
probably require that PNG become the standard for low quality
cellphone/camera photos. PNG is better in being lossless. But
PNG also takes up more space, so that might not happen. When
photos are just for sending between phones, quality doesn't
matter much.


2
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

You can believe it if it helps you to sleep. - Quoted by Tom Lehrer (on
religion, in passing), April 2013.
  #14  
Old February 13th 20, 07:39 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
R.Wieser
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Posts: 1,302
Default Does the .png image format have a text metadata field?

John

In the same way a JPG _can_ have both EXIF and Comments, but doesn't
_have_ to;


Are you sure about that ?

The last time I edited the EXIF information in a JPG image using the
"properties" dialog Windows has the "Comments" that I had also put in there
where hoovered into the EXIF block. Definitily not what I expected or
wanted.

Or, in other words: You can put them in there, but its easy to lose the
non-EXIF comment(s).

Regards,
Rudy Wieser


  #15  
Old February 13th 20, 01:03 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Paul[_32_]
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Posts: 11,873
Default Does the .png image format have a text metadata field?

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.)


It has multiple flavors of metadata, according to this.

https://stackoverflow.com/questions/...-data-like-jpg

The original specification has two kinds of text chunks,
a plaintext and a compressed text thing. And also has some other
things which contain specific kinds of information.

https://en.wikipedia.org/wiki/Portable_Network_Graphics

"ancillary chunks"

The above (temporally long) StackOverflow claims in 2017, an
actual EXIF chunk was added. The benefit of this, is
no "custom" handler would be needed to attempt to parse
key-value pairs from one of the older chunk types. Since this
is optional, no program absolutely has to add it, and the
usual 4CC parse logic applies (a field you don't understand,
ignore it).

http://ftp-osl.osuosl.org/pub/libpng....0.html#C.eXIf

[4CC code of "eXIf" case sensitive]

As of today then, you can add it.

It's just a matter of "tools" to do it.

Note that the idea of compressing text means that you
can't just necessarily dump the old chunk style into
a hex editor and "recognize" the text by eye. Only the
weakest kinds of compression (like LZ4) allow doing that.

Whereas, at a guess, if an EXIF chunk was added, I would
expect the EXIF chunk to be similar to other image formats,
and concentrate more on usability than efficiency. If we
could find an example of a 2017+ PNG with added EXIF, then
we could check for that.

But otherwise, PNG has a lot of emphasis on efficiency.
That's why one PNG program, it attempts to compress a
PNG like 20 times (with different settings), it compares
all the compressed sizes, then "picks" the smallest file
out of the lot. PNG has multiple bit-depth settings,
which allow cartoon-like materials to be heavily compressed.

For some reason, the program for doing that can't seem to
just pick the best options from an analysis of the format,
and relies on brute force compression followed by
selection, to pick the format. People use such programs
for web site preparation and crushing the byte count
for best efficiency. Like it matters when the .js fleet
is 5MB :-( "The part that pays the bills", they don't
care how big that part gets. Whereas the PNG file must
be crushed flat.

So if you were expecting to see a lot of metadata in
web page PNGs, I would guess it wouldn't be that common.
It would take a JPG camera picture, a workflow with
2017 extension support, followed by presentation of
the item by an amateur somewhere.

In a quick search, the PNGs in my current download folder,
none of those seemed to have anything resembling an EXIF.
But that doesn't mean anything. Whereas if I were to
start throwing downloaded JPG images into HxD, I would
likely be seeing some text up near the front (an occasional
JPG would still have the camera data).

Summary: Yes, you can add metadata.
Problem one, is adding the new chunk type.
Problem two, is a recipient being able to view the
new added chunk.
Problem three, is downloading a recent enough tool,
so that JPG to PNG conversion, conserves the EXIF part,
so you won't be doing this by hand.

I doubt I have anything like that here, since I would never
have expected an image format to evolve, and then me
needing to upgrade tools for that specific purpose.
Imagemagick is probably the tool I would be most likely
to sample a new version. GIMP, the "playing with the interface
crap", has driven me away from trying new versions. While I have
Irfanview on a number of OS installs here, I don't spend a lot
of time in that program to know when support for that would
be added.

For these newsgroups then, the question would be whether
the federated search has a handler for EXIF in PNG and
indexes it, or has an option to display an EXIF chunk if you
manage to add one. I presume you want integration so
the OS does something useful too.

If the 2017 date is correct, I wouldn't expect miracles. Even
Windows 10 might be missing support.

Paul
 




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