A Windows XP help forum. PCbanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PCbanter forum » Microsoft Windows XP » General XP issues or comments
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

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



 
 
Thread Tools Display Modes
  #76  
Old February 17th 20, 09:30 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 17/02/2020 05:37, Paul wrote:

I tried this test too.

I was shocked to discover that PNG 0 was 70MB, PNG 1 (slight compression)
was 37MB, and PNG 9 (max compression) was 37MB. In other words, a picture
from a camera, there was only one level of lossless compression available
in a sense. It makes the compression level setting (almost) worthless.


PNG compression is a bit odd, the higher number doesn't always give the
best compression, though it usually does.
When I'm using a PNG on a website I often run it through optipng to find
the compression parameters that make the smallest file.
http://optipng.sourceforge.net/


The JPG it was made from was maybe 6-7MB or so. JPG can have quite high
compression, and the ratio of the sizes isn't that high of a compression
by JPG standards.


Don't forget you're comparing two very different things.
JPEG compression is lossy.
PNG and TIFF compressions are 100% lossless.


The secret weapon for JPG is the turbojpeg library. It uses
SSE, AVX, and/or multiple cores. And while there is IDCT
acceleration (inverse discrete cosine transform) available
from video cards, I don't know whether that fits into viewing
or not. When I tried JPG in Irfanview for example, it appeared
"instantly" on the screen.

Whereas for PNG, I doubt those sorts of acceleration are on offer.

One thing that was weird, was when I saved out a PNG with "zero"
compression, the output step was still slow.

And someone did think of parallelizing PNG compression. He views
it as the same problem as PIGZ (which is a parallelized GZIP compressor,
I think runs on two cores at least). Maybe the idea is to
break a PNG file down into multiple IDAT blocks, and do a
compression for each one on a different core. The blog entry
is from August 30, 2018.

https://brionv.com/log/2018/08/30/pa...-a-png-anyway/


It's amazing how slowly parallization passes into software lore.
Even PIGZ (a "prototype of parallelization") did not get picked up
in any substantial way. (I don't think Igor included that in 7ZIP
for example, only 7Z got accelerated.) If you want GZIP compression,
it's still largely a "single-core world".



Maybe it's just that good or best compression ratio sells both new
compression methods and new compression software. While parallelized
compression is usually a lot faster it doesn't quite compress as well as
a single threaded implementation, though typically it's close.

I use this archiver a lot and it can parallelize several of the most
intensive compression methods it supports: https://www.powerarchiver.com/

--
Brian Gregory (in England).
Ads
  #77  
Old February 17th 20, 09:38 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Andy Burns[_6_]
external usenet poster
 
Posts: 1,318
Default Image formats

Brian Gregory wrote:

Don't forget you're comparing two very different things.
JPEG compression is lossy.
PNG and TIFF compressions are 100% lossless.


TIFF files support various types of compression, including JPEG.
  #78  
Old February 17th 20, 09:42 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
nospam
external usenet poster
 
Posts: 4,718
Default Image formats

In article , Andy Burns
wrote:

Don't forget you're comparing two very different things.
JPEG compression is lossy.
PNG and TIFF compressions are 100% lossless.


TIFF files support various types of compression, including JPEG.


however, they're nearly always uncompressed.
  #79  
Old February 17th 20, 10:03 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Frank Slootweg
external usenet poster
 
Posts: 1,226
Default Image formats

Andy Burns wrote:
Brian Gregory wrote:

Don't forget you're comparing two very different things.
JPEG compression is lossy.
PNG and TIFF compressions are 100% lossless.


TIFF files support various types of compression, including JPEG.


The Wikipedia TIFF article lists the 'Usage and support' of JPEG
compression as 'Uncommon', so it's probably not wise to expect this to
work for most software.

'TIFF' (- '2.4 TIFF Compression Tag)
https://en.wikipedia.org/wiki/TIFF#TIFF_Compression_Tag

(FWIW, I happen to use TIFF with CCITT Group 4 fax encoding for
black-and-white scanned images of handwritten text. I don't remember if
my (Epson) scanner software defaulted to that format or that I got the
idea elsewhere.)
  #80  
Old February 17th 20, 10:23 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Big Al[_5_]
external usenet poster
 
Posts: 1,588
Default Image formats

On 2/17/20 3:30 PM, this is what Brian Gregory wrote:
On 17/02/2020 05:37, Paul wrote:

I tried this test too.

I was shocked to discover that PNG 0 was 70MB, PNG 1 (slight compression)
was 37MB, and PNG 9 (max compression) was 37MB. In other words, a picture
from a camera, there was only one level of lossless compression available
in a sense. It makes the compression level setting (almost) worthless.


PNG compression is a bit odd, the higher number doesn't always give the
best compression, though it usually does.
When I'm using a PNG on a website I often run it through optipng to find
the compression parameters that make the smallest file.
http://optipng.sourceforge.net/


The JPG it was made from was maybe 6-7MB or so. JPG can have quite high
compression, and the ratio of the sizes isn't that high of a compression
by JPG standards.


Don't forget you're comparing two very different things.
JPEG compression is lossy.
PNG and TIFF compressions are 100% lossless.


The secret weapon for JPG is the turbojpeg library. It uses
SSE, AVX, and/or multiple cores. And while there is IDCT
acceleration (inverse discrete cosine transform) available
from video cards, I don't know whether that fits into viewing
or not. When I tried JPG in Irfanview for example, it appeared
"instantly" on the screen.

Whereas for PNG, I doubt those sorts of acceleration are on offer.

One thing that was weird, was when I saved out a PNG with "zero"
compression, the output step was still slow.

And someone did think of parallelizing PNG compression. He views
it as the same problem as PIGZ (which is a parallelized GZIP compressor,
I think runs on two cores at least). Maybe the idea is to
break a PNG file down into multiple IDAT blocks, and do a
compression for each one on a different core. The blog entry
is from August 30, 2018.

https://brionv.com/log/2018/08/30/pa...-a-png-anyway/


It's amazing how slowly parallization passes into software lore.
Even PIGZ (a "prototype of parallelization") did not get picked up
in any substantial way. (I don't think Igor included that in 7ZIP
for example, only 7Z got accelerated.) If you want GZIP compression,
it's still largely a "single-core world".



Maybe it's just that good or best compression ratio sells both new
compression methods and new compression software. While parallelized
compression is usually a lot faster it doesn't quite compress as well as
a single threaded implementation, though typically it's close.

I use this archiver a lot and it can parallelize several of the most
intensive compression methods it supports: https://www.powerarchiver.com/

optipng doesn't change the image quality any? I've never used it, just
installed it on my system. I ran a test and some images were cut in
half. My eye doesn't see any quality diff.

Al

  #81  
Old February 17th 20, 10:48 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Mayayana
external usenet poster
 
Posts: 6,438
Default Image formats

"Big Al" wrote

| optipng doesn't change the image quality any? I've never used it, just
| installed it on my system. I ran a test and some images were cut in
| half. My eye doesn't see any quality diff.
|
Oh, that's easy. Just open your other eye.


  #82  
Old February 17th 20, 11:02 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Mayayana
external usenet poster
 
Posts: 6,438
Default Image formats

"Big Al" wrote

| optipng doesn't change the image quality any? I've never used it, just
| installed it on my system. I ran a test and some images were cut in
| half. My eye doesn't see any quality diff.
|

Informative piece he

http://optipng.sourceforge.net/pngtech/optipng.html

I just tried optipng on an existing 20.5 MB PNG image.
It took several minutes and reduced the size by only
a small bit. It says 2.57%.

The problem is that if you need to save those little
bits then you almost certainly don't want PNG in the
first place. JPG can be much smaller. Its lossy
compression is designed to drop out data that the human
eye is not likely to notice. So it can be greatly reduced
while still looking almost the same as the unaltered image,
as long as you don't need to enlarge it.


  #83  
Old February 18th 20, 03:26 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 17/02/2020 20:38, Andy Burns wrote:
Brian Gregory wrote:

Don't forget you're comparing two very different things.
JPEG compression is lossy.
PNG and TIFF compressions are 100% lossless.


TIFF files support various types of compression, including JPEG.


OMG.

TIFF seems like a nightmare compared to PNG.

--
Brian Gregory (in England).
  #84  
Old February 18th 20, 03:30 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 17/02/2020 22:02, Mayayana wrote:
The problem is that if you need to save those little
bits then you almost certainly don't want PNG in the
first place. JPG can be much smaller. Its lossy
compression is designed to drop out data that the human
eye is not likely to notice. So it can be greatly reduced
while still looking almost the same as the unaltered image,
as long as you don't need to enlarge it.


Depends what you're doing.
I wouldn't be wanting to reduce the size of a PNG for a website if it
was a photo, I'd use JPG. I'm not stupid.

On the other hand if the PNG was a graphic logo with a transparent
bvackground the PNG would probably be way smaller than a JPG which, er,
wouldn't have a transparent background WOULD IT?

--
Brian Gregory (in England).
  #85  
Old February 18th 20, 03:31 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 17/02/2020 21:48, Mayayana wrote:
"Big Al" wrote

| optipng doesn't change the image quality any? I've never used it, just
| installed it on my system. I ran a test and some images were cut in
| half. My eye doesn't see any quality diff.
|
Oh, that's easy. Just open your other eye.



Idiot.
It's all LOSSLESS compression.
Look it up.

--
Brian Gregory (in England).
  #86  
Old February 18th 20, 03:32 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 17/02/2020 21:23, Big Al wrote:
optipng doesn't change the image quality any?Â*Â* I've never used it, just
installed it on my system.Â* I ran a test and some images were cut in
half.Â* My eye doesn't see any quality diff.


No.
Just tries different lossless compression parameters to see what works
best for this particular file.


--
Brian Gregory (in England).
  #87  
Old February 18th 20, 04:43 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Mayayana
external usenet poster
 
Posts: 6,438
Default Image formats

"Brian Gregory" wrote

| | optipng doesn't change the image quality any? I've never used it,
just
| | installed it on my system. I ran a test and some images were cut in
| | half. My eye doesn't see any quality diff.
| |
| Oh, that's easy. Just open your other eye.
|
|
|
| Idiot.
| It's all LOSSLESS compression.
| Look it up.
|

Calm down. Just a joke. Are you on the payroll
of the International PNG Marketing Council, by any
chance?


  #88  
Old February 18th 20, 05:20 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 18/02/2020 15:43, Mayayana wrote:
Calm down. Just a joke. Are you on the payroll
of the International PNG Marketing Council, by any
chance?



You're the one who's insisting TIFF is best, claiming PNG is over
complicated when clearly TIFF is a way more complicated format.

--
Brian Gregory (in England).
  #89  
Old February 18th 20, 05:21 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Paul[_32_]
external usenet poster
 
Posts: 11,873
Default Image formats

Brian Gregory wrote:
On 17/02/2020 21:48, Mayayana wrote:
"Big Al" wrote

| optipng doesn't change the image quality any? I've never used it,
just
| installed it on my system. I ran a test and some images were cut in
| half. My eye doesn't see any quality diff.
|
Oh, that's easy. Just open your other eye.



Idiot.
It's all LOSSLESS compression.
Look it up.


I'm not sure that's true. Be careful there.

There are three levers.

1) DEFLATE compression. Lossless.
2) Pre-filter to (1) to improve compression performance.
Still lossless.
3) Palette reduction. Potentially lossy in the color domain.
If you start with a JPG with 100,000 false colors because
of math roundoff, then pass it through palette reduction,
the colors might get scrubbed down to 256 colors and
usage of the 8 bit palette. The difference between the
original set of colors and the new "256 approximate colors"
is a loss of some sort.

If you use pngcrush, it might be testing stuff like that
for you, and making a decision based on byte count.

Paul
  #90  
Old February 18th 20, 05:26 PM posted to alt.windows7.general,alt.comp.os.windows-10,microsoft.public.windowsxp.general
Brian Gregory[_2_]
external usenet poster
 
Posts: 166
Default Image formats

On 18/02/2020 16:21, Paul wrote:
...
There are three levers.

1) DEFLATE compression. Lossless.
2) Pre-filter to (1) to improve compression performance.
Â*Â* Still lossless.
3) Palette reduction. Potentially lossy in the color domain.
Â*Â* If you start with a JPG with 100,000 false colors because
Â*Â* of math roundoff, then pass it through palette reduction,
Â*Â* the colors might get scrubbed down to 256 colors and
Â*Â* usage of the 8 bit palette. The difference between the
Â*Â* original set of colors and the new "256 approximate colors"
Â*Â* is a loss of some sort.

If you use pngcrush, it might be testing stuff like that
for you, and making a decision based on byte count.

Â*Â* Paul


Nobody's even mentioned anything called pngcrush.

The program we're discussing is called optipng and it clearly says in
the first paragraph of it's website that no information is lost.

--
Brian Gregory (in England).
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off






All times are GMT +1. The time now is 09:09 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 PCbanter.
The comments are property of their posters.