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Definitely an encode/decode problem



 
 
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  #1  
Old September 1st 11, 10:09 PM posted to alt.binaries.pictures.astro
Skywise
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Posts: 318
Default Definitely an encode/decode problem

There must be something unique to this image that some programs
decode just fine but others have a problem. Unfortunately I don't
know enough about the jpg specification to know what the problem
is.

It could be that some programs jpg decompression routines are
faulty, and show the lines. Not all decoders are equal.

Yet, in my tests with really old software - my thumbnail viewer
dates back to 1999 or earlier - leads me to think the problem
is actually with Photoshop's encoding of the image.

The reason some viewers experience the lines while others don't
is because, again not all decoders are equal. Some may be failing
gracefully while others are adhering too strictly to the
specification and failing badly. Or it could be the other way
around - those that adhere strictly are OK, and it's the ones
that don't follow the rules correctly which fail.

The reason several programs may share the same problem viewing
the image is because they all import the same code library.

To test all this, somehow we'd have to do controlled tests of
encoding that TIFF to jpg with various programs, and viewing
all the results with more various programs.

How big is the TIFF file? I also have a recent version of PSP
on the other computer which can handle 16 bit TIFF's. I'm
wondering if that program's encoding to jpg would have any
issues.

Brian
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http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?
  #2  
Old September 2nd 11, 01:23 AM posted to alt.binaries.pictures.astro
Skywise
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Posts: 318
Default Definitely an encode/decode problem

Skywise wrote in news:NvS7q.44$4%.23
@newsfe18.ams2:

Yet, in my tests with really old software - my thumbnail viewer
dates back to 1999 or earlier - leads me to think the problem
is actually with Photoshop's encoding of the image.


I take that back. It's got to be in the decoding algorithm of
whatever is used to view the image.

I checked some of my own JPG's of varying sources, comparing them
to how they're displayed in Firefox. ALL of them display differently.

None show the stripes, but I think that may be because that
particular image just happens to have the right qualities to
evoke that. I've been reading a bit on how JPG works and the
stripes fit the 8x8 macroblock used in the compression scheme.

http://en.wikipedia.org/wiki/Jpg

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?
  #3  
Old September 3rd 11, 07:46 PM posted to alt.binaries.pictures.astro
Rick Johnson[_2_]
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Posts: 3,085
Default Definitely an encode/decode problem

On 9/1/2011 7:23 PM, Skywise wrote:
wrote in news:NvS7q.44$4%.23
@newsfe18.ams2:

Yet, in my tests with really old software - my thumbnail viewer
dates back to 1999 or earlier - leads me to think the problem
is actually with Photoshop's encoding of the image.


I take that back. It's got to be in the decoding algorithm of
whatever is used to view the image.

I checked some of my own JPG's of varying sources, comparing them
to how they're displayed in Firefox. ALL of them display differently.

None show the stripes, but I think that may be because that
particular image just happens to have the right qualities to
evoke that. I've been reading a bit on how JPG works and the
stripes fit the 8x8 macroblock used in the compression scheme.

http://en.wikipedia.org/wiki/Jpg

Brian

Thanks for all the work. I did try my not quite so ancient but just as
dangerous IE6 and got the lines. Yes, downloading the file (rather than
just copying the image as I foolishly tried) does show they are fine on
all my viewing programs. So it is a Firefox/Thunderbird decode issue.
Problem is many use those programs so I still need to avoid the issue.
It appears Thunderbird uses the same faulty decode even when I insert
the image rather than attach it. That allows me to see the lines before
it is sent. I'll have to remember to do that (only works in email mode
not Usenet) after this. I'm still using older versions of both. I've
not tried the latest version 6. I stuck with 3 (which is still
supported but not for long they say) since a couple plug-ins I use don't
work in the newer ones.

Rick


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  #4  
Old September 3rd 11, 11:41 PM posted to alt.binaries.pictures.astro
Skywise
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Posts: 318
Default Definitely an encode/decode problem

Rick Johnson wrote in news:4e6275ee$0$2996$a8266bb1
@newsreader.readnews.com:

Thanks for all the work.


No problem. I really wish I could take the time and/or focus more
on my programming and become familiar with the vagaries of image
formats. The reason I delved into the TIFF specification was due
to a problem I was having with some USGS data, which was in an
extension of TIFF called GeoTIFF (needed to eliminate some data
stored in the alpha channel). And then when we find a little
problem like this with JPG's, it makes me wish I knew more.



I did try my not quite so ancient but just as
dangerous IE6 and got the lines.


Interesting. I used IE5 and had no lines. So we know when the
change happened.

Although, a possibility, is that it's not IE itself, but the
windows system libraries that decode JPG's. I don't know if that's
how it's done, though. Again, I don't know enough. I do know
enough programming to be amazed that anything as complex as
today's software and operating systems can even be done at all.


Problem is many use those programs so I still need to avoid the issue.


A suggestion, a disclaimer? For example, if I had these images on
a website, I'd make a note about possible display problems caused
by some software. For most images it appears to be unnoticeable,
but for these astropics it seems to be more of an issue.

This issue has me curious enough that I would like to spend some
more time delving into the issue. I have done some my last post
and I have seen some discussion online about this problem, but I
haven't been able to nail down exactly what may be causing it. I
might have to sneak into the Firefox user forums and post a note
about it. They might appreciate it if it turns out to be a bug
that no one noticed before.


It appears Thunderbird uses the same faulty decode


I only use thunderbird for email. I use XNews for usenet. But I
might email myself a test pic or two to see what happens.


I'm still using older versions of both. I've
not tried the latest version 6.


I tend to stay with older software myself for various reasons even
though I may have more current hardware. For example, I'm using
Win2Kpro and XPpro on my two Core2 systems. I believe in the old
dictum, "If it ain't broke, why fix it?" Yeah, there are some things
that I do go for the new stuff. When I snagged PaintShopPro, I got
the latest and greatest available at that time (can't justify the
cost of Photoshop just yet). Same for my audio editing soft and
hardware (Adobe Audition 3.0/Echo Layla 3G), but then I'm pretty
serious about my (amateur) music.

But I'm 'afeared' of MS's offerings past XP, and these OS's are
starting to show their age too much. So I'm exploring other options.
In fact, as I write this, I'm burning a Kubuntu Linux distro CD to
try out.

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?
 




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