BUG: Summary Information reports incorrect JPEG resolution (300 instead of 72)

BUG: Summary Information reports incorrect JPEG resolution (300 instead of 72)

Post by Vince C » Fri, 06 Jun 2003 17:30:34



Hi all,

Sorry for multiposting. Pressed Send button too quickly.

I've displayed Summary Information for some JPG images which I know they are
72 DPI. Summary Information reports 300 DPI. Photoshop confirms actual
resolution is 72 DPI. Doubtlessly there is a bug here.

Vince C.

 
 
 

BUG: Summary Information reports incorrect JPEG resolution (300 instead of 72)

Post by Rick » Fri, 06 Jun 2003 19:10:08



> Hi all,

> Sorry for multiposting. Pressed Send button too quickly.

> I've displayed Summary Information for some JPG images which I know they are
> 72 DPI. Summary Information reports 300 DPI. Photoshop confirms actual
> resolution is 72 DPI. Doubtlessly there is a bug here.

This is horribly confusing, so please bear with me...

Windows reports whatever info is embedded in the Exif header
of a JPEG file.  Devices such as digital cameras and scanners use
arbitrary DPI numbers when writing JPEGs.  The numbers are
arbitrary because they aren't related to the image's actual resolution,
they're related to the intended output device.

For example, my 2 megapixel Canon A40 camera outputs JPEGs
with a DPI of "180" in the Exif header, while my 5 megapixel Sony
F717 writes "72" in the Exif header.  So Canon is assuming output
to an 180 DPI inkjet or laser printer while Sony is assuming output
to a monitor.  But the *actual* image resolution is completely
unrelated to *either* of these numbers.

Confused yet?  It gets worse.  Some graphics software such as
CorelPaint use DPI when specifying image resolution, while others
such as Photoshop use "pixels per inch", or PPI.  Again we're
dealing with the same thing -- the image resolution remains the
same, just the intended output device is different.  To convert one
to the other in Photoshop, go to Image/Image Size, uncheck the
"Resample Image" button and then enter your desired *print*
dimensions or resolution in the Document Size box.

RickW

 
 
 

BUG: Summary Information reports incorrect JPEG resolution (300 instead of 72)

Post by Vince C » Fri, 06 Jun 2003 22:16:16


Thanks, Rick.



[...]

Quote:> This is horribly confusing, so please bear with me...

Indeed :-)

Quote:> Windows reports whatever info is embedded in the Exif header
> of a JPEG file.  Devices such as digital cameras and scanners use
> arbitrary DPI numbers when writing JPEGs.  The numbers are
> arbitrary because they aren't related to the image's actual resolution,
> they're related to the intended output device.

> For example, my 2 megapixel Canon A40 camera outputs JPEGs
> with a DPI of "180" in the Exif header, while my 5 megapixel Sony
> F717 writes "72" in the Exif header.  So Canon is assuming output
> to an 180 DPI inkjet or laser printer while Sony is assuming output
> to a monitor.  But the *actual* image resolution is completely
> unrelated to *either* of these numbers.

> Confused yet?  It gets worse.  Some graphics software such as
> CorelPaint use DPI when specifying image resolution, while others
> such as Photoshop use "pixels per inch", or PPI.  Again we're
> dealing with the same thing -- the image resolution remains the
> same, just the intended output device is different.  To convert one
> to the other in Photoshop, go to Image/Image Size, uncheck the
> "Resample Image" button and then enter your desired *print*
> dimensions or resolution in the Document Size box.

> RickW

So if I understand, the information Windows displays in the Summary
Information has nothing to do with the actual image resolution - say - in
Photoshop? The reason is the information in the Exif header is intended for
a preferred display "engine" (printer or monitor).

My intention was in fact to know if the resolution we chose - say in
Photoshop - to create a JPG image has an impact on the filesize (considering
the same compression ratio).

Vince C.

 
 
 

BUG: Summary Information reports incorrect JPEG resolution (300 instead of 72)

Post by Rick » Fri, 06 Jun 2003 23:15:33



> Thanks, Rick.



> [...]
> > This is horribly confusing, so please bear with me...

> Indeed :-)

> > Windows reports whatever info is embedded in the Exif header
> > of a JPEG file.  Devices such as digital cameras and scanners use
> > arbitrary DPI numbers when writing JPEGs.  The numbers are
> > arbitrary because they aren't related to the image's actual resolution,
> > they're related to the intended output device.

> > For example, my 2 megapixel Canon A40 camera outputs JPEGs
> > with a DPI of "180" in the Exif header, while my 5 megapixel Sony
> > F717 writes "72" in the Exif header.  So Canon is assuming output
> > to an 180 DPI inkjet or laser printer while Sony is assuming output
> > to a monitor.  But the *actual* image resolution is completely
> > unrelated to *either* of these numbers.

> > Confused yet?  It gets worse.  Some graphics software such as
> > CorelPaint use DPI when specifying image resolution, while others
> > such as Photoshop use "pixels per inch", or PPI.  Again we're
> > dealing with the same thing -- the image resolution remains the
> > same, just the intended output device is different.  To convert one
> > to the other in Photoshop, go to Image/Image Size, uncheck the
> > "Resample Image" button and then enter your desired *print*
> > dimensions or resolution in the Document Size box.

> > RickW

> So if I understand, the information Windows displays in the Summary
> Information has nothing to do with the actual image resolution - say - in
> Photoshop? The reason is the information in the Exif header is intended for
> a preferred display "engine" (printer or monitor).

Yes.

Quote:> My intention was in fact to know if the resolution we chose - say in
> Photoshop - to create a JPG image has an impact on the filesize (considering
> the same compression ratio).

No, it doesn't.  You could choose 10000 PPI in Photoshop
and you'll still get the same filesize, but the image will print as
a tiny dot.  :-)

RickW

 
 
 

1. SSL Slows to a Halt after 48 to 72 hours

Looking for a possible fix to this problem.  I am running a secure website
on Win2K Server, SVCPK 1, IIS 5.  Host Headers are NOT being used on this
site.  It has its own IP address, TCP port 80 SSL port 443.

There are other sites on this box.  These ARE using Host Headers sharing a
DIFFERENT IP address.

After running quite well for 48 to 72 hours, SSL slows almost to a stand
still.  I've checked performance and resouorces are fine.  There are no
event log errors or application log errors.

Once I restart IIS services on the entire webserver, it seems to pick up
again.  Sometimes I have to restart IIS 2 or 3 times.

Here is the basic config:

Intel Pentium III 550 mhz
512 MB RAM
Windows 2000 Server
Service Pack 1
IIS 5
Certificate from Thawte Server CA
Secure site on its own IP address with NO host headers
SSL at port 443
NNTP and SMTP servers disabled
Other 10 Sites sharing a different IP address WITH host headers

Thanks,

David Felton

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9. Geting the 169.254.72.0 adress

10. Sys Summary Processor ID Incorrect

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12. File Summary tab information