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From: Catch up - you fuckin' morons on 5 Apr 2010 22:45
On 06 Apr 2010 02:42:37 GMT, rfischer(a)sonic.net (Ray Fischer) wrote:

>Tim <timmorr64(a)XremoveXhotmail.com> wrote:
>>Elmo wrote:
>
>>> Assumption: You want to automatically rotate, shrink to 100KB, set to
>>> 72dpi, strip out the EXIF data, and rename the new emailable files
>>> based on the EXIF date & EXIF gps coordinates for all photographs in
>>> a Windows folder.
>>
>>Why are you setting the resolution to 72 pixels per inch? If they are to be
>>emailed and viewed on screen the resolution doesn't matter at all, if they
>>are to be printed then 72 ppi is way too low.
>
>Does _anything_ pay attention to the DPI setting?

Advanced editors that give a real-time preview option for the print output
do. Like Photoline. It will even show you the printer's eventual
anti-aliasing quality before you even send it to the printer, if you so
desire.



From: Tim on 6 Apr 2010 06:43
Elmo wrote:
> On Tue, 6 Apr 2010 11:02:22 +1000, Tim wrote:
>
>>> Assumption: You want to automatically rotate, shrink to 100KB, set
>>> to 72dpi, strip out the EXIF data, and rename the new emailable
>>> files
>> Why are you setting the resolution to 72 pixels per inch? If they
>> are to be emailed and viewed on screen the resolution doesn't matter
>> at all
>
> Good question!
>
> I thought reducing the DPI from whatever it is from the camera down
> to 72 DPI lowered the file size (in bytes on disk).
>
> Can you clarify the relationship of DPI with bytes on disk?
>
> Assuming two photographs are exactly the same, except one is 72 DPI
> and the other is, say, 1,200 DPI, wouldn't one would be vastly larger
> in file size (bytes on disk) than the other?
>
> If the answer is Yes, then that's why I recommend 72DPI for emailed
> photos. If the answer is No, then ... you're right ... it's a waste
> of time to set the DPI in Irfanview Batch Mode.
>
> What is the right answer to recommend to batch shrink common photos
> to be emailed?

There will be absolutely no difference in file size. The only difference
will be a few bytes in the file header that read will 72 in one image and
1200 in the other. The part of the image that contains the image
information will be identical.
As an example, here are two images. Both are 800 x 600 pixel JPGs that were
saved with the same settings for compression, but one has a resolution of 72
ppi and the other is 1200 ppi. Both have a file size of 95,277 bytes.
http://www.fileden.com/files/2008/6/28/1979560/Res72.jpg
http://www.fileden.com/files/2008/6/28/1979560/Res1200.jpg

Resolution is only applicable to printed images, or applications that show
your image on a virtual piece of paper. Something like a word processor, a
desktop publishing application or something with "print preview". This
doesn't apply to web browsers, email programs, image viewers or image
editors (in their normal mode).
If you have an image that is 3600 x 2400 pixels and it has a resolution of
1200 pixels per inch, it will print at a size of 3 inches by 2 inches. If
you change the resolution to 600 pixels per inch it will print at a size of
6 inches by 4 inches. That's all resolution means... a conversion factor
from "pixels", which have no fixed size, to a physical measurement such as
inches. It doesn't mean that each pixel contains more information at higher
resolution. A pixel just contains the colour of one dot. Resolution doesn't
mean the same as the resolving power of a lens.
A good page about all of this is http://www.scantips.com/no72dpi.html

--
Tim


From: Elmo on 6 Apr 2010 13:35
On Tue, 06 Apr 2010 08:35:37 -0700, Paul Furman wrote:

> Setting 72 ppi ... [will] cause it to print by default at a size similar to what
> you see on screen, where a 300 ppi setting would come out of the printer
> at postage stamp size, but it has no effect on file size on disk.

Interesting.

Ummm... so what PPI/DPI settings SHOULD we recommend for batch shrinking
and renaming suitable for emailing family photos to others?

300?
600?
1200?
?
From: me on 6 Apr 2010 15:37
On Tue, 06 Apr 2010 08:35:37 -0700, Paul Furman <paul-@-edgehill.net>
wrote:

>Setting 72 ppi could be useful if people want to print a low res web
>image; that'll cause it to print by default at a size similar to what
>you see on screen, where a 300 ppi setting would come out of the printer
>at postage stamp size, but it has no effect on file size on disk.

That implies a fair amount of assumption about the
application/feature/driver set up used to print he photo, doesn't it?

html browser vs image viewer vs image editor vs image printing app.
From: Chris Malcolm on 6 Apr 2010 18:31
In rec.photo.digital Elmo <dcdraftworks(a)use-author-supplied-address.invalid> wrote:
> On Tue, 6 Apr 2010 10:49:22 +1000, Tim wrote:

>> Which is exactly why it makes no sense at all. An image that is sharp and
>> contains a lot of fine detail will be over-compressed and could potentially
>> be ruined by forcing a file size on it.

> I understand your point but I don't understand the mathematics. Apparently
> this Irfanview feature uses something called a "RIOT Plugin".

> Googling, I find RIOT stands for the "Radical Image Optimization Tool".
> http://criosweb.ro/software/RIOT.dll

> It looks like GIMP also utilizes the RIOT (http://luci.criosweb.ro/riot)
> Radical Image Optimiation Tool (http://registry.gimp.org/node/20778).

> I wish there were a Wikeipedia on this RIOT Radical Image Optimization
> Tool; but none yet.

> So, I guess, the real question, is how well does the RIOT Radical Image
> Optimization Tool work in Irfanview batch mode. (works well enough for me)

There are plenty of features that work well that generally speaking
are silly things to do.

--
Chris Malcolm
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