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From: John McWilliams on 18 Apr 2010 20:17
nospam wrote:
> In article <hqf86q$m7l$3(a)news.eternal-september.org>, Phillip Jones
> <pjones1(a)kimbanet.com> wrote:
>
>> You can open I photo and choose to save for email which down samples to
>> photos from 300-600 dpi or more to 72 DPI which reduces file sizes to
>> manageable size for emailing
>
> dpi is only relevant for printing. downsampling only changes the pixel
> count.

Yes, there's a major difference between PPI and DPI, the latter being a
printer or scanner setting.

--
john mcwilliams
From: Phillip Jones on 18 Apr 2010 21:42
nospam wrote:
> In article<hqf86q$m7l$3(a)news.eternal-september.org>, Phillip Jones
> <pjones1(a)kimbanet.com> wrote:
>
>> You can open I photo and choose to save for email which down samples to
>> photos from 300-600 dpi or more to 72 DPI which reduces file sizes to
>> manageable size for emailing
>
> dpi is only relevant for printing. downsampling only changes the pixel
> count.
But the downsampling reduces the file size because it throws away
discarded information.

--
Phillip M. Jones, C.E.T. "If it's Fixed, Don't Break it"
http://www.phillipmjones.net http://www.vpea.org
mailto:pjones1(a)kimbanet.com
From: Phillip Jones on 18 Apr 2010 21:46
John McWilliams wrote:
> nospam wrote:
>> In article<hqf86q$m7l$3(a)news.eternal-september.org>, Phillip Jones
>> <pjones1(a)kimbanet.com> wrote:
>>
>>> You can open I photo and choose to save for email which down samples to
>>> photos from 300-600 dpi or more to 72 DPI which reduces file sizes to
>>> manageable size for emailing
>>
>> dpi is only relevant for printing. downsampling only changes the pixel
>> count.
>
> Yes, there's a major difference between PPI and DPI, the latter being a
> printer or scanner setting.
>
Open a Jpeg in Graphic converter and change sampling Rate from 300 DPI
to 72 DPI and save as a slightly different name then compare size of
file often it 2 to 2-1/2 times as small as the original.

--
Phillip M. Jones, C.E.T. "If it's Fixed, Don't Break it"
http://www.phillipmjones.net http://www.vpea.org
mailto:pjones1(a)kimbanet.com
From: nospam on 18 Apr 2010 21:51
In article <hqgce0$7ce$2(a)news.eternal-september.org>, Phillip Jones
<pjones1(a)kimbanet.com> wrote:

> >> You can open I photo and choose to save for email which down samples to
> >> photos from 300-600 dpi or more to 72 DPI which reduces file sizes to
> >> manageable size for emailing
> >
> > dpi is only relevant for printing. downsampling only changes the pixel
> > count.
>
> But the downsampling reduces the file size because it throws away
> discarded information.

yes it does. dpi is not relevant.
From: nospam on 18 Apr 2010 21:53
In article <hqgcla$999$1(a)news.eternal-september.org>, Phillip Jones
<pjones1(a)kimbanet.com> wrote:

> > Yes, there's a major difference between PPI and DPI, the latter being a
> > printer or scanner setting.
>
> Open a Jpeg in Graphic converter and change sampling Rate from 300 DPI
> to 72 DPI and save as a slightly different name then compare size of
> file often it 2 to 2-1/2 times as small as the original.

dpi is not a sampling rate and changing it doesn't change the number of
pixels, it changes the size of the image when it's printed.

to change the number of pixels, you need to upsize or downsize.
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