I cannot answer your question directly but I understand that to protect
yourself you are loading a picture at 21 dpi. I don't know how you achieved
21 dpi, maybe the software you use does this for you. Here is my take on
your question.
The correct resolution is not dpi, this is for printing. The correct
resolution is the dimension in pixels. So the software you use must be using
the pixel dimensions of your picture and downsizing it so nobody can print a
decent size print since 21 dpi would produce a lousy print and so would 25.
I do not use the software you name except for Irfanview.
Here is an example using Irfanview.
I open an image in Irfanview and click on Image and Information. This is
what I get:
Resolution: 72 x 72 dpi and next to this is a Set button
Original size: 2560 x 1920 pixels
Print size from DPI: 35.56 x 26.67
What does this mean. It means that if I decide to print using 72 x 72 dpi, I
can print as big as 35.56 x 26.67 (simply dividing 2560 by 72 and 1920 by
72). The print will be large but the quality will be terrible because the
print resolution (72 x 72 dpi) is too low. This resolution is fine on the
computer screen but lousy for a print. So, now I decide to get a better
print and I change the resolution from the number shown in Irfanview (72 x
72) to 320 x 320 and I click on the Set button. Now look at the print size.
It has changed to 8.00 x 6.00 in. At this printing resolution (provided I
have a printer that can do this) I will get a top notch print. But 8 x 6 may
be a little too small, I want a larger print. If so, I decrease from 320 but
you really can't decrease much below 220 because the quality of the print
will deteriorate. So, with the example above it would be 2560/220 x
1920/220= 11.6 x 8.7 in print.
So, when you post on the web you post "low resolution" images in pixels, not
in dpi.
If you post an image 220 x 220 pixels, I can print a very good 1 x 1 in.
print of your picture. Anything above this will have poor quality. However,
if I really want to, software is available to get a fairly good print at
about 6 x 4 of your 220 x 220 pixels picture.
Since I do not use the software you have (except Irfanview), my best guess
is that the dpi resolution shown by three (22 dpi) correspond to the same
maximum size they will print at and they are opening the image at a
particular screen resolution, while the one showing 25 dpi will have a
slightly lower maximum size it will print at and is opening at a different
screen resolution. A best guess, not an absolute answer.
Gulper said:
I have an jpg.image on the internet which for copyright reasons may not be displayed at higher
than 21 dpi.
I used Paint shop Pro 8, Photo Impact SE and Irfanview to verify the
resolutions before I uploaded my jpg to the web.
I now find that Microsoft Photo Editor contradicts these 3 applications
and shows the resolutions to be 25 dpi.
