DPI and PPI

Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?

However according to Microsoft Office Picture Manager the images that I
receive from different cameras have very different DPIs - ranging
from 72 to 300. Since I need to print these images they have to be at
least 300DPI. So my question is - is there a way that one can change
the PPI/DPI your camera takes photos with. I've notices that when I
change the resolution setting on my camera, my photos still come in at
180 DPI.

Thanks

Dalene

"Dalene" wrote in message
oups.com...
Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?

However according to Microsoft Office Picture Manager the images that I
receive from different cameras have very different DPIs - ranging
from 72 to 300. Since I need to print these images they have to be at
least 300DPI. So my question is - is there a way that one can change
the PPI/DPI your camera takes photos with. I've notices that when I
change the resolution setting on my camera, my photos still come in at
180 DPI.

Thanks

Dalene


Cameras have resolution, i.e. 2544 x 1696 not ppi (pixels per inch). dpi,
dots per inch, is a printer term; it refers to the density of the ink dots
that are used to create the image on paper. You've no doubt noted specs on
printers - 1440dpi, 2880dpi, etc.. The two terms aren't related. Send an
image to your printer at 72ppi, and even if the printer is at 5760dpi, it'll
still look terrible - it'll just use more ink. Anyway, none of the cameras
I've had have a ppi setting. Just set the ppi at 300 for the image size at
the time of printing.

Mark

On 12 Jul 2006 02:51:57 -0700, "Dalene" wrote:

Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?


wrong .. no camera takes pictures at any PPI .. cameras take pictures
at an X-by-Y pixel matrix and that's it .. the PPI indications is
there for god knows what reason !
It is only relevant in a printing environment .. check the Inet for
more details, this has been debated ad vitam aeternam ! :-) (or should
I say "ad nauseam" ? :-))

imbsysop wrote:
On 12 Jul 2006 02:51:57 -0700, "Dalene" wrote:


Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?



wrong .. no camera takes pictures at any PPI .. cameras take pictures
at an X-by-Y pixel matrix and that's it .. the PPI indications is
there for god knows what reason !

Wrong in your turn.

Since the sensor has a size (expressible in inches)
and a pixel count, it clearly has a resolution
in pixels per inch.

This figure is (however) of limited
practical use.

BugBear

imbsysop wrote:
On 12 Jul 2006 02:51:57 -0700, "Dalene" wrote:

Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?


wrong .. no camera takes pictures at any PPI .. cameras take pictures
at an X-by-Y pixel matrix and that's it .. the PPI indications is
there for god knows what reason !
It is only relevant in a printing environment .. check the Inet for
more details, this has been debated ad vitam aeternam ! :-) (or should
I say "ad nauseam" ? :-))

Thats right ppi is just a guide to display the camera XY pixel count at
a certain size, in many ways arbitrary number. dpi is a term used in
printing which has wrongly been used to describe ppi for years.
Probably going back to the the start of the use of digital cameras when
photographers had to talk to crusty pressmen. Probably everyone who has
been in this end of the business is guilty of slipping once in a while.
So if you are talking digital photography and someone says dpi, they
really mean ppi. If you are talking printing dpi and ppi are different
things. The other term that gets thrown in here is lpi (lines per inch)
which is a screen printing term.
For digital photography ppi controls the final size of a XY dimensions
of a digital sensor. One reaso I like the D200 is a 10mp sensor @
300ppi gives an 8x12 inch print.

Tom

On Wed, 12 Jul 2006 13:04:10 +0100, bugbear
wrote:

imbsysop wrote:
On 12 Jul 2006 02:51:57 -0700, "Dalene" wrote:


Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?



wrong .. no camera takes pictures at any PPI .. cameras take pictures
at an X-by-Y pixel matrix and that's it .. the PPI indications is
there for god knows what reason !

Wrong in your turn.

Since the sensor has a size (expressible in inches)
and a pixel count, it clearly has a resolution
in pixels per inch.

This figure is (however) of limited
practical use.

ROTFLMAO .. kindly express the resolution in PPI of a 7Mpx and 1/2.5"
sensor .. ?

For the X axis and this sensor this must be something around 13546 PPI
! LMAO, speaking of a "limited use" ! I like the logic of some of my
fellow planet inhabitants ! braindead humbug !

Cameras have resolution, i.e. 2544 x 1696 not ppi (pixels per inch).
dpi,
dots per inch, is a printer term; it refers to the density of the ink
dots
that are used to create the image on paper. You've no doubt noted specs
on
printers - 1440dpi, 2880dpi, etc.. The two terms aren't related. Send
an
image to your printer at 72ppi, and even if the printer is at 5760dpi,
it'll
still look terrible - it'll just use more ink. Anyway, none of the
cameras
I've had have a ppi setting. Just set the ppi at 300 for the image size
at
the time of printing.

Mark

Most camera's use the exif field for ppi. A lot off camera's set this to 72
ppi.
But ppi or dpi is only a format which applies to when converting from and
to a picture. The in camera ppi is very high on the sensor and not used.
72 ppi (up to 100 ppi) is about the maximum a display can show.
Quality above 300 ppi is better than most people can see. So for printing
300 ppi is used. (Yes this is three times as high as your display).

The 72 ppi is about what you get if you display your picture on a 100 %
enlargement on your display.

The embedded information (72 ppi for example) is not used a lot. Sometimes
for printing, but then you probably want to alter that anyway, because you
want the picture to be of a difference size. So the embedded information
is not important.

ben

"Dalene" wrote in message
oups.com...
Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?

However according to Microsoft Office Picture Manager the images that I
receive from different cameras have very different DPIs - ranging
from 72 to 300. Since I need to print these images they have to be at
least 300DPI. So my question is - is there a way that one can change
the PPI/DPI your camera takes photos with. I've notices that when I
change the resolution setting on my camera, my photos still come in at
180 DPI.

Thanks

Dalene


Hi.

Cameras do not apply Ppi settings to images. These will be applied by a
Viewing or Editing program.

The Ppi figures do not actually change the image, they only describe how
closely packed the Pixels are.

If you have an image which is, for example, 2272 pxl x 1704 pxl, and it is
at 300Ppi, your picture will be roughly 7.5 inches x 5.6 inches, when sent
for printing.
If it is at 200Ppi your picture will be 11.3 x 8.5 inches in size, when sent
for printing.

In both cases the picture will still be 2272 x 1704 pixels, and the Ppi
figure has no other effect, or value, except for printing.

My version of Microsoft Office Picture Manager (Office 2003) does not
specify, anywhere I can find, the Ppi for any Jpeg or Tiff open in it. It
also does not seem to have any way of changing that.

It can Resize the picture, but that operation will add or remove Pixels
(Resampling or Interpolation), and that will have quality consequences.
It can also vary the amount of compression being applied when the image is
saved, and that can also have quality consequences.

Most Digital Image Editing Programs will have the ability to specify at
which Ppi an image will be imported into it, or at what Ppi it will be sent
for printing. Microsoft Office Picture Manager should not really be called
an Editing Program. It is far too limited to be of any real value.

There are a number of very much more capable programs available, some for
Free download. For example try Irfanview or Picassa.
Even the one which came with your Camera, although not great either, will be
of more use than the Microsoft Office one.

Changing the resolution on your Camera will probably change the actual
number of Pixels in the image, and not the Ppi.

For a very good explanation of Resolution and that sort of thing, have a
look at www.scantips.com

Roy G

imbsysop writes:

This figure is (however) of limited
practical use.

ROTFLMAO .. kindly express the resolution in PPI of a 7Mpx and 1/2.5"
sensor .. ?

For the X axis and this sensor this must be something around 13546 PPI
! LMAO, speaking of a "limited use" ! I like the logic of some of my
fellow planet inhabitants ! braindead humbug !

The actual PPI of the sensor is very useful if you want to do any
calculations involving actual image distances. For example, if you
have mounted the camera on a telescope, and see two features a certain
number of pixels apart in the image, you can determine their true
angular separation in the sky if you know the sensor PPI and the
telescope objective FL. Or if the camera is mounted on a microscope
and you know the microscope objective magnification, you can measure
distances in the subject.

Dave

"Dalene" writes:
Hi There

I have a somewhat technical question about PPI and DPI. I'll do my
best to ask my question as clearly as possible. I understand that all
digital cameras take images at 72 PPI which is similar to 72 DPI?

No. The actual PPI of the camera sensor is in the thousands of pixels
per inch. That's even stored in the EXIF data in some cases if you're
curious.

However, the PPI value you are talking about is an image header field
that specifies the PPI that should be used for *printing* the image, not
how it was captured. Some cameras might set this value in the image
they write, other cameras will leave the field empty.

However according to Microsoft Office Picture Manager the images that I
receive from different cameras have very different DPIs - ranging
from 72 to 300.

The images from cameras that do not set the PPI value will have some
default value assigned when you open them; that's probably where the
ones that appear to be 72 PPI come from. The other values are likely
set by the camera. But in all cases you can change the PPI with a
suitable image editor.

Since I need to print these images they have to be at
least 300DPI. So my question is - is there a way that one can change
the PPI/DPI your camera takes photos with. I've notices that when I
change the resolution setting on my camera, my photos still come in at
180 DPI.

Changing the resolution on your camera changes the *pixel count*, not
the PPI. You need an image editor that allows you to change the PPI. I
can't tell you how to do it in MS Office Picture Manager since I've
never used it (but I've generally found Microsoft products to have
exceptionally awful handling of images).

Dave