Dots per inch question

I once knew the answer to this, but I forgot. I use a Nikon CoolPix, but I
also have slides scanned to Kodak's photo CD. The show up in my image
editing app as 72dpi, and we just got a printer that claims to print up to
4800 x 2400 dpi. I can set the resolution in my image editing program, so
I've just re-set the 72x72 as 300x300 and printed a scanned Photo CD image
at 13 inches x 19 inches, and it's a stunner. (Uh, good stun, not bad
stun.)

The files in the Photo CD are .pcd, so I assume there's 4800 x 2400 dpi in
there somewhere, right? I can set my image editor to open at that
resolution and get it? My wife has a digital Rebel, and we'd like to get
maximum results from that camera, as well.

But what about the Nikon CoolPix images? Do I need one of those fractal
interpolators or whatever they're called?

(I realize whether anyone can tell the difference between 300 x300 and 4800
x 2400 is a different issue. I'm just trying to get a handle on how to
handle dots per inch. As a film shooter, this is not an issue I'm familiar
with.)
--
Philip Stripling | email to the replyto address is presumed
Legal Assistance on the Web | spam and read later. email to philip@
http://www.PhilipStripling.com/ | my domain is read daily.

"Phil Stripling" wrote in message
...

(snip)

(I realize whether anyone can tell the difference between 300 x300 and
4800
x 2400 is a different issue. I'm just trying to get a handle on how to
handle dots per inch. As a film shooter, this is not an issue I'm familiar
with.)
Philip Stripling

----------------

Phil,

You are making the same assumption and the same mistake here as many have
before you... so don't feel that you are alone in struggling with the
concepts. Pixels per inch (e.g. 72x72 or 300x300) are NOT the same thing as
dots per inch at the printer (4800x2400.) In printing the number of dots
required to make up one image pixel may range from none (for the colour
white - or really that is representing parts of the printed document with an
absence of any ink being laid down by the printer) to the other extreme of
several dots of each of the available inks to represent a single pixel.

When you ONLY make the change in resolution (72ppi to 300ppi) in the editor
all you actually do is reduce the "apparent" native size of a 100% scaled
image at the print stage.

Thus an image of 1600x1800 @72ppi image will tell you (in the image
properties in the editor) that it is ca 22x25 (printed) inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there is no re-sampling
done to get there. It is merely a scaling value for printing purposes.
Further, you can also set your printer to print that image at various
resolutions in dots per inch - whereupon the PRINTER DRIVER makes changes by
interpolation to the image file between receiving it in the print queue and
transmitting the data to the actual print heads - this is something you have
only very limited control over and only by changing print quality parameters
in the printer dialog between, say, draft quality and photo quality outputs
and altering (usually) the selected paper type to accommodate the print
quality (e.g. plain paper or photo paper). The printer, in turn, computes
the way that each pixel is managed as far as the inks, and quantity of inks,
laid down on the actual paper output.

So far I have not talked about making changes, except for the printer
quality settings, that affect image quality at the print stage... to do that
would involve a re-sampling step such as in the image editor. Taking the
original 72ppi image, for example, and command it to be 300ppi (ONLY reduces
"apparent" print output size) BUT also command a change in image size -
THEN - you will have made a change that is qualitative vs. the original
image file and that change will have required resampling (probably, and
almost certainly, creating data that was not part of the image in the first
place) in the editor stage and before the printer gets it.

Using the same image I used above: 1600x1800 image @300ppi the image
properties will tell you that it is 5.3x6 (printed) inches when scaled at
100% - I could command this to remain at 300ppi resolution but change the
print size to, say, 10x12 (a multiplier of 4x total pixels and a dimension
multiplier in each direction of 2x) and that image will then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are created out of some
(usually selectable) resampling algorithm - but they are nevertheless
machine created and incorporated into the original image. The native print
size, scaled at 100% in the printer, is then as selected, 10x12inches
@300pixels per inch.

Journalist

"Phil Stripling" wrote in message
...

(snip)

(I realize whether anyone can tell the difference between 300 x300 and
4800
x 2400 is a different issue. I'm just trying to get a handle on how to
handle dots per inch. As a film shooter, this is not an issue I'm familiar
with.)
Philip Stripling

----------------

Phil,

You are making the same assumption and the same mistake here as many have
before you... so don't feel that you are alone in struggling with the
concepts. Pixels per inch (e.g. 72x72 or 300x300) are NOT the same thing as
dots per inch at the printer (4800x2400.) In printing the number of dots
required to make up one image pixel may range from none (for the colour
white - or really that is representing parts of the printed document with an
absence of any ink being laid down by the printer) to the other extreme of
several dots of each of the available inks to represent a single pixel.

When you ONLY make the change in resolution (72ppi to 300ppi) in the editor
all you actually do is reduce the "apparent" native size of a 100% scaled
image at the print stage.

Thus an image of 1600x1800 @72ppi image will tell you (in the image
properties in the editor) that it is ca 22x25 (printed) inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there is no re-sampling
done to get there. It is merely a scaling value for printing purposes.
Further, you can also set your printer to print that image at various
resolutions in dots per inch - whereupon the PRINTER DRIVER makes changes by
interpolation to the image file between receiving it in the print queue and
transmitting the data to the actual print heads - this is something you have
only very limited control over and only by changing print quality parameters
in the printer dialog between, say, draft quality and photo quality outputs
and altering (usually) the selected paper type to accommodate the print
quality (e.g. plain paper or photo paper). The printer, in turn, computes
the way that each pixel is managed as far as the inks, and quantity of inks,
laid down on the actual paper output.

So far I have not talked about making changes, except for the printer
quality settings, that affect image quality at the print stage... to do that
would involve a re-sampling step such as in the image editor. Taking the
original 72ppi image, for example, and command it to be 300ppi (ONLY reduces
"apparent" print output size) BUT also command a change in image size -
THEN - you will have made a change that is qualitative vs. the original
image file and that change will have required resampling (probably, and
almost certainly, creating data that was not part of the image in the first
place) in the editor stage and before the printer gets it.

Using the same image I used above: 1600x1800 image @300ppi the image
properties will tell you that it is 5.3x6 (printed) inches when scaled at
100% - I could command this to remain at 300ppi resolution but change the
print size to, say, 10x12 (a multiplier of 4x total pixels and a dimension
multiplier in each direction of 2x) and that image will then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are created out of some
(usually selectable) resampling algorithm - but they are nevertheless
machine created and incorporated into the original image. The native print
size, scaled at 100% in the printer, is then as selected, 10x12inches
@300pixels per inch.

Journalist

"Phil Stripling" wrote in message
...

(snip)

(I realize whether anyone can tell the difference between 300 x300 and
4800
x 2400 is a different issue. I'm just trying to get a handle on how to
handle dots per inch. As a film shooter, this is not an issue I'm familiar
with.)
Philip Stripling

----------------

Phil,

You are making the same assumption and the same mistake here as many have
before you... so don't feel that you are alone in struggling with the
concepts. Pixels per inch (e.g. 72x72 or 300x300) are NOT the same thing as
dots per inch at the printer (4800x2400.) In printing the number of dots
required to make up one image pixel may range from none (for the colour
white - or really that is representing parts of the printed document with an
absence of any ink being laid down by the printer) to the other extreme of
several dots of each of the available inks to represent a single pixel.

When you ONLY make the change in resolution (72ppi to 300ppi) in the editor
all you actually do is reduce the "apparent" native size of a 100% scaled
image at the print stage.

Thus an image of 1600x1800 @72ppi image will tell you (in the image
properties in the editor) that it is ca 22x25 (printed) inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there is no re-sampling
done to get there. It is merely a scaling value for printing purposes.
Further, you can also set your printer to print that image at various
resolutions in dots per inch - whereupon the PRINTER DRIVER makes changes by
interpolation to the image file between receiving it in the print queue and
transmitting the data to the actual print heads - this is something you have
only very limited control over and only by changing print quality parameters
in the printer dialog between, say, draft quality and photo quality outputs
and altering (usually) the selected paper type to accommodate the print
quality (e.g. plain paper or photo paper). The printer, in turn, computes
the way that each pixel is managed as far as the inks, and quantity of inks,
laid down on the actual paper output.

So far I have not talked about making changes, except for the printer
quality settings, that affect image quality at the print stage... to do that
would involve a re-sampling step such as in the image editor. Taking the
original 72ppi image, for example, and command it to be 300ppi (ONLY reduces
"apparent" print output size) BUT also command a change in image size -
THEN - you will have made a change that is qualitative vs. the original
image file and that change will have required resampling (probably, and
almost certainly, creating data that was not part of the image in the first
place) in the editor stage and before the printer gets it.

Using the same image I used above: 1600x1800 image @300ppi the image
properties will tell you that it is 5.3x6 (printed) inches when scaled at
100% - I could command this to remain at 300ppi resolution but change the
print size to, say, 10x12 (a multiplier of 4x total pixels and a dimension
multiplier in each direction of 2x) and that image will then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are created out of some
(usually selectable) resampling algorithm - but they are nevertheless
machine created and incorporated into the original image. The native print
size, scaled at 100% in the printer, is then as selected, 10x12inches
@300pixels per inch.

Journalist

"Journalist-North" writes:

SNIP
Thus an image of 1600x1800 @72ppi image will tell you (in the image
properties in the editor) that it is ca 22x25 (printed) inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there is no re-sampling
done to get there. It is merely a scaling value for printing purposes.
Further, you can also set your printer to print that image at various
resolutions in dots per inch - whereupon the PRINTER DRIVER makes changes by
interpolation to the image file between receiving it in the print queue and
transmitting the data to the actual print heads - this is something you have
only very limited control over and only by changing print quality parameters
in the printer dialog between, say, draft quality and photo quality outputs
and altering (usually) the selected paper type to accommodate the print
quality (e.g. plain paper or photo paper). The printer, in turn, computes
the way that each pixel is managed as far as the inks, and quantity of inks,
laid down on the actual paper output.

Okay, so now I remember why I can't remember the answer.


So far I have not talked about making changes, except for the printer
SNIP

Yeah, that's why I can't remember, alright.

Using the same image I used above: 1600x1800 image @300ppi the image
properties will tell you that it is 5.3x6 (printed) inches when scaled at
100% - I could command this to remain at 300ppi resolution but change the
print size to, say, 10x12 (a multiplier of 4x total pixels and a dimension
multiplier in each direction of 2x) and that image will then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are created out of some
(usually selectable) resampling algorithm - but they are nevertheless
machine created and incorporated into the original image. The native print
size, scaled at 100% in the printer, is then as selected, 10x12inches
@300pixels per inch.

Uh, thanks for the reminder. :-

--
Philip Stripling | email to the replyto address is presumed
Legal Assistance on the Web | spam and read later. email to philip@
http://www.PhilipStripling.com/ | my domain is read daily.

"Journalist-North" writes:

SNIP
Thus an image of 1600x1800 @72ppi image will tell you (in the image
properties in the editor) that it is ca 22x25 (printed) inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there is no re-sampling
done to get there. It is merely a scaling value for printing purposes.
Further, you can also set your printer to print that image at various
resolutions in dots per inch - whereupon the PRINTER DRIVER makes changes by
interpolation to the image file between receiving it in the print queue and
transmitting the data to the actual print heads - this is something you have
only very limited control over and only by changing print quality parameters
in the printer dialog between, say, draft quality and photo quality outputs
and altering (usually) the selected paper type to accommodate the print
quality (e.g. plain paper or photo paper). The printer, in turn, computes
the way that each pixel is managed as far as the inks, and quantity of inks,
laid down on the actual paper output.

Okay, so now I remember why I can't remember the answer.


So far I have not talked about making changes, except for the printer
SNIP

Yeah, that's why I can't remember, alright.

Using the same image I used above: 1600x1800 image @300ppi the image
properties will tell you that it is 5.3x6 (printed) inches when scaled at
100% - I could command this to remain at 300ppi resolution but change the
print size to, say, 10x12 (a multiplier of 4x total pixels and a dimension
multiplier in each direction of 2x) and that image will then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are created out of some
(usually selectable) resampling algorithm - but they are nevertheless
machine created and incorporated into the original image. The native print
size, scaled at 100% in the printer, is then as selected, 10x12inches
@300pixels per inch.

Uh, thanks for the reminder. :-

--
Philip Stripling | email to the replyto address is presumed
Legal Assistance on the Web | spam and read later. email to philip@
http://www.PhilipStripling.com/ | my domain is read daily.

"Journalist-North" writes:

SNIP
Thus an image of 1600x1800 @72ppi image will tell you (in the image
properties in the editor) that it is ca 22x25 (printed) inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there is no re-sampling
done to get there. It is merely a scaling value for printing purposes.
Further, you can also set your printer to print that image at various
resolutions in dots per inch - whereupon the PRINTER DRIVER makes changes by
interpolation to the image file between receiving it in the print queue and
transmitting the data to the actual print heads - this is something you have
only very limited control over and only by changing print quality parameters
in the printer dialog between, say, draft quality and photo quality outputs
and altering (usually) the selected paper type to accommodate the print
quality (e.g. plain paper or photo paper). The printer, in turn, computes
the way that each pixel is managed as far as the inks, and quantity of inks,
laid down on the actual paper output.

Okay, so now I remember why I can't remember the answer.


So far I have not talked about making changes, except for the printer
SNIP

Yeah, that's why I can't remember, alright.

Using the same image I used above: 1600x1800 image @300ppi the image
properties will tell you that it is 5.3x6 (printed) inches when scaled at
100% - I could command this to remain at 300ppi resolution but change the
print size to, say, 10x12 (a multiplier of 4x total pixels and a dimension
multiplier in each direction of 2x) and that image will then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are created out of some
(usually selectable) resampling algorithm - but they are nevertheless
machine created and incorporated into the original image. The native print
size, scaled at 100% in the printer, is then as selected, 10x12inches
@300pixels per inch.

Uh, thanks for the reminder. :-

--
Philip Stripling | email to the replyto address is presumed
Legal Assistance on the Web | spam and read later. email to philip@
http://www.PhilipStripling.com/ | my domain is read daily.

You are making the same assumption and the same mistake
here as many have
before you... so don't feel that you are alone in
struggling with the
concepts. Pixels per inch (e.g. 72x72 or 300x300) are NOT
the same thing as
dots per inch at the printer (4800x2400.) In printing the
number of dots
required to make up one image pixel may range from none
(for the colour
white - or really that is representing parts of the
printed document with an
absence of any ink being laid down by the printer) to the
other extreme of
several dots of each of the available inks to represent a
single pixel.

When you ONLY make the change in resolution (72ppi to
300ppi) in the editor
all you actually do is reduce the "apparent" native size
of a 100% scaled
image at the print stage.

Thus an image of 1600x1800 @72ppi image will tell you (in
the image
properties in the editor) that it is ca 22x25 (printed)
inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will
tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there
is no re-sampling
done to get there. It is merely a scaling value for
printing purposes.
Further, you can also set your printer to print that image
at various
resolutions in dots per inch - whereupon the PRINTER
DRIVER makes changes by
interpolation to the image file between receiving it in
the print queue and
transmitting the data to the actual print heads - this is
something you have
only very limited control over and only by changing print
quality parameters
in the printer dialog between, say, draft quality and
photo quality outputs
and altering (usually) the selected paper type to
accommodate the print
quality (e.g. plain paper or photo paper). The printer, in
turn, computes
the way that each pixel is managed as far as the inks, and
quantity of inks,
laid down on the actual paper output.

So far I have not talked about making changes, except for
the printer
quality settings, that affect image quality at the print
stage... to do that
would involve a re-sampling step such as in the image
editor. Taking the
original 72ppi image, for example, and command it to be
300ppi (ONLY reduces
"apparent" print output size) BUT also command a change in
image size -
THEN - you will have made a change that is qualitative vs.
the original
image file and that change will have required resampling
(probably, and
almost certainly, creating data that was not part of the
image in the first
place) in the editor stage and before the printer gets it.

Using the same image I used above: 1600x1800 image @300ppi
the image
properties will tell you that it is 5.3x6 (printed) inches
when scaled at
100% - I could command this to remain at 300ppi resolution
but change the
print size to, say, 10x12 (a multiplier of 4x total pixels
and a dimension
multiplier in each direction of 2x) and that image will
then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are
created out of some
(usually selectable) resampling algorithm - but they are
nevertheless
machine created and incorporated into the original image.
The native print
size, scaled at 100% in the printer, is then as selected,
10x12inches
@300pixels per inch.

Journalist

That is a very excellent explanation of the issue, however I
don't understand it in a practical way. To use your
example, is it best to resample an image to 3200x3600 @
300ppi if you wish to make a 10x12 print, or do the photo
apps handle this in the background before they send the data
to the printer?

Swingman wrote:
You are making the same assumption and the same mistake
here as many have
before you... so don't feel that you are alone in
struggling with the
concepts. Pixels per inch (e.g. 72x72 or 300x300) are NOT
the same thing as
dots per inch at the printer (4800x2400.) In printing the
number of dots
required to make up one image pixel may range from none
(for the colour
white - or really that is representing parts of the
printed document with an
absence of any ink being laid down by the printer) to the
other extreme of
several dots of each of the available inks to represent a
single pixel.

When you ONLY make the change in resolution (72ppi to
300ppi) in the editor
all you actually do is reduce the "apparent" native size
of a 100% scaled
image at the print stage.

Thus an image of 1600x1800 @72ppi image will tell you (in
the image
properties in the editor) that it is ca 22x25 (printed)
inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will
tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there
is no re-sampling
done to get there. It is merely a scaling value for
printing purposes.
Further, you can also set your printer to print that image
at various
resolutions in dots per inch - whereupon the PRINTER
DRIVER makes changes by
interpolation to the image file between receiving it in
the print queue and
transmitting the data to the actual print heads - this is
something you have
only very limited control over and only by changing print
quality parameters
in the printer dialog between, say, draft quality and
photo quality outputs
and altering (usually) the selected paper type to
accommodate the print
quality (e.g. plain paper or photo paper). The printer, in
turn, computes
the way that each pixel is managed as far as the inks, and
quantity of inks,
laid down on the actual paper output.

So far I have not talked about making changes, except for
the printer
quality settings, that affect image quality at the print
stage... to do that
would involve a re-sampling step such as in the image
editor. Taking the
original 72ppi image, for example, and command it to be
300ppi (ONLY reduces
"apparent" print output size) BUT also command a change in
image size -
THEN - you will have made a change that is qualitative vs.
the original
image file and that change will have required resampling
(probably, and
almost certainly, creating data that was not part of the
image in the first
place) in the editor stage and before the printer gets it.

Using the same image I used above: 1600x1800 image @300ppi
the image
properties will tell you that it is 5.3x6 (printed) inches
when scaled at
100% - I could command this to remain at 300ppi resolution
but change the
print size to, say, 10x12 (a multiplier of 4x total pixels
and a dimension
multiplier in each direction of 2x) and that image will
then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are
created out of some
(usually selectable) resampling algorithm - but they are
nevertheless
machine created and incorporated into the original image.
The native print
size, scaled at 100% in the printer, is then as selected,
10x12inches
@300pixels per inch.

Journalist


That is a very excellent explanation of the issue, however I
don't understand it in a practical way. To use your
example, is it best to resample an image to 3200x3600 @
300ppi if you wish to make a 10x12 print, or do the photo
apps handle this in the background before they send the data
to the printer?



If your Photo Editor has Bicubic Sampling (like Photoshop), I'd let your
Photo Editor do the resampling. You can never be sure how the printer
driver upsamples the image you send it.
Bob Williams

Swingman wrote:
You are making the same assumption and the same mistake
here as many have
before you... so don't feel that you are alone in
struggling with the
concepts. Pixels per inch (e.g. 72x72 or 300x300) are NOT
the same thing as
dots per inch at the printer (4800x2400.) In printing the
number of dots
required to make up one image pixel may range from none
(for the colour
white - or really that is representing parts of the
printed document with an
absence of any ink being laid down by the printer) to the
other extreme of
several dots of each of the available inks to represent a
single pixel.

When you ONLY make the change in resolution (72ppi to
300ppi) in the editor
all you actually do is reduce the "apparent" native size
of a 100% scaled
image at the print stage.

Thus an image of 1600x1800 @72ppi image will tell you (in
the image
properties in the editor) that it is ca 22x25 (printed)
inches when scaled
at 100%, BUT, the exact same 1600x1800 image @300ppi will
tell you that it
is 5.3x6 (printed) inches when scaled at 100% - AND there
is no re-sampling
done to get there. It is merely a scaling value for
printing purposes.
Further, you can also set your printer to print that image
at various
resolutions in dots per inch - whereupon the PRINTER
DRIVER makes changes by
interpolation to the image file between receiving it in
the print queue and
transmitting the data to the actual print heads - this is
something you have
only very limited control over and only by changing print
quality parameters
in the printer dialog between, say, draft quality and
photo quality outputs
and altering (usually) the selected paper type to
accommodate the print
quality (e.g. plain paper or photo paper). The printer, in
turn, computes
the way that each pixel is managed as far as the inks, and
quantity of inks,
laid down on the actual paper output.

So far I have not talked about making changes, except for
the printer
quality settings, that affect image quality at the print
stage... to do that
would involve a re-sampling step such as in the image
editor. Taking the
original 72ppi image, for example, and command it to be
300ppi (ONLY reduces
"apparent" print output size) BUT also command a change in
image size -
THEN - you will have made a change that is qualitative vs.
the original
image file and that change will have required resampling
(probably, and
almost certainly, creating data that was not part of the
image in the first
place) in the editor stage and before the printer gets it.

Using the same image I used above: 1600x1800 image @300ppi
the image
properties will tell you that it is 5.3x6 (printed) inches
when scaled at
100% - I could command this to remain at 300ppi resolution
but change the
print size to, say, 10x12 (a multiplier of 4x total pixels
and a dimension
multiplier in each direction of 2x) and that image will
then have apparent
values of ca 3200x3600 @300ppi - the extra pixels are
created out of some
(usually selectable) resampling algorithm - but they are
nevertheless
machine created and incorporated into the original image.
The native print
size, scaled at 100% in the printer, is then as selected,
10x12inches
@300pixels per inch.

Journalist


That is a very excellent explanation of the issue, however I
don't understand it in a practical way. To use your
example, is it best to resample an image to 3200x3600 @
300ppi if you wish to make a 10x12 print, or do the photo
apps handle this in the background before they send the data
to the printer?



If your Photo Editor has Bicubic Sampling (like Photoshop), I'd let your
Photo Editor do the resampling. You can never be sure how the printer
driver upsamples the image you send it.
Bob Williams