how come need so high dpi for printing photos?

What do you mean by dpi? The dpi value of an inkjet printer is something
totally different from a monitor's dpi. Every image pixel has to be
assembled from a number of droplets of ink, while you have three brightness
values (R,G,B) assigned to each monitor pixel. With 24 bit color on an
inkjet printer you need 16 times the dpi of the monitor (256 spaces for
droplets).

"Bucky" <uw_badgers.DeleteThis@email.com> schrieb im Newsbeitrag
news:1168900932.928480.305360@m58g2000cwm.googlegroups.com...
>A 15" monitor at 1024x768 resolution is about 85 pixels per inch.
> Viewing a photo on the monitor at that resolution looks great, right?
>
> So how come if you print out a photo with the same resolution, size,
> density (1024x768, 12"x9", 85 dpi), the print will look very poor? Even
> if you hold the print at the same viewing distance as the monitor.
>
 >> Stay informed about: how come need so high dpi for printing photos? 

"Bucky" <uw_badgers DeleteThis @email.com> wrote in message
news:1168900932.928480.305360@m58g2000cwm.googlegroups.com...
>A 15" monitor at 1024x768 resolution is about 85 pixels per inch.
> Viewing a photo on the monitor at that resolution looks great, right?
>
> So how come if you print out a photo with the same resolution, size,
> density (1024x768, 12"x9", 85 dpi), the print will look very poor? Even
> if you hold the print at the same viewing distance as the monitor.

There are several reasons I can think of - others may add to this. The
first is that, compared to a piece of paper, the monitor is brighter, and
has a much larger dynamic range, so the loss in resolution more than made up
for by the overall impact of the image Second, we are used to the
underlying texture of TV images, and tend to filter it out or even treat it
as if it were part of the image's native resolution. No so with paper
prints, where we take the glossy sharpness of even 4x6 prints for granted,
and are very sensitive to unwanted texture and jaggies. Third, we do tend
to hold even an 8x10 print very close to our eyes.

There are some practical ideas that follow from this. It should be possible
to make an acceptable print at the approximately 72 ppi resolution of a
monitor. To do so, make sure you use the full dynamic range of the image,
and use sharpening as much as possible. Photographers have long known that
softer images can be made to appear sharper by increasing the grain, and
printing on a textured paper. So add texture to the image, so that the eye
always has something to lock on to, even at close examination.
--
Mike Russell
www.curvemeister.com/forum/
 >> Stay informed about: how come need so high dpi for printing photos? 

"Bucky" <uw_badgers.TakeThisOut@email.com> wrote in message
news:1168900932.928480.305360@m58g2000cwm.googlegroups.com...
>A 15" monitor at 1024x768 resolution is about 85 pixels per inch.
> Viewing a photo on the monitor at that resolution looks great, right?
>
> So how come if you print out a photo with the same resolution, size,
> density (1024x768, 12"x9", 85 dpi), the print will look very poor? Even
> if you hold the print at the same viewing distance as the monitor.
>

Does "Why" really matter ???

You can print at 72 Ppi or 96 Ppi if you want, and if you think the results
are Ok, fine.

If the results are not good enough, then print at a higher Ppi, until you
get the quality you want.

Life is too short.

Roy G
 >> Stay informed about: how come need so high dpi for printing photos? 

In article <1168900932.928480.305360 RemoveThis @m58g2000cwm.googlegroups.com>,
"Bucky" <uw_badgers RemoveThis @email.com> wrote:

> A 15" monitor at 1024x768 resolution is about 85 pixels per inch.
> Viewing a photo on the monitor at that resolution looks great, right?
>
> So how come if you print out a photo with the same resolution, size,
> density (1024x768, 12"x9", 85 dpi), the print will look very poor? Even
> if you hold the print at the same viewing distance as the monitor.

In very basic terms, my understanding is:

Even with the best monitors and the best software you never see on
screen the full resolution of a file that is very resolute. The monitor
down samples the image a lot for viewing in the case of the file you
have its perhaps up sampling it a bit. Monitors are around 72-96 DPI.


--
Would thou choose to meet a rat eating dragon, or
a dragon, eating rat? The answer of: I am somewhere
in the middle. "Me who is part taoist and part Christian".
 >> Stay informed about: how come need so high dpi for printing photos? 

In article <eHVqh.537$8j7.368@newsfe1-win.ntli.net>,
"Roy G" <roy.gibson1 DeleteThis @REMOVE.tesco.net> wrote:

> If the results are not good enough, then print at a higher Ppi, until you
> get the quality you want.

Uh huh, from a native file resolution of 85 dpi. *Sure you will*. :-/

--
Would thou choose to meet a rat eating dragon, or
a dragon, eating rat? The answer of: I am somewhere
in the middle. "Me who is part taoist and part Christian".
 >> Stay informed about: how come need so high dpi for printing photos? 

Little Green Eyed Dragon wrote:
> Even with the best monitors and the best software you never see on
> screen the full resolution of a file that is very resolute. The monitor
> down samples the image a lot for viewing in the case of the file you
> have its perhaps up sampling it a bit. Monitors are around 72-96 DPI.

I probably should have been clearer in my question. Let's say I have an
image that is 1024x768 pixels. When I view it on a 15" monitor, it
looks great (no downsampling).

Now I print the same 1024x768 image on a 12"x9" print (that is the
exact physical size as the monitor). But it doesn't look nearly as good
as the monitor.
 >> Stay informed about: how come need so high dpi for printing photos? 

Cgiorgio wrote:

> What do you mean by dpi? The dpi value of an inkjet printer is
> something totally different from a monitor's dpi.

Bucky means PPI - Pixels Per Inch. When printing, these gets converted
to the printers higher resolution in order to reproduce the dots, as
you try to explain.

So Bucky has two images, each about 85 PPI, one of them also 85 DPI
(the one on the monitor), the other one 2400 DPI or whatever his
printer is capable of.

> Every image pixel has to be assembled from a number of droplets of
> ink, while you have three brightness values (R,G,B) assigned to each
> monitor pixel. With 24 bit color on an inkjet printer you need 16
> times the dpi of the monitor (256 spaces for droplets).

That only explains why inkjets have such high resolution, not why they
should need more pixels than a monitor.

Mike's explanation sounds right. I don't think the sharpening would
work, though, but it's easy to try out.
--
Toke Eskildsen - http://ekot.dk/
 >> Stay informed about: how come need so high dpi for printing photos? 

Toke Eskildsen wrote:

> So Bucky has two images, each about 85 PPI, one of them also 85
> DPI (the one on the monitor), the other one 2400 DPI or whatever
> his printer is capable of.

Correction: The one on the monitor is 255 DPI, as the monitor uses
three colors with variable intensity for reproduction.
--
Toke Eskildsen - http://ekot.dk/
 >> Stay informed about: how come need so high dpi for printing photos? 

Bucky wrote:
> Cgiorgio wrote:
>> Every image pixel has to be
>> assembled from a number of droplets of ink, while you have three brightness
>> values (R,G,B) assigned to each monitor pixel.
>
> I see now. Wikipedia says something similar too (should have looked
> there first!):
>
> "The DPI measurement of a printer often needs to be considerably higher
> than the pixels per inch (PPI) measurement of a video display in order
> to produce similar-quality output. This is due to the limited range of
> colours for each dot typically available on a printer. At each dot
> position, the simplest type of colour printer can only either print no
> dot, or a dot consisting of a fixed volume of ink in each of four
> colour channels (typically CMYK with cyan, magenta, yellow and black
> ink)."
> http://en.wikipedia.org/wiki/Dots_per_inch
>
> I didn't know that printers only had "1-bit depth" for each color
> channel. I mistakenly thought that printers could vary the volume of
> ink per dot, like a monitor. So if there was a printer that could vary
> the volume of ink per dot by 256 different levels, then the 85 dpi
> print would be comparable to the monitor, correct?
>

Some printers CAN vary the size of each ink dot (HP does it), but the
number of sizes available isn't large, thus you need a lot of smaller
dots to get the same effective resolution. EACH pixel on the screen can
have all the various colors, and intensities. The fact that the monitor
emits light, and the print reflects it, also pays a part in the
perception of clarity.
 >> Stay informed about: how come need so high dpi for printing photos? 

Keith Sheppard wrote:
>
> The printer therefore has to use several dots for each pixel. The more dots
> it uses for any one pixel the greater the colour repertoire but the lower
> the resolution of the printed image.
>
> I hope that explains it.
>

But does it? My printer resolves around 480ppi on glossy paper. If I
print at 85ppi (say), the result looks horrible. If I then photograph
the print with a macro lens, it is obvious that the dots are much
smaller than the pixels (I can clearly distinguish both the dots and
the pixels) [it's an Epson R800, which does have a small dot size; it's
completely invisible to the naked eyes, even my short-sighted ones]. In
other words, each printed pixel can have one of many colours. I am
pretty sure that the reason it looks worse than the screen is not what
you say (because I thought so as well when I just got the printer, but,
by looking at low-resolution printouts, concluded that it is not true).

I think what Mike Russel said is probably correct (at least, it is part
of the reason): we're used to looking at low-resolution screen images.
Find an image of a tree against the sky with lots of small details;
print it out a full resolution, and compare it to the downsized one on
the screen. The difference in detail visibility is night and day, and
yet I, at least, would not really have noticed it unless I was
specifically thinking about details.
 >> Stay informed about: how come need so high dpi for printing photos? 

Don't confuse dots per inch with pixels per inch.

Your monitor has three guns, one for each of red green and blue, but they're
not just on or off. Each dot on your computer screen can vary in intensity
from off, through dim, medium, bright to very bright. Typically there might
be 256 brightness levels for each individual dot.

So a monitor can use just three dots (one each of red, green and blue) to
make a pixel of any colour from a repertoire of millions.

A printer is a bit different. Printers don't actually mix colour inks in
the same way an artist would mix paint. Either there's ink (of just one
colour) at any given point on the page or there isn't. Many printers carry
only three colours of ink (some have more and I'm ignoring black for the
purposes of illustration). To achieve any given colour it is therefore
necessary for the printer to spray a pattern of dots of different colours to
give the eye the impression of the chosen colour.

The printer therefore has to use several dots for each pixel. The more dots
it uses for any one pixel the greater the colour repertoire but the lower
the resolution of the printed image.

I hope that explains it.

Keith
 >> Stay informed about: how come need so high dpi for printing photos? 

>>Does "Why" really matter ???

To some of us with enquiring minds, "why" always matters.
Keith
 >> Stay informed about: how come need so high dpi for printing photos? 

dennis@home wrote:
> "acl" <achilleaslazarides.TakeThisOut@yahoo.co.uk> wrote in message
> news:1168952302.469729.107090@a75g2000cwd.googlegroups.com...
>
> > But does it? My printer resolves around 480ppi on glossy paper. If I
> > print at 85ppi (say), the result looks horrible.
>
> Suppose you want 256 levels of red printed.
> You need to print 0-255 dots for that red pixel.
> That would be a square 16 x 16.
> A 480dpi printer cannot do that at 85ppi. It could at 30ppi.
>
> If your printer can do variable drop sizes it can do that 256 different
> levels in less dots.. say 64 or 8x8.
>
> This is a simplistic view as printers seldom actually use square pixels.

Well, the printer is supposed to be 5760dpi in the horizontal
direction, which I interpret to mean 2880x1440dpi in reality (with some
kind of intelligent dot placement, as I can clearly see it's not
5760dpi if I photograph it using a macro lens). I meant that it
actually resolves 480ppi (ie if I create 1 pixel wide lines spaced by 1
pixel and send them to be printed at 480dpi, it actually resolves them,
although just).

But anyway. I was not talking about how many colours each pixel must be
(I don't think this is important for what we are discussing, although I
might be wrong). I was rather talking about the fact that if I print at
85ppi, then it looks bad, while at (say) 300dpi it doesn't, while on a
screen, it looks perfectly ok at around 80-100ppi.
 >> Stay informed about: how come need so high dpi for printing photos?